Isolation and identification of a native bacterium Citrobacter farmeri against microcystin-LR in anaerobic environments.

Abstract

Microcystin-LR (MC-LR), produced by cyanobacterial harmful algal blooms, poses a serious threat to aquatic ecosystems and human health. Biodegradation is an important method for MC-LR elimination. Aerobic biodegradation has been extensively studied and many bacteria were identified. However, few MC-degrading bacteria have been isolated from anaerobic environments, and these degradation mechanisms are poorly understood. The aim of this study was to collect anaerobic MC-degrading bacteria from lake sediments in Lake Taihu using acclimation culture to assess biodegradation. Five strains with MC-LR degradation ability were isolated, with strain A4 belonging to Citrobacter farmeri (C. farmeri). exhibiting the highest efficiency at 0.486 μg/ml/d. High-performance liquid chromatography (HPLC) identified two novel MC-LR degradation products. Further polymerase chain reaction (PCR) analysis suggested that C. farmeri A4 did not possess the known MC-degrading gene mlrABCD, suggesting the involvement of an mlrABCD-independent anaerobic degradation pathway. Data demonstrated that the bacterial strain C. farmeri A4 found in Lake Taihu exhibited high anaerobic MC-LR degradation properties, which indicated that anaerobic biodegradation may constitute an important biological method for MC-LR removal in natural environment.