Download How the decomposers decompose: mineralization of microbial

How the decomposers decompose:
Lorraine C. Murtagh
Mineralization of microbial carbon and nitrogen in soils
Why microbial C and N?
• To understand more about soil N we need to
D- and L- amino acids are
mineralized at different rates
consider microbial structural N because this is
one of the least well understood components
• To understand more about the mineralization of
C
respired
(mg g-1
soil)
School of Biological &
Environmental Sciences,
University of Stirling
Isotopic labelling
Conclusions
• 13C-labelled D- and L-alanine were added to soil which
• No intermediate compounds identified in liquid-
was frozen at 0, 24, 72 and 150 hrs. Alkali traps were
state NMR analysis for D- or L-alanine: this
used to capture respired CO2. Water soluble and clay-
suggested no major differences between the
adsorbed fractions were analysed by liquid-state NMR.
mechanisms of mineralization
this N we can look at the mineralization of C
Mass spectroscopy was used to determine the amount of
• However there is a higher activation energy for
from these compounds
13C
the mineralization of D- than for L-amino acids:
C
respired
(mg g-1
soil)
present in the soil and CO2.
• This allowed a picture to be built of where the 13C was
D- and L-forms are likely broken down by the
located at various time periods, and in what compounds
same mechanism but it takes more energy to
• Microorganisms contain a diverse range of N-
• No new compounds were identified by liquid-state
break down D-forms. Therefore there is a delay in
containing structural compounds, such as amino
NMR, just a typical signal for alanine. The intensity of
mineralization of D- compared to L-amino acids
the signal decreased over time, more rapidly so for L-
• Land use does not affect the relative
alanine
mineralization kinetics of D- and L-amino acids
Why amino acids?
acids
• Amino acids are relatively simple compounds
Figure 2. Substrate-induced respiration with D- and L-amino
acids in two soils under two land uses. Respiration was
initially faster in each case with the L- form but by
approximately 150 hours, the amount of C respired with the Dform caught up
and are readily metabolised by microorganisms in
the soil
• D-alanine and D-glutamic acid are the most
Further Work
Kinetics of mineralization
Distribution of
• Substrate-induced respiration rates at a range of
common microbial amino acids
• Previous work has shown differences in C
mineralization rates between microbial and nonmicrobial amino acids - Why is this?
temperatures were used to calculate the activation energy
of the mineralization of D- and L-amino acids using the
relationship between the rate and the temperature
% of
mechanism not identified by liquid-state NMR
60%
• Investigation of the effects of fertiliser nitrogen
13
C
40%
added
on the mineralization of D- and L-amino acids
20%
0%
D-glutamic L-glutamic
acid
acid
Gleneagles 83.99
28.75
arable
Gleneagles 67.26
31.64
grass
Stirling
77.84
29.86
arable
Stirling
81.72
34.09
grass
• D-glutamic acid had a higher activation energy than L-
L-amino acids  all organisms
glutamic acid in each case. There were no effects due to
D-amino acids  bacteria
either the soil type or the land-use
24
72 150
Gleneagles
arable
0
24
72 150
Gleneagles
grass
0
24
72 150
Stirling
arable
0
24
72 150
Stirling
grass
Time (hours)
In soil
Adsorbed to clay particles
Water soluble
Respired
• Investigation of the impacts of D- and L-amino
acids on the activities of enzymes in soil
Acknowledgements
L-alanine
100%
Thanks to: David Hopkins, Charlie Scrimgeour, Susan
Mitchell and Ron Wheatley from SCRI; Sandy Chudek and
Gina Mackay from the University of Dundee
Funding was provided by the Biotechnology and Biological
Sciences Research Council (BBSRC)
80%
% of
• Solid-state NMR analysis of soil is yet to be
completed – this may identify differences in
80%
0
Figure 1.
Structure of Dand L-forms of
amino acids.
These are
stereoisomers –
i.e. nonsuperimposable
mirror-images of
each other.
over time
D-alanine
100%
Table 1. Activation energy (kJ mol-1) of substrate-induced
respiration with D- and L-glutamic acid in four soils
Amino acid structure
13C
60%
13
C
40%
added
Contact details
20%
0%
0
24
72 150
Gleneagles
arable
0
24
72 150
Gleneagles
grass
0
24
72 150
Stirling
arable
Time (hours)
0
24
72 150
Stirling
grass
Figure 3. Distribution of 13C added as D- or L-alanine over a
period of 0-150 hrs. 13C respired as CO2 increased over time,
while 13C in the water soluble fraction of the soil, adsorbed to
clay particles and in the soil itself decreased over time. This
process occurred more rapidly with L-alanine than D-alanine
Lorraine Murtagh, School of Biological and Environmental
Sciences, University of Stirling, Stirling, FK9 4LA,
Scotland, UK. Email: [email protected]