Agriculture Reference
In-Depth Information
showed that treatment with ligninolytic enzymes also affected the rates of transfer
of proteins during the process. The ability of the enzymes to adsorb and desorb from
surfaces within the compost pile were affected by the ratio of manganese peroxidase
to lignin peroxidase. More work is needed in such areas to clarify how such interac-
tions can be expected to affect composting processes.
3.2.1.6
Compost as a Source of Enzymes
Enzymes capable of breaking down different components of lignocellulosic bio-
mass have been the focus of intense research efforts directed toward the preparation
of cellulose-based liquid fuels and related chemicals (Taherzadeh and Karimi
2007
;
Viikari et al.
2012
). As might be expected, compost has served as a convenient
source from which researchers have isolated enzyme-producing biota for use in
such efforts. Recent work of this type was reported by Liu et al. (
2011
) and Harun
et al. (
2013
). In many cases, the obtained organisms have been further engineered
by recombinant technology to enhance the expression and activity of the resulting
enzymes (Liu et al.
2011
).
3.2.2
Bacterial Communities
There is increasing realization within the published literature that different species
of bacteria or fungi often co-exist in a seemingly synergistic manner within compost
mixtures. As noted by Lü et al. (
2012
), given the complexity of materials present
in a compost pile, it is not reasonable to expect that a single organism would be
able to supply all of the different kinds of enzymes needed for efficient and timely
biodegradation. Rather, biodegradation is typically brought about by communities
of organisms. For example, ligninolytic enzymes can be expected to promote access
to polysaccharides within a compostable mixture, allowing other microorganisms to
flourish and take care of other aspects of biodegradation (Feng et al.
2011
).
The word “community” suggests the possibility that certain species may ordinar-
ily tend to share the same environmental niche. Indeed, several recent studies have
suggested that relatively stable, synergistic groupings of biota tend to occur together
at different phases of composting (Huang et al.
2010
; Kausar et al.
2010
; Fontenelle
et al.
2011
; Reddy et al.
2011
; Xiao et al.
2011
; Eida et al.
2012
; Gladden et al.
2012
;
Lü et al.
2012
; Wei et al.
2012
; de Gannes et al.
2013
; Karadag et al.
2013
). In gen-
eral, the cited studies showed that the communities of bacteria and fungi dominating
each successive phase of composting tended to be distinct from each other.
Figure
3.2
gives an example of how microbial populations often rise and fall sub-
stantially during the course of composting (Xiao et al.
2011
). A compost mixture
comprising kitchen waste, leaves, grass, and small branches was shredded. Due to the
small batch sizes employed (20 kg) the temperature was able to be controlled primar-
ily by incubation settings. As shown, the higher temperature of incubation resulted in
