Exogenous glucose as the potential energy fuel stimulates the microcystin-LR degradation of Sphingosinicella microcystinivorans Y2

Abstract

External carbon sources have been recognized to affect the microbial-mediated remediation of microcystin (MC) in both natural and industrial polluted water bodies; however, the underlying molecular mechanisms remain unclear but would be worthy of further study. In this case, the MC-degrading bacterium, Sphingosinicella microcystinivorans Y2, was used to investigate the effect of exogenous glucose on MC biodegradation and its potential regulatory mechanisms. Our phenotypic results indicated that external glucose, within specific concentration ranges (125, 500, and 1000 mg/L), substantially accelerated the efficiency of MC degradation. Additionally, morphological observations suggested that glucose may positively impact the bacterial cells. A genome-oriented analysis of S. microcystinivorans Y2 was conducted to identify several Mlr-dependent MC-degrading genes, which were involved in the complete degradation of MC. Enrichment analysis of differentially expressed genes further indicated that glucose-promoted MC biodegradation may be associated with various biological processes. Furthermore, the gene-gene interaction network revealed the co-expression of genes mlrA and nadD, suggesting that increased levels of NAD⁺ may positively stimulate various biochemical reactions to fuel the MC degradation of strain Y2. In short, our findings present that exogenous glucose might accelerate the bacterial-mediated MC biodegradation, and further reveal its underlying molecular mechanisms, which provides the theoretical basis for the application of external carbon in the microbial treatment of toxic MC.