Agriculture Reference
In-Depth Information
Hyper-thermophilic
bacteria and fungi
Hyperthermophilic
>65
o
C
Phase
60
Mesophilic
bacteria and
fungi
50
Thermophilic
Phase
40-65
o
C
Mesophilic actinomycetes, other bacteria,
and fungi predominate,
invertebrates colonize outdoor piles
40
Breakdown of complex lignocellulosic
substrates including cellulose, hemi-
cellulose,pectin, and fats
Mesophilic
Phase
Long, slow degradation of lignin and
other highly resistant compounds, and
formation of resistant organic mixture
called humus
Thermophilic bacteria and fungi,
dominated by members of order
Bacillales
30
Mesophilic
Phase
10-40
o
C
Exponential
growth, rapid
breakdown of
starches and
easily
biodegradable
polysaccharides
10-40
o
C
20
Cellulases, xylanases, mannanases,
pectinases
X
ylanases, mannanases, pectinases
Proteases,
Urease,
Amylases
10
Proteases,
Urease
Laccases,ligninases, phenol oxidases
30
03
10
15
18
Time (Days)
Fig. 6.1
A schematic illustration of the enzymes and microbial community prevailing during the
three different phases of composting (modified from cwmi.css.cornell.edu/chapter1.pdf)
ant bacterial strains from hot compost in Nepal. The isolates were presumptively
identified as
B. subtilis
,
B. licheniformis
,
Bacillus
sp.,
Geobacillus
sp., and
Paeni-
bacillus
sp., based on phenotypic and biochemical parameters. Highest activity on
carboxymethylcellulose (CMC) was observed with
B. subtilis
. The partially purified
enzyme was stable in the pH range 6.6-9.0 and showed optimum activity at pH 7.2
and 50 °C. Members of thermophilic
Bacilli
belonging to the genus
Bacillus
were
isolated and identified from garden compost at Rhodes University, Grahamstown
(Mayende et al.
2006
). The authors reported the presence of cellulases from
B. sub-
tilis
and
Bacillus
sp. that were found to perform optimally at 70 and 80 °C, respec-
tively.
Paenibacillus cookii
strain B39 was isolated and identified from poultry
manure compost in Taichung, Taiwan (Wang et al.
2008
). The cellulases from strain
B39 was purified using ion-exchange chromatography with a specific activity of
54.94 U/mg proteins. SDS-PAGE indicated the presence of a 148 kDa polypeptide;
activity staining was used to confirm the presence of cellulases. The optimum
CMCase activity was observed at 60 °C and pH 6.5. Substrate specificity studies
revealed that these cellulases could also hydrolyse Avicel and filter paper in addition
to CMC. The presence of Avicelase activity in bacterial cellulase is quite rare and
makes this cellulase important for industrial application. In the presence of calcium
ions the hydrolytic effect towards all the substrates was enhanced two-fold. The
enzyme was also found to be activated in the presence of copper ions but was inhib-
ited in presence of EDTA, HgCl
2
and SDS. Ng et al. (
2009
) reported the isolation of
over 100
Geobacillus
sp. strains from rice straw compost supplemented with pig
manure. The genomic library of
Geobacillus
sp. 70PC53 was screened for presence
