Microbial Degradation of Amino Acid-Containing Compounds Using the Microcystin-Degrading Bacterial Strain B-9

Abstract

Strain B-9, which has a 99% similarity to Sphingosinicella microcystinivorans strain Y2, is a Gram-negative bacterium with potential for use in the degradation of microcystin-related compounds and nodularin. We attempted to extend the application area of strain B-9 and applied it to mycotoxins produced by fungi. Among the tested mycotoxins, only ochratoxin A was completely hydrolyzed to provide the constituents ochratoxin α and l-phenylalanine, and levels of fumonisin B1 gradually decreased after 96 h. However, although drugs including antibiotics released into the aquatic environment were applied for microbial degradation using strain B-9, no degradation occurred. These results suggest that strain B-9 can only degrade amino acid-containing compounds. As expected, the tested compounds with amide and ester bonds, such as 3,4-dimethyl hippuric acid and 4-benzyl aspartate, were readily hydrolyzed by strain B-9, although the sulfonamides remained unchanged. The ester compounds were characteristically and rapidly hydrolyzed as soon as they came into contact with strain B-9. Furthermore, the degradation of amide and ester compounds with amino acids was not inhibited by the addition of ethylenediaminetetraacetic acid (EDTA), indicating that the responsible enzyme was not MlrC. These results suggest that strain B-9 possesses an additional hydrolytic enzyme that should be designated as MlrE, as well as an esterase.

Isolation of a Novel Microcystin-Degrading Bacterium and the Evolutionary Origin of mlr Gene Cluster

“…Up to now, only part of the mlr pathway for MC degradation has been clarified; other major genes, especially those involved in Adda degradation, have not been elucidated. Since the mlr gene cluster may have co-evolved with the GI, it is likely that other main genes involved in MC degradation are present on it [32,33]. The analyses of the GI may help discover new genes within this pathway and contribute to the clarification of the whole MC-degrading process.…”

Microcystin-Detoxifying Recombinant Saccharomyces cerevisiae Expressing the mlrA Gene from Sphingosinicella microcystinivorans B9

“…A codon-optimized version of the mlrA gene sequence from S. microcystinivoran s B9 strain was used in our study. S. microcystinivorans B9 has proved to be efficient in the natural degradation of microcystins, as well as showing the degradation of MCs with immobilized bacteria, and further activity for different amino acid-containing compounds during bacterial growth [ 29 , 30 , 31 ]. Other studies confirmed the potential of MC degradation by B9 strain as one of the most efficient among tested microorganisms, reducing 95% of the initial concentration of toxins (1.0 μg.mL −1 ) after 96 h of cultivation [ 20 ].…”

Complete Genome Sequence of a Microcystin-Degrading Bacterium, Sphingosinicella microcystinivorans Strain B-9

“…The mlrE and mlrF genes in strain B-9 were similar to the dipeptidase and D-aminoacylase of strain C-1 ( 11 ) and shared 90% and 91% identity to those of strain C-1, respectively. In our previous study, we elucidated that a putative protease MlrE, which hydrolyzes a peptide into amino acids, played a role in the final step of the microcystin-degrading pathway ( 18 ). The activity of MlrE was not inhibited by the chelating agent EDTA, suggesting that the responsible enzyme was not MlrC in the final step ( 4 ).…”