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Abstract
BackgroundCompost habitats sustain a vast ensemble of microbes that engender the degradation of cellulose, which is an important part of global carbon cycle. β-Glucosidase is the rate-limiting enzyme of degradation of cellulose. Thus, analysis of regulation of β-glucosidase gene expression in composting is beneficial to a better understanding of cellulose degradation mechanism. Genetic diversity and expression of β-glucosidase-producing microbial communities, and relationships of cellulose degradation, metabolic products and the relative enzyme activity during natural composting and inoculated composting were evaluated.ResultsCompared with natural composting, adding inoculation agent effectively improved the degradation of cellulose, and maintained high level of the carboxymethyl cellulose (CMCase) and β-glucosidase activities in thermophilic phase. Gene expression analysis showed that glycoside hydrolase family 1 (GH1) family of β-glucosidase genes contributed more to β-glucosidase activity in the later thermophilic phase in inoculated compost. In the cooling phase of natural compost, glycoside hydrolase family 3 (GH3) family of β-glucosidase genes contributed more to β-glucosidase activity. Intracellular β-glucosidase activity played a crucial role in the regulation of β-glucosidase gene expression, and upregulation or downregulation was also determined by extracellular concentration of glucose. At sufficiently high glucose concentrations, the functional microbial community in compost was altered, which may contribute to maintaining β-glucosidase activity despite the high glucose content.ConclusionThis research provides an ecological functional map of microorganisms involved in carbon metabolism in cattle manure–rice straw composting. The performance of the functional microbial groups in the two composting treatments is different, which is related to the cellulase activity and cellulose degradation, respectively.
Highlights
Compost habitats sustain a vast ensemble of microbes that engender the degradation of cellulose, which is an important part of global carbon cycle. β-Glucosidase is the rate-limiting enzyme of degradation of cellulose
For example, β-glucosidases are involved in cellulase induction and cellulose hydrolysis [10]. β-Glucosidases are mostly placed in either family 1 or family 3 of the glycosyl hydrolases, they are found in families 5, 9, and 30 of the glycosyl hydrolases [11,12,13]
Our results showed that high concentrations of glucose in natural compost were associated with a decrease in β-glucosidase activity (Fig. 4b), which is in accordance with the findings of previous researchers
Summary
Compost habitats sustain a vast ensemble of microbes that engender the degradation of cellulose, which is an important part of global carbon cycle. β-Glucosidase is the rate-limiting enzyme of degradation of cellulose. Β-Glucosidases, which are frequently very sensitive to the presence of glucose, one of the primary products of their catalytic activity [5,6,7], often play the rate-limiting role in cellulose degradation. Given the importance of cellulose degradation in providing carbon during the composting process, it is needful to understand the diversity, properties, and expression of the enzymes involved and to identify β-glucosidase enzymes that are insensitive to product inhibition by glucose. Β-Glucosidases are a heterogeneous group of phylogenetically conserved, hydrolytic enzymes widely distributed in the living world This enzyme family plays a pivotal role in several biological processes [9]. Most of the fungal β-glucosidases belong to family 3 of the glycosyl hydrolases [14]
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