By Karen Scott (@DrKarenScott)
When
the word geography is mentioned, microbiology is not always the first thought,
however this was probably the main focus throughout my PhD studies. Being able
to understand the microbiology of the environment can greatly assist in putting
together the bigger picture, especially where sustainable organic waste
management practises are concerned, as they rely ultimately on understanding the
mechanisms that control organic matter decay.
This study builds upon my
earlier findings on gully pot waste degradation
and enzyme activity (see my previous blog) assessing the effect of starch on degradation
rate and enzyme activity (α- and β-glucosidase) under mesophilic (moderate temperature typically between 20 and 45 °C) and thermophilic (relatively high temperature between 45 and 122 °C) conditions. A key focus was to assess how the enzymes potentially adapt to
different temperature regimes to assist in understanding whether the
effect observed was an
acclimatisation effect, or it is in fact a true temperature effect that is a
result of the composting
process. This reciprocal design measured
the differences between increased or decreased assay temperatures compared to the
temperatures the waste was composted
at. The enzyme activity was measured to assess
the degradation dynamics. The experiment
took place over a 6 week period where mesocosms (a mix of water and sieved gully
waste) were incubated under mesophilic (30ºC) and thermophilic (50ºC) conditions, a starch additive was added to half of these mesocosms.
The messy job - mixing the slurry ready for the experiment |
The
results for the enzyme activity did not follow the same suit, showing greater
activity in those that had the starch addition, confirming
that a starch addition
significantly increases the activity of both α- and β-glucosidase, albeit
weakly for the β-glucosidase. Whilst β-glucosidase activity
is on average higher with the higher assay temperatures, this
was
not statistically significant in this instance, indicating neither
in situ temperature or assay
temperature are significant explanatory variables. However, the
effect of increased activity of β-glucosidase with increasing temperature
is consistent with previous results. Interestingly, the interactive effect of
assay and in situ temperature on α-glucosidase activity is weakly
significant which
would be indicative of an adaptive effect of temperature on the
enzymes responsible for this activity.
Similar results were obtained when α-glucosidase activity was
investigated with the starch amended samples only. Therefore, the data for α-glucosidase
assay provides evidence for thermal adaptation
in this environmental system. The results presented here would
be consistent with α-glucosidase being under selection (in an evolutionary
context). Whilst α-glucosidase activity is
on average twice as high when assayed at 50ºC than 30ºC for the 50ºC
starch amended samples, it is only 20% higher when assayed at
30ºC as compared with 50ºC for the 30ºC starch amended samples. Therefore
it appears that as enzymes become adaptive to
increasingly high
temperatures, they become increasingly less adaptive at lower
temperatures.
The mean activity for b- and a-glucosidase over the sampling period. the labels for each bar shows the in situ temperature followed by the assay temperature. |
This study demonstrates a positive association
between enzyme
activity and its putative
substrate (starch) and also the effect
of temperature appears to have an
adaptive selective influence on enzyme activity. Examining these temperature variables provided a better understanding of the processes occurring and displaying the wastes ability to decompose, to a degree, under conditions similar to those that it would be subjected to if using ex situ management system. Whilst complete
agreement between enzyme activity and in situ degradation was not
observed, it does leave
scope for more investigation into enzyme parameters which could
potentially shed more light on these
issues.
The paper which this blog was based on can be found here
The paper which this blog was based on can be found here
Adams,
J. D. W. and Scott, K. M. (2013).
Enzymatic analyses demonstrate thermal adaptation of α-glucosidase activity in
starch amended gully waste. Bioresource
Technology 127(0): 231-235.
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