Agriculture Reference
In-Depth Information
relative abundance of mesophilic bacterial strains from days 40-60 of composting,
suggesting that cellulase activity is mostly associated with thermophilic
Bacilli
;
however, many members of the order Bacillales are known to be thermoduric and
grow under thermophilic and mesophilic conditions. The composting of municipal
solid waste is reported by Castaldi et al. (
2008
). In their study, a decrease in cel-
lulase activity was observed during the first week followed by an increase in the
second week and again a decline after third week, finally becoming stable after 70
days. The β-glucosidase enzyme is a key component in the carbon cycle, the enzyme
catalyses the termination reactions of the glucose chains to release glucose. An in-
crease in β-glucosidase activity was observed during the first two weeks followed
by a sharp decrease until day 70, which stabilized over the course of the last month
of the process. The decrease in the activity of both cellulase and β-glucosidase dur-
ing the second part of composting could be attributed to an increase in the lignin
content and a gradual decrease in the availability of accessible cellulose content.
The authors indicated that change in enzyme activity is associated with a corre-
sponding change in organic matter content and microbial community succession
during the composting process. Raut et al. (
2008
) reported an increase in cellulase
activity that reached a maximum on day 12 of municipal sludge waste composting
(aerated with added glucose) followed by a decline in activity until the end of the
composting period (21 days). However, in the normal compost (without aeration) an
increase in cellulase activity until the end of the composting period (21 days) was
observed, indicating the availability of cellulose. The increase in cellulase activity
in normal compost corresponds to an increase in the biomass of thermophilic
Bacilli
towards the end of the composting period. Wei et al. (
2012
) used microbial rDNA
abundance as a tool to study the dynamics of microbial community change along
with their secreted enzymes involved in the composting of a mix of yellow poplar
wood-chips and mown lawn grass dippings (85:15 in dry-weight). The changes in
the compositional data of the composed materials indicated a 50 and 42 % decrease
in cellulose and total hemicellulose concentration, respectively, over a period of 27
weeks. During composting predominance in cellulase activity was observed in the
later stages (24 weeks). In contrast, the measured hemicellulase activities, mainly
α-arabinosidase and β-galactosidase, were higher in the earlier stages of compost-
ing (3 weeks). Parallel studies with light and fluorescence microscopy indicated the
exposure of cellulose on the surface of the woody substrates during the later stages
of the composting.
6.6.3
Other Enzymes Involved During Composting
Urease is involved in the hydrolysis of urea to ammonium and carbon dioxide and is
closely related to the nitrogen cycle. Castaldi et al. (
2008
) observed a strong correla-
tion between urease, protease and β-glucosidase activity. Urease activity increased
during the first 3 weeks of composting and was the highest on day 21, followed by
a steep decline in activity in the fourth week and then stabilized after 70 days of
composting. The initial increase in urease activity could be attributed to the avail-
