Download Anaerobic Glucose and Serine Metabolism in Staphy

143
Journal of General Microbiology (1980), 118, 143-1 57. Printed in Great Britain
Anaerobic Glucose and Serine Metabolism in
Staphy Iococcus epidermidis
By R A M I A H S I V A K A N E S A N T A N D E D W I N A. D A W E S *
Department of Biochemistry, University of Hull, Hull HU6 7RX
(Received 30 November 1979)
Anaerobically grown Staphylococcus epidermidis fermented glucose with the production of
lactate and trace amounts of acetate, formate and CO,. Isotopic and inhibitor studies,
assays for key enzymes of different metabolic pathways, and fermentation balances, all
indicated that glucose was metabolized principally via glycolysis and to a very limited
extent by the hexose monophosphate oxidative pathway. Serine fermentation proceeded via
deamination and dismutation yielding NH, and equimolar amounts of lactate, acetate and
CO,; small amounts of formate arose by the operation of pyruvate-formate lyase. Incorporation of 0.5% (w/v) glucose in the growth medium depressed serine metabolism by
repressing the activities of serine dehydratase and pyruvate dehydrogenase but, conversely,
enhanced the activities of phosphofructokinase and lactate dehydrogenase. Glucose-grown
organisms at various stages of anaerobic batch growth showed an inverse relationship
between the rates of fermentation of serine and glucose. L-Lactate dehydrogenase activity
in crude extracts depended on fructose 1,6-bisphosphate, and fructose 1,6-bisphosphate
aldolase was found to be a class I aldolase. Despite the presence of ribokinase, D-ribose-5phosphate isomerase, transaldolase and transketolase, the organisms utilized ribose only
after growth aerobically in basal medium, and then at a slow rate after an initial lag period.
INTRODUCTION
In the course of our studies on starvation and survival of the obligate anaerobe PeptococcLis
pre'votii, we isolated Staphylococcus epidermidis from a contaminated culture. The apparent
biochemical similarities of the two organisms under anaerobic conditions, emphasizing
Willis's (1977) description of Peptococcus as the anaerobic equivalent of Staphylococcus,
led us to extend our studies to S. epiderrnidis. Since P.pre'votii utilizes serine and threonine
as its principal energy sources via dehydratase, thioclastic, phosphotransacetylase and acyl
kinase enzymes (Bentley & Dawes, 1974) but, unlike staphylococci, does not ferment
glucose to a significant extent, it became imperative to secure precise knowledge of the
anaerobic metabolism of serine and glucose in S. epidermidis, especially since information in
the literature is sparse. We have already studied aspects of the transport of serine (Horan
et al., 1978a) and of starvation and survival (Horan et al., 1978b) of S. epidermiclis and the
present work was undertaken to delineate its anaerobic serine and glucose metabolism.
Current knowledge of glucose metabolism in the facultatively anaerobic genus Staphylococcus is mainly confined to oxidative aspects (reviewed by Blumenthal, 1972). The oxidation of glucose by Staphylococcus aureus has been exhaustively studied under conditions
such as niacin and/or thiamin supplementation (Montiel & Blumenthal, 1965; Idriss &
Blumenthal, 1967), iron-rich and iron-poor states (Theodore & Schade, 1969, sub-lethal
heat (Bluhm & Ordal, 1969), pyrithiamine adaptation (Das & Chatterjee, 1962), presence or
absence of glucose (Strasters & Winkler, 1963; Montiel & Blumenthal, 1965) and presence of
f Present address: Department of Biochemistry, Faculty of Medicine, University of Sri Lanka, Sri Lanka.
0022-1287/S0/00OC-8894 $02.00 @ 1980 SGM
h f I c 118
I0
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144
R. S I V A K A N E S A N A N D E. A. D A W E S
antibiotics (Hancock, 1960). The foregoing studies showed the simultaneous operation of
Embden-Meyerhof-Parnas (EM P; glycolytic) and hexose monophosphate oxidative (HMP)
pathways as principal routes of glucose metabolism. Pan & Blumenthal (1962) tested three
coagulase-negative strains of Stnpliylococcus and observed that 93 yo of the glucose was
metabolized via the EMP pathway. Washed suspensions of S. epidermidis, grown aerobically
in vitamin-free Casitone medium without glucose, oxidized 6 to 40:/0 of added glucose via
the HMP pathway; supplementing the medium with thiamin and niacin increased oxidation by 40 to 6776 (Blumenthal. 1972). The end-products of glucose catabolism by
S. nureus vary according to the growth and experimental conditions. Lactate (73 to 94 yo)was
the major end-product of anaerobic glucose metabolism by aerobically grown S. nureus,
together with acetate (4 to 7 yo)and trace amounts of pyruvate (Theodore & Schade, 1965)
and similar results were obtained by Gardner & Lascelles (1962). The presence of the pyruvate dismutation system in staphylococci was first described by Krebs (1937).
METHODS
Organism. Staphylococcus epidermidis was isolated in our laboratory from a contaminated culture of
Peptococcrrs pre'votii. We are grateful to Dr I. Leighton (Hull Royal Infirmary) for its identification by the
biochemical tests of Schleifer & Kocur (1973) and Schleifer & Kloos (1975).
Growth of organism. Bacteria were grown in the medium and under the conditions described by Horan
et al. (1978~);where indicated glucose was excluded and this is referred to as the basal medium. Anaerobic
cultures were incubated at 37 " C ;aerobic cullures were grown at 30 "C on a gyrotary shaker at 190 cycles min-1
in conical flasks. Cysteine hydrochloride was omitted from the aerobic growth medium.
Measurement of bacterial density. The density of cultures and bacterial suspensions was measured with a
Pye Unicam SP600 spectrophotometer at 570 nm using appropriate blanks. The relationship between absorbance and dry weight was linear up to 100 /bg ml-l, corresponding to A6,0 of 0.40.
Preparation ofbacterial sicspensions. Bacteria were harvested from exponential phase cultures by centrifuging
at 12000 g for 15 min on a Sorvall RC-5 Superspeed centrifuge, washed twice with 02-free 67 mM-Na+/K-lphosphate buffer pH 6.8 (referred to as phosphate buffer) and resuspended to the required concentration in
the same buffer. Bacterial suspensions used in anaerobic experiments were held under 0,-free N,.
Bacterial extracts. These were prepared by the procedure of Bentley & Dawes (1974), homogenizing for 4
min. The broken cell suspension was centrifuged at 12000 g for 10 min at 0 "C. Extracts were usually prepared in phosphate buffer containing 10 mM-MgCI, and 100 mM-KCI unless otherwise stated. Homogenization with glass beads released 60 yo of the total cellular protein. Extracts prepared by sonicating suspensions
for a total of 6 min had very low protein contents (3 to 5 % of total protein), while passage twice through a
French pressure cell (7.58 MPa) gave extracts containing 4 to 8 "/o.
Crude cell-free extracts (5.0 ml, containing approximately 6 mg protein ml-l) were dialysed at 0 "C for
6 h against five changes each of 1 1 extraction buffer.
Manometric experiments. These were carried out at 37 "C by conventional Warburg techniques (Umbreit
et a/., 1972). Fermentation was measured as gas evolution under an atmosphere of either Nz or N,/CO,
(95 : 5 , v/v). Oxygen uptake was measured in flasks with 0.2 ml 10% (w/v) KOH in the centre well; the gas
phase was air. Vessels contained 50 pmol substrate (0.5 ml) and 2.5 ml bacterial suspension in phosphate
buffer pH 6.8; phosphate buffer was replaced by 67 m~-Tris/HClpH 7.8 in stoicheiometric experiments
because of its interference with the gas-liquid chromatographic estimation. Bacteria suspended in 37 mMNaHCO, buffer pH 7.8 and under an atmosphere of N2/COz (95 :5 , v/v) were used for the measurement of
acid production. Total COz output was measured by tipping 0.5 ml 2 M-H,SO, from a second side-arm.
Bacterial densities were 1 to 3.5 mg dry wt ml-l, except for stoicheiometric experiments and the measurement of metabolic C 0 2 from glucose, when 10 to 20 mg dry wt ml-I was used. Water replaced substrate for
controls and for measurement of endogenous metabolism.
Preparation of particidate fractions fiw N A D H and N A D P H oxidase assay. The bacterial extract was
centrifuged twice at 12000 g for 10 min at 0 "C, to remove debris and intact organisms. Microscopic examination showed no whole cells. The yellow supernatant was then centrifuged at 105000 g for 90 min at 0 "C.
The grey-brown pellet (particulate fraction) was resuspended in phosphate buffer containing 10 mM-MgCl,
and 100 ~ M - K Cwith
I a hand-held Teflon homogenizer and stored on ice.
Radioisotopic experiments. 14C02produced from [l-"C]-, [U-"C]- and [6-14C]glucoseby washed suspensions was collected in 0.05 ml 1 M-methyl benzethonium hydroxide (hyamine hydroxide) in methanol,
contained in the centre well of the Warburg vessels together with a fluted piece of Whatman no. 542 filter
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Anaerobic metabolism of S. epidermidis
145
paper. Flasks containing 30 to 40 mg dry wt cells (2.5 ml) were allowed to ferment 0.5 ml 100 mM (0.1 pCi,
3.7 kBq) labelled glucose for a period of 3 to 4 h. Buffer-bound CO, was released by tipping H,SO, and
shaking for a further 1 h. The contents of the flasks were centrifuged and the supernatant and organisms were
used for 14Cassay. The bacteria were resuspended in 10 ml phosphate buffer and 1 ml portions were filtered
through Oxoid membrane filters (0.45 pm pore size, 2.5 cm diam.), using the apparatus described by Midgley
& Dawes (1973). The bacteria were washed once with 2 ml phosphate buffer and the filters were transferred
to scintillation vials. Radioactivity in the supernatant (400 pl portions), cells and CO, was measured in a
Beckman LS-233 scintillation spectrometer, using vials containing 10 ml scintillation fluid (Bray, 1960). A
control flask with cells inactivated by boiling for 5 min was included in each set of experiments.
Analyses. Acetoin was determined by the method of Westerfeld (1945), amino acids by the ninhydrin
method (Moore & Stein, 1948) and ammonia by nesslerization. Glucose was estimated according to Hugget
& Nixon (1957) using the glucose test combination (Boehringer), lactic acid by the Barker & Summerson
(1941) method and protein by the Lowry method. Volatile fatty acids and lactic acid were determined by gasliquid chromatography. The fermentation mixture (cell-free) was first passed through a Dowex 50W-X8 ionexchange resin (100 to 200 mesh, Hf form) to remove metal cations. The fatty acids were converted to their
tetra-n-butylammonium salts and then benzylated using benzyl bromide according to the procedure of
Bethge & Lindstrom (1974). Crotonic acid was the internal standard (Jones & Kay, 1976). The esters were
separated on a column of 10 "/o (w/w) diethylene glycol succinate polyester (stationary phase) on Supelcoport
80 (support) (Chromatography Services Co., Wirral, Merseqside) at 140 "C, with an argon flow rate of 15 ml
min-l. For benzyl lactate a temperature of 190 "C was employed.
Enzyme assays. Enzymes in bacterial extracts were assayed spectrophotometrically at 25 "C with a Pye
Unicam SP1800 spectrophotometer using, as appropriate, silica or glass cuvettes of 1 cm light path. Optimum
conditions for each enzyme were ascertained except for transketolase, transaldolase and ribokinase. Unless
otherwise stated, assays were initiated by the addition of extract and substrate was omitted from control
cuvettes.
Hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, hexosephosphate
isomerase, phosphofructokinase, fructose 1,Qbisphosphate aldolase, triosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, acetate kinase, serine dehydratase, ribokinase,
transaldolase, transketolase, NADH oxidase, NADPH oxidase and NADPH-NAD transhydrogenase weIe
all assayed in direct or coupled assays by measuring
min-l due to oxidation or reduction of the appropriate nicotinamide nucleotide. Specificactivities are expressed as pmol product formed min-l (mg protein)-l.
The total volume of the assay mixture was 1 ml. The specific activity of NAD-independent lactate dehydrogenase is expressed as pmol 2,6-dichlorophenolindophenol(DCPIP) reduced min-l (mg protein) -l and the
value of 19.85 1 mmol-1 cm-l was taken as the millimolar absorption coefficient for DCPIP at pH 6.8.
Specific activity of ~-ribose-5-phosphateisomerase is expressed as units min-l (mg protein)-' (one unit is
= 1.0). For the pyruvate-formate lyase (exchange enzyme), one unit of activity is defined as the amount
of enzyme which incorporates from [14C]formate(0.1pCi ml-l, 3.7 kBq ml-l) 1 d.p.m.(pmol pyruvatej-l min-l
under standardized reaction and counting conditions ; specific activity is expressed as units (mg protein)-'.
The crude extract for the pyruvate-formate exchange assay was prepared in phosphate buffer containing
3 m~-2,3-dimercaptopropanol and 1 mM-FeSO, and the concentration of these two reducing agents in the
final assay mixture was adjusted to the same value by appropriate additions because this enzyme is extremely sensitive to oxygen and maintenance of a low redox potential is necessary to preserve exchange
activity (Lindmark et al., 1969). Table 1 records the assays employed and any modifications to the published
procedures are noted.
Calculation of A TP yieZds from fermentation products. The following assumptions, based on the enzymic
evidence obtained, were made for the calculation of ATP yields from fermentation products. Lactate is
produced via glycolysis and lactate dehydrogenase with the simultaneous production of 1 net mol ATP
(mol lactate)-l, and acetate with 2 net mol ATP (mol acetate)-l, one produced during the formation of
pyruvate by glycolysis and one during the conversion of pyruvate to acetate (via phosphate acetyltransferase
and acetate kinase). These assumptions accord with those of Dirar & Collins (1972).
Chemicals. Analytical grade chemicals were used whenever possible. Enzymes and coenzymes were obtained from Sigma, Boehringer and PL-Biochemicals. Radiochemicals were purchased from The Radiochemical Centre, Amersham.
10-2
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Amelunxen &
Carr (1975)
NAD-linked lactate
dehydrogenase
(EC 1.1.1.28)
NADP-linked lactate
dehydrogenase
NAD-independent
lactate dehyd rogenase
(EC 1.1.2.4)
Phosphate
acetyltransferase
(EC 2.3.1.8)
Snoswell (1959)
Acetyl phosphate, 5; coenzyme A, 0.42
Buffer, pH 8.0, 50; DL-glyceraldehyde
3-phosphateY0.15. Initiated with NAD
Krietsch (1975)
Bentley & Dawes
(1974)
Buffer, pH 7.7, 90
Lebherz & Rutter
(1973)
Buffer, pH 6.8; NADH, 0.3; fructose
l,Qbisphosphate, up to 10;
sodium pyruvate, 7-5
Phosphate buffer, pH 5.8, 100; NADPH,
0.3; sodium pyruvate, 7.5
Buffer, pH 6.8
NADH, 0.3
Brock (1969)
Schleifer & Kocur
(1973)
Buffer, pH 7.5; fructose 6-phosphate, 2.5
Gracy & Tilley
(1975)
Hexosephosphate
isomerase
(EC5.3.1.9)
6-Phosphofructokinase
(EC 2.7.1.11)
Fructose-lY6-bisphosphate
aldolase
(EC 4.1.2.13)
Triosephosphate
isomerase
(EC 5.3.1.1)
Gl yceraldehyde-3-phosphate
dehydrogenase
Tris/HCl buffer, pH 8.2, 5.0
Pontremoli &
Grazi (1966)
Buffer, pH 8.0, 100; NADP, 0.4;
6-phosphogluconate, 2-5
Buffer, 100; glucose 6-phosphate, 1.5;
NADP, 0.4; MgS04, 15
Buffer, pH 8.1, 100; MgCl,, 10; ATP, 2.5;
glucose, 50. Initiated with ATP
6-Phosphogluconate
dehydrogenase
(EC 1.1.1.44)
Kuby & Noltmann
(1 966)
Glucose-6-phosphate
dehydrogenase
(EC 1.1.1.49)
Reference
McGill & Dawes
(1971)
Hexokinase
(EC2.7.1.1)
Enzyme assayed
Modifications to the assay
(concentrations in m)
3.0
6-8
100-200
2.3
5-8
50-100
1.2
0.04
1.8
5.8-6.9
(6.8)
8.0
7.7
0.03
0.3
0.3
0.3
0.04
1.6
2-6
100-200
15-30
50-150 7-2-8.1
(7.6)
7.5
8.2
25-60
50-150
8-0
8-0
8.1
50-100
250-500
250-500
-
0.2
0.01
WAD)
No activity
(NADP)
0-07
-
-
0-3
-
0.03
(NADP)
No activity
"AD)
0.02
(NADP)
No activity
WAD)
0.7
Protein Opti- Apparent K,,, (mM)
per assay mum
(pg)
pH* Substrate Cofactor
Extracts were prepared in 67 mM-Na+/K+ phosphate buffer containing 10 mM-MgCI, and 100 mM-KCI, unless otherwise indicated.
Table I. Enzymes of carbohydrate and serilze metabolism in S. epidermidis grown anaerobically in glucose medium
0.08
14.4
8-8 (a)
8-6 (b)
0.24
0.24
0.11
0.10 (a)
0.04 (b)
0.3
0.22 (a)
0.23 (b)
2.4
2.1
0.21
0-24 (a)
0.19 (b)
0.07
0.07 (a)
0.04 (b)
0-024
0.016 (a)
0.013 (b)
Specific
activity?
bmol
min-l (mg
protein)-l]
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-
-
100-200
150-250
100-250
None
None
None. Method was checked with extracts of
Pseuclomonas aeriiginosa
-
-
100-200
None
0.06
0.03
0.03
2.0
0.02
0.02
-
-
-
-
-
-
-
-
3.3
ND
ND
ND
ND
ND
0-02
0.1 1
0.375
3.2#
2.2
2.1 (a)
2.1 (0)
0.1 5
5.7
-
0.25
1.4
t
A range indicates a plateau of maximum activity; the assay pH is given in parentheses. NT, Not tested.
(a) Extracts were prepared in phosphate buffer containing 10 mM-MgC1,; (b) extracts were prepared in phosphate buffer. ND,Activity not detected.
$ Units (mg protein)-l.
5 Units min-l (mg protein)-l.
*
Gonzalez-Cerezo
& Dalziel
(1975)
Senior & Dawes
(1971)
-
150-250
None
NT
150-250
300-500 7.5-8.1
(7.8)
150-250 NT
None
None
Strecker (1955)
Domagk & Doering
(1975)
de Vries et al.
(1967)
de Vries et al.
(1967)
de Vries et al.
(1967)
McGill & Dawes
(1971)
Dawes et al.
(1966)
Dawes et al.
(1966)
Dawes et al.
(1966)
Wood (1971)
NADH oxidase
(EC 1.6.99.3)
NADPH oxidase
(EC 1.6.99.1)
Ribokinase
(EC 2.7.1.15)
Pyruvate-formate lyase
(exchange enzyme)
~-Ribose-5-phosphateisomerase
(EC 5.3.1.6)
Transketolase
(EC2.2.1.1)
Transaldolase
(EC 2.2.1.2)
Phosphoketolase
(EC4.1.2.9)
Ethanol dehydrogenase
(EC 1.1.1.71)
NADPH-NAD
transhydrogenase
(EC 1.6.1.1)
Glycerol-3-phosphate
dehydrogenase
(EC 1.1.1.8)
6-Phosphogluconate
hydro-lyase + 3-deoxy2-0x0-6-phosphogluconate
aldolase
NT
Sodium formate, 0.25 pCi nil-l. CO,
absorbed in hyamine hydroxide
Buffer, pH 7.8. Incubation for 2.5 or 5 min
Reed & Willms
(1 966)
Pyruvate dehydrogenase
complex (EC 1 .2.4.1)
2200
Glycylglycine buffer, pH 8.3, 100; acetyl
3-15
8.3
phosphate, 10; ADP, 2.5; MgCI,, 5
Glycylglycine buffer, pH 7.5, 100; serine, 25; 10-25 7.2-7.8
NADH, 0.1 5 ; lactate dehydrogenase, 10
(7.5)
units
Buffer, pH 7.2. Incubation for 5 min with
300-600
7.2
extracts of glucose-grown organisms and
2 niin with basal medium-grown organisms
Phosphate buffer, pH 7.2, 100; NADH, 0.15 100-250 6.9-7-5
(7.2)
250-500
6.0
Phosphate buffer, pH 6.0, 100; NADPH,
0.15
None
100-200
NT
Pelroy & Whiteley
(1971)
Eentley & Dawes
(1974)
Acetate kinase
(EC 2.7.2.1)
L-Serine dehydratase
(EC 4.2.1.13)
Table 1 (cont.)
148
R. S I V A K A N E S A N A N D E. A. D A W E S
Table 2. Effect of composition of growth medium on fermentative activitj'
of washed suspcnsions of S. epidermidis
Bacteria were harvested from the exponential phase of anaerobic growth and initial rates of fernientation were determined. Metabolic CO, formation was measured in phosphate buffer under N2; acid
production was measured as COBdisplaced frani bicarbonate under an atmosphere of N,/CO,
(95 :5 , v/v). Results are expressed as the mean k standard deviation and values in parentheses indicate the number of determinations. The substrate values have been corrected for the endogenous
rates; acid production values have not been corrected for metabolic CO,.
--
Rate of fermentation [nmol CO, h-' (mg dry wt)-']
-
Bacteria grown in basal medium
Substrate
CO, formation
Acid production
Glucose
Serine
Pyruvate
Endogenous
3 4 k 6 (6)
174005 2500 (8)
25005- 500 ( 5 )
11 k 4 (6)
900 k 200 (8)
____
__
~
Bacteria grown in basal medium
+ 0.5 0 o (w/v) glucose
- ~-~
-
~
c - -~
CO, formation
114k 14 (6)
3700 k 800 ( I 3)
2600k 140 ( 5 )
12+5 (6)
-
__
30 5 30 (9)
~
Acid production
1700+450 (12)
__
-
130130 (13)
Ribose, niannitol and lactose were not fermented.
Table 3. Stoicheiometrlv offermentation of glucose, fructose and serine
S. epidermidis
bji
Bacteria were grown anaerobically in basal medium containing 0.5 (w/v) glucose and harvested
during late-exponential phase. Fermentation was carried out for 3 h in Warburg vessels containing
50 mg dry wt bacteria. Formate, acetate and lactate were estimated by gas-liquid chromatography
and ammonia by nesslerization of centrifuged flask contents to which H2SO4had not been added at
the end of the reaction. The recorded values for glucose, fructose and serine fermentations have
been corrected for the products formed endogenously.
Substrate
Endogenous
Glucose
Fructose
Endogenous
Serine
Endogenous
Serine
Amount of
substrate
(pmol)
-
48-8
50.0
__
100.0
50.0
Products (pm01)
_
_
CO,
1.9
3.0
2.1
1.0
44.1
0.9
22-8
_
.
_
~
_
_
_
Formate
2.0
3.7
4.8
1.8
10.8
1-7
6.1
_
_
_
Acetate
5.8
4.8
4.6
5.0
51.9
4.2
23-8
~
-
A
~
-
Lactate
8.9
87.6
88.5
9.1
46.0
7.8
23.7
-
-
~
-
-
Ammonia
3.5
0
0
3.6
97.8
3.9
48.9
~
Recovery
ofcarbon
(O0)
__
96.3
95.4
-
98.9
98.4
RESULTS
Growth yields. The basal medium supported the growth of 146 & 1 1 (standard deviation for
8 determinations) p g dry bacterial wt ml-l. With an added energy source the growth yield
was a linear function of glucose concentration up to 30 mM, and of serine up to 50 mM
(coefficients of correlation 0.95 and 0.99, respectively). The molar growth yields were ( g
mol-l): Yg,,,co8a
= 21-4 and Ykerine
= 6.7.
Fermentation of various substrates by washed suspensions. Glucose and serine were fermented rapidly by anaerobically grown organisms but ribose, mannitol and lactose were not
utilized (Table 2). However, analysis of supernatants revealed that ribose disappeared at an
initial rate of 42 nmol h-l (mg dry wt)-l and subsequent transport measurements confirmed
the uptake of ribose by the organism (N. J. Horan, R. Sivakanesan & E. A. Dawes, unpublished observations). The incorporation of glucose in the basal medium stimulated
glucose fermentation by 85 7;)and depressed that of serine by 79 yo in the well known 'glucose effect '. Unexpectedly, the fermentation of pyruvate was not influenced, but extracts
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149
Anaerobic metabolism of S. epidermidis
.L
0-0
/
.-.-.
0
20
0-0
60
Time (min)
40
1
80
100
Fig. 1 . Anaerobic fermentation of glucose by washed suspensions of S. epidermidis. Bacteria were
harvested after 10 h anaerobic growth (425 p g dry wt ml-l) in basal medium supplemented with
0.5 7; (w/v> glucose. Glucose (0)
and lactate ( 0 )were determined in samples withdrawn from a
suspension (14 mg dry wt ml-l) held under N, and containing 16.6 mM glucose. C 0 2 output (D)
was corrected for endogenous metabolism.
from bacteria grown in basal medium metabolized pyruvate at some 2-5 times the rate of
extracts from bacteria grown in glucose-containing medium (Table 5). Therefore, entry of
pyruvate into cells could be the critical factor, as suggested for S. aureus by Das & Chatterjee
(1 962).
Products of glucose, fructose and serine fermentation. The products of glucose and fructose
fermentation were similar, with lactate as the major product and CO,, acetate and formatelas
minor products (Table 3). The overall stoicheiometry was
+
1 Glucose -+ 1-80 Lactate +0.10 Acetate +0.075 Formate 0.06 C 0 2
corresponding to an ATP yield of 2.0 mol (mol glucose)-l. The course of glucose fermentation is shown in Fig. 1 ; CO, was the sole gaseous product and acetoin was not detected.
Recovery of carbon from added glucose was 96% and experiments with [U-14C]glucose
(Table 6) showed that 3% of the radioactivity was associated with the cells. Fermentation of
serine (Table 3) corresponded to a stoicheiometry of
1 Serine -+ 0.46 Lactate + 0.52 Acetate +0.1 1 Formate + 0.44 CO, +0.98 NH,
indicating that pyruvate was predominantly dismutated according to the equation
+
+
2 Pyruvate -+ Lactate Acetate CO,
The ATP yield is 0.52 mol (mol serine)-l.
Eflect of growth phase on fermentative capacity. The rates of fermentation of glucose and
serine were compared as a function of the growth cycle in basal and glucose-supplemented
media (Figs 2a, b). In both media the endogenous metabolic rate was highest in the early
stages of growth, but remained fairly low throughout. Bacteria harvested from the basal
medium showed a similar pattern for serine and glucose metabolism (Fig. 2a) with maximum
activity in mid-exponential phase. However, in glucose-containing medium, organisms at
various stages of growth exhibited greatest activity towards serine when glucose metabolism
was minimal and the decline in serine metabolism reflected a rise in glucose metabolism
(Fig. 2b). Sevag & Swart (1947) showed an inverse relationship between the ability to
metabolize glucose and pyruvate in S. aureus and also suggested that organisms derived from
glucose-free medium dismutated pyruvate, while those from glucose-containing medium
principally oxidized pyruvate, i.e. different patterns of metabolism were operating under
these conditions.
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150
R. S I V A K A N E S A N A N D E A. D A W E S
5
Time (11)
10
14
800
-$
700
n
600
2 500
M
5
.-.I
$ 400
100
0
5
Time (h)
10
15
Fig. 2. Effect of phase of growth on fermentative capacity. Bacteria were grown anaerobically in (a)
basal medium and (0) basal medium + 0.5 7; (w/v) glucose. Basal medium was inoculated with an
anaerobic 7.5 h culture (105 pg dry wt ml-I) and glucose-supplementedmedium with a 9.5 h culture
(375 pg dry wt ml-l). Fermentation rates were nieasurcd manometrically as CO, release (see Methods
and Table 2). 0,
Growth; e, endogenous metabolism (COzvia acid production); U, CO, via acid
production from glucose; a, COLformation from serine. Note the different scales in ( a ) and (0).
Products of endogerzous metabolism. The principal products of anaerobic endogenous
metabolism were lactate, acetate, formate, C 0 2 and NH3 (Table 3). The ammonia was
derived from both RNA and the amino acid pool; both were depleted markedly during the
initial 3 h starvation while the cellular protein content remained essentially constant (Horan
et al., 1978b).
Oxidation of various substrates by aerobically grown washed suspensions. Of the substrates tested only niannitol and lactose were not oxidized (Table 4). However, supplementation of the basal medium with glucose caused varying degrees of suppression of
oxidation rates with all substrates except glucose and fructose. Gluconate and ribose were
oxidized only by organisms grown in basal medium and then only at a low rate and after a
lag period. Cells harvested from 0-5v/0(w/v) ribose medium oxidized ribose at the rate of
2.9 pmol h-l (mg dry wt)-l without any lag.
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151
Anaerobic metabolism of S. epidermidis
Table 4. Rates of oxidation of various substrates by washed suspensions of
aerobically grown S. epidermidis
Oxidation was measured manometrically at 37 "C with organisms harvested from the exponential
phase of growth. Rates were calculated from the initial linear uptake which persisted for 30 min in
most cases. Wherea lag occurred the subsequent linear rate was recorded. Substrate values have been
corrected for the endogenous rate and results are expressed as the mean L standard deviation, with
the number of determinations in parentheses.
Rate of oxidation [pmol 0, h-I (mg dry wt)-']
A
7
-
Substrate
Glucose
Fructose
Ribose
Gluconate
Pyruvate
Lactate
Serine
Endogenous
Bacteria grown in
basal medium
4.6 0.3 (7)
4.0-t 0.7 (6)
0.4-tO-2 (3)*
0-14kO.03 (2)*
7.1 k 0 . 3 (2)
9.3 k 1.0 (4)
8.720.9 (7)
0.8 0.2 (8)
Bacteria grown in
basal medium
+0.5 16 (w/v) glucose
7
6.7 0.4 (5)
6.1 & 0.2 (2)
0
0
6*6+0*1(3)
7.5 -t 0.3 (3)
3*0_+1.2 (4)
0-850.3 (8)
Mannitol and lactose were not oxidized.
* After an initial lag which did not exceed 30 min.
Enzymes of glucose and serine metabolism. The specific activities, optimum p H and apparent K,, values for substrates and cofactors of various enzymes of glucose and serine
nietabolism in extracts were studied (Table 1). Many of these enzymes displayed increased
activity when extracts were prepared in the presence of 10mM-MgC1, and 100mM-KCI
(Table 1). The operation of glycolysis suggested by the fermentation balance is supported by
the presence of the key enzymes phosphofructokinase, fructose-l,6-bisphosphatealdolase
and triosephosphate isomerase ; a highly active NAD-dependent lactate dehydrogenase was
also present.
The operation of the oxidative pentose phosphate pathway for the production of pentoses
is indicated by the presence of NADP-specific glucose-6-phosphate dehydrogenase and 6phosphogluconate dehydrogenase ; transketolase, transaldolase and ribose-5-phosphate isornerase were also present. In the absence of NADPH-NAD transhydrogenase, the NADPlinked lactate dehydrogenase will regenerate the NADP needed for the initial steps of this
pathway.
Serine dehydratase, the pyruvate dehydrogenase complex, phosphate acetyltransferase and
acetate kinase were also present in crude extracts of organisms grown anaerobically. Thus
the pathway for serine metabolism in S. epidt.rmidis differs from that in P.pre'votii (Bentley &
Dawes, 1974) in not significantly employing the thioclastic reaction for the further metabolism of pyruvate; hydrogen is not produced and only a small amount of formate appears.
Serine dehydratase was specific for L-serine and in crude extracts lost activity at the rate
of 8.30/, h-l when held at 0 "C in phosphate buffer, and completely at room temperature
over a period of 7 h. Various additions to the buffer did not significantly alter this rate, e.g.
I mmdithiothreitol, 6.5 yo h-l; 10 mM-thioethanol, 7.6 yo h-l; 10 mM-MgC1, plus 100 mMKCI, 7.0% h-l.
The activity of NAD-linked lactate dehydrogenase in extracts was influenced by fructose
1,6-bisphosphate. When extracts were incubated with the reaction mixture for 1 h, the
enzyme lost activity gradually, whereas the presence of fructose 1,6-bisphosphate (10 mM)
arrested such a decline (Fig. 3). Dialysis of bacterial extracts (prepared in phosphate buffer
containing 10 mM-MgC1, and 100 mM-KCl and dialysed against the same buffer, as des-
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152
R. S I V A K A N E S A N A N D E. A. D A W E S
zz
2
E,
Y
4
t
10
20
30
40
50
Period of pre-incubation (min)
60
Fig. 3. Effect on the activity of lactate dehydrogenase of pre-incubation of bacterial extract with the
reaction medium in the absence (0)
or presence ( 0 )of 10 mwfructose 1,6-bisphosphate. Samples
(0.98 ml) were withdrawn from reaction medium (19.6 ml) held at 25 "C, and reaction was initiated
by the addition of 20 pl 15 mwNADH. The composition of the reaction medium and assay procedures were as described in Methods. Extracts were prepared from bacteria grown anaerobically in
glucose-supplemented medium.
cribed in Methods) resulted in nearly 50 % loss of the lactate dehydrogenase activity. However, when the dialysed extract was incubated with fructose 1,6-bisphosphate (10 mM) in the
reaction mixture for 5 min prior to initiation of the reaction with NADH, 87% of the
lactate dehydrogenase activity lost on dialysis was restored. With undialysed extracts, if the
reaction was initiated with NADH in the absence of fructose 1,6-bisphosphate, the activity
of lactate dehydrogenase was only 66 % of that obtained when reaction was initiated by the
addition of the extract; the presence of 4 mmfructose 1,6-bisphosphate was necessary for
maximum lactate dehydrogenase activity when the reaction was initiated with NADH.
Supplementation of the reaction mixture with fructose 1,6-bisphosphate did not affect the
activity when the reaction was initiated with bacterial extract. The decline in lactate dehydrogenase activity thus observed under different experimental conditions suggests that
either stabilizing amounts of fructose 1,6-bisphosphate are rapidly removed from incubated extracts, presumably by metabolism, or the enzyme is reversibly inactivated when
incubated in the absence of fructose 1,6-bisphosphate. While this work was in progress, the
presence of a fructose 1,6-bisphosphate-activatedlactate dehydrogenase in S. epidermidis
was reported by Gotz & Schleifer (1978) who showed that fructose 1,6-bisphosphate is
necessary to stabilize the tetrameric form of the enzyme.
Fructose-l,6-bisphosphatealdolase in extracts had a broad pH optimum and was insensitive to 10 mM-EDTA. The activity of extracts prepared and dialysed in phosphate buffer
was enhanced slightly by 10 m~-MgCl,(6%) and 100 mM-KCl (8 yo).Partially purified
aldolase (75-fold) was completely active in the presence of 20 mM-EDTA, showed a broad
pH optimum towards fructose 1,6-bisphosphate, and cleaved fructose 1-phosphate at a much
slower rate (fructose 1,6-bisphosphate to fructose 1-phosphate activity ratio = 55). Its
activity was not stimulated by the presence of K+, Mg2+ or Zn2+. In common with class
I aldolases, the enzyme was inactivated by incubation with dihydroxyacetone phosphate in
the presence of NaBH, suggesting the formation of an enzyme-substrate Schiff base complex
(R. Sivakanesan & E. A. Dawes, unpublished observations). Therefore the aldolase of S .
epidermidis is a class I aldolase, the occurrence of which has been reported in several
prokaryotes, e.g. Micrococcus aerogenes (Lebherz & Rutter, 1973),staphylococci and Q-cocci
(Gotz et al., 1978). However, in contrast to other class I aldolases, the catalytic activity of the
purified enzyme was not affected by incubation with carboxypeptidase A.
Eflect of growth conditions on enzyme activities. The enzymic activities of organisms
grown under four different conditions were examined (Table 5). Anaerobic growth in the
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153
Anaerobic metabolism of S. epidermidis
Table 5. Eflect of growth conditions on the activities of enzymes of carbohydrate
and serine metabolism in extracts of S. epidermidis
Activities are expressed as the mean
+ standard deviation, with the number of determinations
in parentheses.
Specific activity [pmol min- (mg protein)-l]
7p--p---ph
Anaerobic growth
A
-----
Enzyme
Serine dehydratase
Hexokinase
Phosphofructokinase
Fructose- 1,6-bisphosphate
aldolase
Lactate dehydrogenase
(NAD-linked)
Glucose-6-phosphate
dehydrogenase
6-Phosphogluconate
deh ydrogenase
Transketolase
Transaldolase
Pyruvate dehydrogenase
Ribokinase
Basal medium
+0.5 ''6 (w/v)
glucose
2.2k0.2 (8)
0.07 -t 0.01 (8)
0.11 kO.01 (6)
0.30 0.03 (8)
14.4f 1.6 (6)
____ 7
Aerobic growth
77
-
7
Basal medium
Basal medium
+0*5"'0 (w/v)
glucose
Basal medium
6.0 -t 0.9 (8)
0.06 h 0.03 (8)
0.036 & 0.003 (6)
0.29 k 0.05 (6)
2.0-t 0-3 (6)
0.15 f0-02 (8)
0.08 f0.01 (8)
0.22 & 0.05 (8)
5.4 & 0.7 (6)
0.14f 0.02 ( 5 )
0.033 f0.005 (8)
0.24 & 0.04 (6)
6.6k0.8 (3)
7*4+1.0 (6)
2.9 & 0.4 (4)
+
0.024f 0.003 (8) 0.023 0.015 (6) 0*04+0.01(8)
0.025 f0-004 (6)
0-21k 0.02 (8)
0-25+0*2 (8)
0.17+0.02 (8)
0 ~ 1 0 + 0 ~ 0(4)
1
0.01 8 f0-004 (4)
0.18 f0.02 (2)
0~012f0~002
(3)
0.1 1st 0.01 (4)
0.012 k 0.002 (4)
0.362 0.06 (2)
0-024f0.011 (4)
+
0.1 1 0.01 (4)
0.019 2 0.005 (4)
0.15 2 0.02 (5)
0-03+ 0.01 (4)
0.20 0.01 (6)
+
0.13 0.02 (4)
0.017 f0.001 (4)
0-38f0.04 (2)
0.014+0*005 (4)
presence of glucose enhanced the activities of phosphofructokinase and lactate dehydrogenase, but aerobically in the presence of glucose the activities of phosphofructokinase,
lactate dehydrogenase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were increased. Hexokinase activity was much higher in aerobically grown
bacteria.
Serine dehydratase and pyruvate dehydrogenase activities were repressed some 64 yo and
55 yo, respectively, by glucose, irrespective of the conditions of aerobiosis, thus accounting
for the observed fermentative and oxidative behaviour of whole organisms (Tables 2 and
4).
NADH and NADPH oxidases and NADPH-NAD transhydrogenase. The distribution of
NADH and NADPH oxidase activities in the particulate and soluble fractions of extracts
suggests that the preparative procedure solubilized appreciable amounts of the enzymes. N o
satisfactory separation of NADH and NADPH oxidase activities could be achieved by
differential centrifugation and ammonium sulphate fractionation of crude extracts, and it is
possible that both activities are associated with the same protein. NADPH-NAD transhydrogenase activity was absent from bacterial extracts.
Fermentation of [ 1J4C]-, [6J4C]- and [U-14C]glucose.The radiochemical balances for the
fermentation of uniquely labelled glucose by washed suspensions are recorded in Table 6
together with the total COz released in the Warburg apparatus. The cumulative yield of
I4CO2from [l-14C]glucose ranged from 0.9 to 1.8y0, hence the HMP pathway plays an
insignificant role in anaerobic glucose metabolism. CO, derived from either the C-1 or C-6
positions of glucose represented only about 20% and 2%, respectively, of the total CO,
released. After fermentation of [U-14C]glucose,the total radioactivity taken up by the
bacteria was 374 ;the majority of it was released by acid treatment leaving only 0-5% in the
cells.
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154
R. SIVAKANESAN A N D E. A. D A W E S
Table 6. Fermentation of labelled glucose by S. epidermidis
Bacteria were harvested from the exponential phase of anaerobic growth in medium containing
0.5 o/b (w/v) glucose and washed suspensions were prepared. Reactions were carried out in a Warburg
apparatus. Total CO, release was measured manometrically in one set of vessels and 14C02was collected in hyamine hydroxide in the centre wells of another set, as described in Methods. Total CO,
output was corrected for endogenous controls. The specific radioactivities of glucose used were
[c.p.m. (pniol C)-l]: l-14C, 1841; 6-11C,2193; UJ4C, 287. Controls showed no 14Cin either the cells
or CO,.
C 0 2 from
glucose (pmol)
l"o,
(0,; total
Substrate
Radioactivity-1(c.p.m.)
---*-7
co,
L
7
Calc. from
released)
Supernatant radioactivity Warburg
pmol
Expt* CO,
Label
--
1J4C
2.25
19.1
0.85
4-07
20.9
82801
(98.3)
80841
(96.0)
3.25
2.0
162.5
71509
(98.2)
69677
(95.8)
3.37
3.23
104.3
108953
0.08
182
4.93
(99.3)
(0.2)
266
124298
0.12
B
(97.7)
(0.21
193
111442
0.09
4.56
50
A
(99.2)
(0.2)
* Experiments were with (A) and without (B) acid being tipped.
t Values in parentheses are percentages of the total radioactivity.
1.6
50
A
B
1JV
50
A
U-lT
50
A
B
U-1AC
46.7
A
B
6-l'C
6-l'C
50
800
(0.9 1
764
(0.9)
1570
(1.8)
87337
(98.5)
82408
(97.5)
87294
(97.3)
934
(1.1)
867
(1.0)
966
(1.3)
880
(1.2)
0-43
0.42
3.02
3.07
A
2.0
DISCUSSION
Fermentation balances (Table 3), enzymic analyses (Table 1) and experiments with
specifically labelled glucose (Table 6) indicate that anaerobically S. epidernzidis metabolizes
glucose principally via glycolysis with lactate as the major product; the small amounts of
acetate and formate produced can be accounted for by the minor operation of a pyruvateformate lyase and CO, production results from the HMP pathway and pyruvate dehydrogenase activity. Pyruvate dismutation will also yield equimolar amounts of acetate and
lactate. A very minor involvement of the HMP pathway is supported by the release of
WO, from [l-14C]glucose, the presence of the relevant enzymes and an NADP-linked lactate dehydrogenase which, in the absence of NADPH-NAD transhydrogenase, would permit
re-oxidation of NADPH. Arsenite inhibition of pyruvate dehydrogenase approximately
halved the yield of CO, from 50 pmol glucose (from 3.2 to 1.5 mol) (R. Sivakanesan &
E. A. Dawes, unpublished results). Strasters & Winkler (1963) reported that aerobically
grown S. aureux quantitatively fermented glucose to lactate in the presence of arsenite and
Strasters (1962) did not consider the HMP oxidative pathway to be active for glucose
catabolisin in this organism under anaerobic conditions. The proportion of glucose utilized
via the HMP pathway in S. aureus apparently depends on various factors Thus aerobic
growth (Strasters & Winkler, 1963), growth in the absence of glucose (MontieI & Blumenthal,
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Anaerobic metabolism of S. epidermidis
155
1965; Strasters & Winkler, 1963), growth in the presence of high concentrations of nicotinic
acid (Montiel & Blumenthal, 1965; Idriss & Blumenthal, 1967) and incubation of washed
suspensions with niacin(Hoo et al., 1971) all increased the participation of theHMP pathway.
About 90% of the pyruvate formed after initial deamination of serine underwent dismutation to lactate, acetyl-CoA and COz and the rest was metabolized by the pyruvateformate lyase system producing acetyl-CoA and formate. Acetyl-CoA yielded ATP via
the operation of phosphate acetyltransferase and acetate kinase. This contrasts with P. pre'votii
in which acetate, COz and H2 are produced in equimolar amounts from pyruvate (Bentley &
Dawes, 1974).
The absence of the Entner-Doudoroff pathway conforms to the general pattern observed
with Gram-positive cocci such as S. aureus (Strasters & Winkler, 1963), Sarcina lutea
(Dawes & Holms 1958a, b), Micrococcus and Myococcus (Kersters & De Ley, 1968); the
exceptions are some Nocardia strains (Kersters & De Ley, 1968) and gluconate-grown
Streptococcus faecalis (Sokatch & Gunsalus, 1957). Phosphoketolase activity was not detected in extracts from anaerobically grown S. epidermidis and Strasters & Winkler (1963)
also found no evidence for this pathway in S. aureus, even when it was grown in gluconate
medium.
Anaerobically grown S. epidermidis failed to ferment ribose, and during anaerobic starvation
the ribose produced in RNA breakdown was not utilized (Horan et al., 1978b). The inability of s. aureus to ferment ribose, and also to oxidize it after aerobic growth in the
presence of glucose, has been explained by the absence of ribokinase (Strasters & Winkler,
1963). However, we detected ribokinase activity in bacteria grown under four different
conditions (Table 5), and therefore the regulation of ribose metabolism seems to be controlled by a more intricate mechanism. Recently, genes implicated in penicillinase synthesis
have been located on a plasmid which also controls aerobic fermentation of mannitol and
ribose in S. epidermidis (Nazar et al., 1977).
The presence of glucose in the growth medium had a marked influence on the fermentation
and oxidation of substrates, other than pyruvate, by whole organisms; pyruvate entry into
cells wa probably the rate-limiting step. Stimulation of aldolase, lactate dehydrogenase,
aconitase, isocitrate dehydrogenase, glucose-6-phosphatase and glutamate-oxaloacetate
aminotransferase activities in a coagulase-negative Staphylococcus was observed when the
glucose concentration of the medium was increased to 0-5y0, and with 1 o/o glucose, suppression of lactate dehydrogenase, aconitase and isocitrate dehydrogenase activities occurred
(Ivler, 1965). Under our experimental conditions, with medium glucose concentrations of
0.5 yo (w/v), the activities of serine dehydratase and the pyruvate dehydrogenase complex
were repressed by 64 yo and 55 %, respectively, irrespective of the conditions of aerobiosis,
thus explaining the difference between the glucose-grown organisms and those grown in
basal medium in their capacity to metabolize serine. Conversely, the presence of glucose in
the growth medium enhanced the activities of phosphofructokinase and lactate dehydrogenase in keeping with the increased capacity of the glucose-grown organisms to utilize
glucose.
We thank the University of Hull for the award of a Research Studentship. The work was
carried out while R. Sivakanesan was on leave of absence from the University of Sri Lanka.
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