ABSTRACT
This report describes the whole-genome sequence of an alkalitolerant microcystin-degrading bacterium, Sphingopyxis sp. strain C-1, isolated from a lake in China.
ABSTRACT
The mlr gene cluster consisting of mlrA, mlrB, mlrC, and mlrD is involved in the degradation of the cyanobacterial toxin microcystin. However, it is unclear which degradation intermediates are metabolized by MlrB and MlrC. To address these questions, we constructed recombinant Escherichia coli to overproduce MlrB and MlrC from Sphingopyxis sp. C-1, and determined which intermediates were degraded in cell-free extracts. The cell-free extract containing MlrB degraded linearized microcystin-LR, giving rise to a tetrapeptide. The cell-free extract of MlrC degraded linearized microcystin-LR and also degraded the tetrapeptide to the amino acid Adda. These results indicate that linearized microcystin-LR is degraded by both MlrB and MlrC, and tetrapeptide is degraded by specifically by MlrC in Sphingopyxis sp. C-1.
Subject(s)
Bacterial Proteins/metabolism , Bacterial Toxins/metabolism , Marine Toxins/metabolism , Microcystins/metabolism , Sphingomonadaceae/enzymology , Sphingomonadaceae/metabolism , Bacterial Proteins/genetics , Bacterial Toxins/chemistry , Biodegradation, Environmental , Cyanobacteria Toxins , Escherichia coli/genetics , Escherichia coli/metabolism , Genes, Bacterial , Marine Toxins/chemistry , Microcystins/chemistry , Multigene Family/genetics , Proteolysis , Sphingomonadaceae/geneticsABSTRACT
The pH of the water associated with toxic blooms of cyanobacteria is typically in the alkaline range; however, previously only microcystin-degrading bacteria growing in neutral pH conditions have been isolated. Therefore, we sought to isolate and characterize an alkali-tolerant microcystin-degrading bacterium from a water bloom using microcystin-LR. Analysis of the 16S rRNA gene sequence revealed that the isolated bacterium belonged to the genus Sphingopyxis, and the strain was named C-1. Sphingopyxis sp. C-1 can grow; at pH 11.0; however, the optimum pH for growth was pH 7.0. The microcystin degradation activity of the bacterium was the greatest between pH 6.52 and pH 8.45 but was also detected at pH 10.0. The mlrA homolog encoding the microcystin-degrading enzyme in the C-1 strain was conserved. We concluded that alkali-tolerant microcystin-degrading bacterium played a key role in triggering the rapid degradation of microcystin, leading to the disappearance of toxic water blooms in aquatic environments.
