Mechanism of differential expression of β-glucosidase genes in functional microbial communities in response to carbon catabolite repression

Background β-Glucosidase is the rate-limiting enzyme of cellulose degradation. It has been stipulated and established that β-glucosidase-producing microbial communities differentially regulate the expression of glucose/non-glucose tolerant β-glucosidase genes. However, it is still unknown if this differential expression of functional microbial community happens accidentally or as a general regulatory mechanism, and of what biological significance it has. To investigate the composition and function of microbial communities and how they respond to different carbon metabolism pressures and the transcriptional regulation of functional genes, the different carbon metabolism pressure was constructed by setting up the static chamber during composting. Results The composition and function of functional microbial communities demonstrated different behaviors under the carbon metabolism pressure. Functional microbial community up-regulated glucose tolerant β-glucosidase genes expression to maintain the carbon metabolism rate by enhancing the transglycosylation activity of β-glucosidase to compensate for the decrease of hydrolysis activity under carbon catabolite repression (CCR). Micrococcales play a vital role in the resistance of functional microbial community under CCR. The transcription regulation of GH1 family β-glucosidase genes from Proteobacteria showed more obvious inhibition than other phyla under CCR. Conclusion Microbial functional communities differentially regulate the expression of glucose/non-glucose tolerant β-glucosidase genes under CCR, which is a general regulatory mechanism, not accidental. Furthermore, the differentially expressed β-glucosidase gene exhibited species characteristics at the phylogenetic level.

β-glucosidase genes differentially expressed during composting

Background: Cellulose degradation by cellulase is brought about by complex communities of interacting microorganism, which significantly to the cycling of carbon on a global scale. β-Glucosidase is the rate-limiting enzyme of degradation of cellulose. Thus, analysis of expression of genes involved in cellulose degradation and regulation of β-glucosidase gene expression in composting is beneficial to a better understanding of cellulose degradation mechanism. According to our previous researches, we present the hypothesis that “microbial functional communities differentially regulate the expression of glucose-tolerant β-glucosidase and glucose sensitive β-glucosidase (up or down regulation) to adapt to the changes in cellulose degradation.” Results: Here, the functional microbial community structure and function change in association with cellulose degradation during the process of natural and inoculated composts was investigated by metatranscriptome and DNA clone library. Compared with inoculated compost, cellulose degradation was obviously inhibited during natural composting. Especially, the cooling phase of natural compost exhibited carbon catabolite repression (CCR) effect due to high concentration of glucose and cellobiose. The expression of genes encoding endoglucanase and exoglucanase were significantly down-regulation, while the CCR has no effect on β-glucosidase genes expression levels. But functional microbial community composition changed significantly, the composition of glucose-tolerant β-glucosidase increased. Conclusions: These results indicated that microbial functional communities differentially regulate the expression of glucose tolerant β-glucosidase (up regulation) and non-glucose tolerant β-glucosidase (down regulation) under CCR. This work provides a frame work to predict how functional microbial communities will respond to cellulose degradation conditions changes.

Performance, process kinetics and functional microbial community of biocatalyzed electrolysis-assisted anaerobic baffled reactor treating carbohydrate-containing wastewater

The microbial electrolysis cell and dynamic model have been applied to improve methane production and achieve the optimal regulation of a thermophilic ABR system; the effective performance was due to a synergy effect of functional microbes.