Biodegradation of microcystin-LR by an amino acid-degrading anaerobic bacterium

Abstract

A B S T R A C TRecent studies have proved that microcystins (MCs) can be degraded by sediment under anaerobic conditions, suggesting that anaerobic biodegradation is an important pathway to remove MCs in water treatment. In this study, the potential for biodegradation of microcystin-LR (MCLR) by an amino acid-degrading anaerobic bacterium ALA-1 was investigated. Under mesophilic conditions (20, 25 and 30˚C), MCLR was dropped from 4 mg/L to below the detection limit in 10 d without lag phase. While at cold temperatures (10 and 15˚C), MCLR degraded completely in 14 and 19 d with a delay time reaching 6 and 8 d, respectively. Under alkaline conditions (pH 8.0, 9.0), MCLR was degraded completely within 10 d without a lag phase. While MCLR was degraded completely within 12 d under neutral condition (pH 7.0). A lag time of 8 and 20 d was needed prior to the onset of MCLR degradation under two slightly acidic conditions (pH 6.0, 5.0), respectively, and MCLR was completely consumed until day 22 and day 38. In addition, extra carbon or nitrogen sources had no significant effect on the degradation ability of ALA-1. Linearized MCLR (m/z 1,013.3729, C 49 H 77 N 10 O 13 ), tetrapeptide (m/z 616.1208, C 32 H 48 N 4 O 8 ) and Adda (m/z 332.0186, C 20 H 30 NO 3 ), commonly known as aerobic biodegradation products of MCLR, were detected as the intermediate products. The mlrA gene homologue, known for its degradation potential of MCLR, was absent in strain ALA-1, implying that other enzymes which were not encoded by the mlrA gene cluster might have been involved in metabolizing MCLR in the present study.

Effects of Microcystin-LR on Metabolic Functions and Structure Succession of Sediment Bacterial Community under Anaerobic Conditions

“…YF3 with the maximum degradation rate of 0.34 mg/L/day under the optimal condition (37 • C, pH = 7, 5 mg/L MC-LR) [34]. Bao and Wu found that amino acid-degrading anaerobic bacterium ALA-1 had greater degrading ability under mesophilic and alkaline conditions than cold, neutral, and slightly acidic conditions [35]. Zhu et al deduced that Candidatus Cloacamonas acidaminovorans Evry may degrade MC-LR under anaerobic conditions through microbial community analysis [36].…”

“…Chen et al found that MC-LR could be degraded by lake sediments under anoxic conditions with the production of final product Adda [25]. Linearized MC-LR, tetrapeptide, and adda, known as aerobic degradation products of MC-LR, were also produced by bacterium ALA-1 [35]. Two new linearized MC-LR, Ala-Leu-MeAsp-Arg-Adda-Glu-Mdha and Leu-MeAsp-Arg-Adda-Glu-Mdha-Ala, were detected in the degradation products of MC-LR, proving that new degradation pathways exit in anaerobic MC-degrading bacteria through hydrolyzing peptide bonds at Ala-Mdha and Ala-Leu [36,59].…”

Microcystins in Water: Detection, Microbial Degradation Strategies, and Mechanisms

“…However, the degradation rates of MCs were found to be higher under anaerobic conditions [ 76 ]. The degradation potential of the amino acid anaerobic strain ALA-1 for MC-LR was demonstrated by Bao et al This strain was able to degrade 4 mg/L MC-LR to levels below the detection limit within 10 days at moderate temperatures without a lag period [ 77 ]. An analysis of MCs in cyanobacterial cells and the biodegradation of MC-YR, -RR, and -LR by Sphingomonas sp.…”

Simultaneous Removal of the Freshwater Bloom-Forming Cyanobacterium Microcystis and Cyanotoxin Microcystins via Combined Use of Algicidal Bacterial Filtrate and the Microcystin-Degrading Enzymatic Agent, MlrA

“…The genetic and enzymatic mechanism of the Microcystinase (Mlr)-dependent pathway for MC biodegradation was fully described, in which MC is degraded sequentially into linearized MC, tetrapeptides, Adda, phenylacetic acid, and ultimately, CO 2 , via a series of specific enzymes encoded by mlr and neighboring paa gene clusters [ 25 , 26 , 27 ]. The mlr -dependent degradative activity of indigenous bacteria is under strict control and is affected by multiple factors [ 28 , 29 , 30 ]. Therefore, the direct modulation of wild MC-degraders in practical applications remains a challenge.…”