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Chapter 22
High G + C
Gram-Positive Bacteria:
The Actinobacteria
1
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High G + C Bacteria
• volume 4 of Bergey’s Manual of
Systematic Bacteriology, 2nd Edition
• Actinomycetes
– gram-positive, aerobic bacteria that
produce filamentous cells called hyphae and
differentiate into asexual spores
– adapt to climates similar to fungi
2
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Figure 22.1; phylogenetic relationships
among Bacteria and Archaea
3
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General Properties of the
Actinomycetes
• source of most currently used antibiotics
• also produce metabolites that are anticancer,
antihelminthic, and immunosuppressive
• They have complex life cycle
• most are not motile
– motility is restricted to flagellated spores
4
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Life Cycle of Actinomycetes
• involves development of filamentous cells
(hyphae) and spores
• hyphae can form branching network
– can grow on surface of substrate or into it to
produce a substrate mycelium
– some hyphae differentiate to form an aerial
mycelium which extends above substratum
– at this stage Actinomycetes, forms secondary
metabolites, some of which are medically useful
5
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Figure 22.2; cross section of an
actinomycetes colony
6
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Life Cycle of Actinomycetes…
• aerial mycelium
– form exospores which are called
sporangiospores if they are located in a
sporangium
• produced in response to nutrient deprivation
• withstand desiccation but not heat resistant
• spores dispersed by wind form new bacteria
7
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Figure 22.3; examples of
Actinomycetes spores as seen by SEM
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Ecological Significance of
Actinomycetes
• widely distributed in soil
• play important role in mineralization of
organic matter
• most are free living, but a few are
pathogens
9
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Characteristics Used in Actinomycete Taxonomy
• four major cell wall types based on
peptidoglycan structure and sugar content
other than N-acetylglucosamine and Nacetylmuramic acid
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Figure 22.4; Actinobacterial peptidoglycan
structure
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12
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Figure 22.5; classification of the phylum
Actinobacteria
13
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Phylum Actinobacteria
• 16S rRNA evidence shows 1 class
(Actinobacteria), five subclasses, six orders, 14
suborders, 44 families
• consists of actinomycetes and their high G + C
gram-positive relatives
14
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Figure 22.6; representatives of genus
Actinomyces
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16
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Suborder Actinomycineae
• one family with five genera
• irregularly shaped, gram-positive rods
– swelling, club shapes, or other deviations from
normal rod morphology
• aerobic or facultative metabolism
17
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Genus Actinomyces
• straight or slightly curved rods and slender filaments
with true branching
– may have swollen, clubbed, or clavate ends
• facultative or obligate aerobes (require CO2)
• peptidoglycan contains lysine and not diaminopimelic
acid or glycine
• normal inhabits of oral mucosa
– cause of lumpy jaw in cattle
– ocular infection, actinomycoses, and peridontal disease in
humans
18
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Figure 22.7; Mycrococcus luteus stained with
methylene blue
19
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Suborder Micrococcineae Genus Micrococcus
• aerobic, catalase-positive rods that occur in
pairs, tetrads, or irregular clusters
• usually nonmotile
• often pigmented yellow, orange, or red
• widespread in soil, water, and on human skin
• does not undergo morphological differentiation
20
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Figure 22.8; the Rod-coccus growth cycle
21
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Genus Arthrobacter
• aerobic, catalase-positive rods, respiratory
• Have lysine in peptidoglycan
• rod-coccus growth cycle
– exponential phase
• irregular, branched rods
– reproduce by snapping division
• early stationary phase
– begin to change to coccoid form
• when transferred to fresh medium, coccoid cells
produce outgrowths of actively growing rods
22
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Genus Dermatophilus
• Dermatophilus (type IIIB)
– form packets of motile spores with tufts of
flagella
– facultative anaerobes
– parasites of mammals
• cause streptothrichosis – skin infection
23
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Suborder Corynebacterineae
• has seven families with many known
genera such as
– Corynebacterium
– Mycobacterium
– Nocardia
24
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Genus Corynebacterium
• aerobic and facultative, catalase positive
• straight to curved rods with tapered ends
and club shaped
• after snapping division bacteria often
remain partially attached resulting in
palisade (rows of cells are aligned side by
side) arrangements of cells
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Figure 22.9: Corynebacterium diphtheriae
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Figure 22.10; Mycobacterium
leprae
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Genus Corynebacterium
• form metachromatic granules
• cell walls have meso-diaminopimelic acid
• some are harmless soil and water
saprophytes
• many are animal and human pathogens
– e.g., C. diphtheriae - diphtheria
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Genus Mycobacterium
• in family Mycobacteriaceae
– straight or slightly curved rods that
sometimes branch or form filaments
• aerobic and catalase positive
• filaments readily fragment into rods and
coccoid bodies
• very slow growing on culture media
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Mycobacterial Cell Walls
• contain waxes with 60 to 90 carbon
mycolic acids
• cell wall surface
– consists of the glycolipid trehalose dimycolate
• once called cord factor
• cell wall very hydrophobic (due to long mycolic
acids)
• impenetrable by antibiotics that is why TB is very
hard to treat
– Stained by acid-fast
• basic fuchsin dye cannot be removed from cell by
acid alcohol treatment
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Figure 22.11; Mycolic acid structure
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Important Species of Mycobacterium
• M. bovis
– tuberculosis in cattle, humans
• M. tuberculosis
– tuberculosis in humans
• M. avium complex (MAC)
– various diseases
• M. leprae
– Leprosy in humans
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Genus Nocardia
• along with genus Rhodococcus make up
the family Nocardiaceae
• develop a substrate mycelium that readily
breaks into rods and coccoid elements
• some also form an aerial mycelium and
conidia
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Figure 22.12; Nocardia
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Figure 22.13; members of family
Micromonosporaceae
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Impact of Nocardia
• most are free-living saprophytes
– can degrade many molecules
• e.g., petroleum hydrocarbons, detergents, benzene
• involved in biodegradation of rubber joints in water
and sewage pipes
• some are opportunistic pathogens causing
nocardiosis.
– usually infect lungs; can also infect central
nervous system.
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Genus Rhodococcus
• widely distributed in soils and aquatic habitats
• degrade an enormous variety of molecules
such as
– petroleum hydrocarbons, detergents, benzene,
polychlorinated biphenyls (PCBs), various
pesticides
– may reduce sulfur from fuels and reduce air
pollution from sulfur oxide emissions
37
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Suborder Micromonosporineae
• Contains only one family,
Micromonosporaceae
–
–
–
–
extensive substrate mycelia
lack or have rudimentary aerial mycelia
sporangiospores motile or nonmotile
found in soil and aquatic habitats (especially
freshwater)
• soil dwellers play important roles in plant and
animal decomposition
• some produce antibiotics
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Genus Propionibacterium
• found on skin and in digestive tract of
animals
– also in dairy products such as cheese
– used in production of Swiss cheese
• e.g., P. acne – involved in development of
body odor and acne vulgaris
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Suborder Streptomycineae
• one family, three genera
• aerial hyphae that divide in single plane
to form chains of 3–50 nonmotile spores
• all have type I cell wall
• G+C DNA content is 69–78%
• filaments grow by tip extension
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Figure 22.15; Streptomyces
spore chains
Smooth spores
Spiney spores
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Watery spores
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Genus Streptomyces
• Make about 1 to 20% of culturable soil microbiota
– produce geosmin
• volatile substance that is source of moist earth odor (smelled when
it rains for the first time)
– important in mineralization process
• aerobically degrade many resistant substances (e.g., pectin, lignin,
and chitin)
• produce vast array of antibiotics, other bioactive
compounds, and antibiotic resistance genes
• most are nonpathogenic saprophytes
42
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Streptomyces coelicolor
• one of the largest bacterial genomes,
8.67 Mbp
– largest number of genes (7,825)
– 65 RNA polymerase sigma subunits
– 80 two-component regulatory systems
– Have genes for 18 additional secondary
metabolites
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Figure 22.14; Streptomyces development
S. colicolor
vegetative
hyphae with
branches
Chains of
S. colicolor spores
that will pinch off
and be released
into environment
44
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Pathogenic Streptomycetes
• Streptomyces scabies
– Cause scab disease in potatoes and
beets
• Streptomyces somaliensis
– Cause actinomycetoma
• infection of subcutaneous tissues in
humans
• leads to swelling, abscesses, and bone
destruction
45
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Figure 22.16
Streptomycin producing S. griseus
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S. Scabies grown on potato
Suborder Streptosporangineae
• three families, 16 genera
• aerial mycelia bear pairs or short chains
of spores
– whole cell homogenates contain sugar
madurose
• Actinomadura associated with the disease
acinomycetoma
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Figure 22.17; Maduromycetes morphology
48
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Suborder Frankineae
• genera Frankia and Geodermatophilus
– both form multilocular sporangia
characterized by clusters of spores
– both have type III cell walls
• Geodermatophilus
– type IIIC, motile spores, aerobic
• Frankia – type IIID, nonmotile spores,
microaerophile, fixes nitrogen, symbiotic with
nonleguminous plants
49
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Figure 22.18; Frankia
Multilocular sporangia and spores
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Infected plant nodules that have
Frankia which fixes nitrogen
for the plant
Genus Sporichthya
• Sporichthya
– lack substrate mycelium
– use holdfasts to anchor to substratum
– grow upward to form aerial mycelia
• release motile, flagellated conidia in presence of
water
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Order Bifidobacteriales
• one family and ten genera
• e.g., genera Falcivibrio and Gardnerella
– found in human genitourinary tract
– Gardnerella thought to be major cause of
vaginitis
• e.g., Bifidobacterium
– nonsporing rods
– found in mouth and intestinal tract of warmblooded animals, in sewage, and in insects
52
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e.g., Bifidobacterium bifidus
• pioneer colonizer of human intestinal
tract
• does not appear to be major cause of
disease
• Used as probiotic agent
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