dissipation of labeled pyrene was detected at 55
C after 42 days of composting. The
active bacterial communities in the composting changed over time, showing a
distinct difference among different stages. α, β, γ Proteobacteria, and Actinobacteria
were detected mainly while involved in pyrene degradation at 38
C over 14 days of
composting. Streptomyces appeared to dominate the pyrene degradation at 55
C. β
and γ Proteobacteria and Actinobacteria were the dominant pyrene degraders at
70
C after 42 days of composting and at 38
C after 60 days of composting.
However, these results also indicate that instead of a specific key degrader more
complex communities may be involved during the degradation of pyrene.
Covino et al. (2016) assessed the microbial shifts during the decontamination of
creosote-treated wood by co-composting with agricultural wastes using two bulking
agents, grass cuttings (GC), and broiler litter (BL). GC composting was characterized by high microbial biomass growth in the early phases as suggested by phospholipid fatty acid analyses. Based on the 454-pyrosequencing results, fungi (mostly
Saccharomycetales) constituted an important portion of the microbial community,
and bacteria were characterized by rapid shifts (from Firmicutes (Bacilli) and
Actinobacteria to Proteobacteria). However, during BL composting, larger amounts
of prokaryotic and eukaryotic PLFA markers were observed during the cooling and
the maturation phases, which were dominated by Proteobacteria and the fungi
belonging to the Ascomycota and those putatively related to the Glomeromycota.
The role of fungi in the co-composting process has not been satisfactorily studied
yet. In addition to Saccharomycetales, the increase in the amounts of ligninolytic
fungi may occur in the composts in the later phases, too. These fungi are able, thanks
to their exoenzymes (peroxidases and laccases), to cause non-specific radical oxidation of organic contaminants (e.g., heavy PAHs) the biodegradation of which would
be very difficult otherwise (Harms et al. 2011; Kües 2015; Steffen et al. 2002). In
spite of that, some authors proved that the degradation of PAHs in contaminated
soils did not correlate directly with the detected activities of ligninolytic enzymes
(Eggen 1999). It is likely that the synergic metabolic cooperation between the
present microorganisms and ligninolytic fungi occurs in practice when the primary
products of oxidation by ligninolytic enzymes are further degraded by the present
microorganisms (Ahlawat et al. 2010; García-Delgado et al. 2015). However, some
authors draw attention to the danger of forming trace amounts of highly toxic
metabolites (such as chlorophenols) as a consequence of the degradation of chlorinated aromatic structures by ligninolytic enzymes (Laine et al. 1997; Morimoto and
Tatsumi 1997; Öberg et al. 1990).
An inexhaustible spectrum of organic substances with specific properties may be
used as organic substrates for co-composting. Analyses of their composition usually
concern only the basic parameters that are important for their composting (carbon,
nitrogen, and moisture contents) because a detailed analysis of their composition is
basically impossible in higher volumes. Naturally, this diversity is reflected in the
microbial communities that develop in the course of the degradation of these substrates. Because of this fact, the efforts to identify relevant organisms participating in
degradation of contaminants in the course of co-composting are a very demanding
task as the microorganisms may differ significantly on the basis of the used substrate.
23 Composting Practices for the Remediation of Matrices Contaminated by. . .
483
C after 42 days of composting. The
active bacterial communities in the composting changed over time, showing a
distinct difference among different stages. α, β, γ Proteobacteria, and Actinobacteria
were detected mainly while involved in pyrene degradation at 38
C over 14 days of
composting. Streptomyces appeared to dominate the pyrene degradation at 55
C. β
and γ Proteobacteria and Actinobacteria were the dominant pyrene degraders at
70
C after 42 days of composting and at 38
C after 60 days of composting.
However, these results also indicate that instead of a specific key degrader more
complex communities may be involved during the degradation of pyrene.
Covino et al. (2016) assessed the microbial shifts during the decontamination of
creosote-treated wood by co-composting with agricultural wastes using two bulking
agents, grass cuttings (GC), and broiler litter (BL). GC composting was characterized by high microbial biomass growth in the early phases as suggested by phospholipid fatty acid analyses. Based on the 454-pyrosequencing results, fungi (mostly
Saccharomycetales) constituted an important portion of the microbial community,
and bacteria were characterized by rapid shifts (from Firmicutes (Bacilli) and
Actinobacteria to Proteobacteria). However, during BL composting, larger amounts
of prokaryotic and eukaryotic PLFA markers were observed during the cooling and
the maturation phases, which were dominated by Proteobacteria and the fungi
belonging to the Ascomycota and those putatively related to the Glomeromycota.
The role of fungi in the co-composting process has not been satisfactorily studied
yet. In addition to Saccharomycetales, the increase in the amounts of ligninolytic
fungi may occur in the composts in the later phases, too. These fungi are able, thanks
to their exoenzymes (peroxidases and laccases), to cause non-specific radical oxidation of organic contaminants (e.g., heavy PAHs) the biodegradation of which would
be very difficult otherwise (Harms et al. 2011; Kües 2015; Steffen et al. 2002). In
spite of that, some authors proved that the degradation of PAHs in contaminated
soils did not correlate directly with the detected activities of ligninolytic enzymes
(Eggen 1999). It is likely that the synergic metabolic cooperation between the
present microorganisms and ligninolytic fungi occurs in practice when the primary
products of oxidation by ligninolytic enzymes are further degraded by the present
microorganisms (Ahlawat et al. 2010; García-Delgado et al. 2015). However, some
authors draw attention to the danger of forming trace amounts of highly toxic
metabolites (such as chlorophenols) as a consequence of the degradation of chlorinated aromatic structures by ligninolytic enzymes (Laine et al. 1997; Morimoto and
Tatsumi 1997; Öberg et al. 1990).
An inexhaustible spectrum of organic substances with specific properties may be
used as organic substrates for co-composting. Analyses of their composition usually
concern only the basic parameters that are important for their composting (carbon,
nitrogen, and moisture contents) because a detailed analysis of their composition is
basically impossible in higher volumes. Naturally, this diversity is reflected in the
microbial communities that develop in the course of the degradation of these substrates. Because of this fact, the efforts to identify relevant organisms participating in
degradation of contaminants in the course of co-composting are a very demanding
task as the microorganisms may differ significantly on the basis of the used substrate.
23 Composting Practices for the Remediation of Matrices Contaminated by. . .
483