Microcystin-LR Biodegradation by Bacillus sp.: Reaction Rates and Possible Genes Involved in the Degradation

Abstract

Abstract:Harmful cyanobacteria blooms may deteriorate freshwater environments, leading to bad water quality that can adversely affect the health of humans, animals, and aquatic life. Many cyanobacteria can produce toxic metabolites, with Microcystin-LR (MC-LR) being the most commonly detected cyanotoxin in fresh water bodies. In this study, a MC-LR degrading Bacillus sp. strain was isolated from Hulupi Lake (HLPL), Taiwan and tested for its degradability of the cyanotoxin. The results showed that the degradation of Microcystin-LR by the isolated Bacillus sp. was temperature-dependent with an optimum MC-LR removal at 37 • C and a first order degradation constant rate for 0.22 day −1 . The degradation rate was also found to increase with decreasing MC-LR concentrations and increasing Bacillus sp. concentrations. Biomolecular monitoring of three types of genes (mlrA, CAAX, and GST) involved in the degradation indicated that mlrA, and CAAX genes were present in the indigenous bacteria in HLPL water samples. However, for the isolated Bacillus sp. strain, only CAAX genes were detected. The absence of the mlrA gene in the isolated Bacillus sp. strain shows that the degradation of MC-LR does not necessarily follow the pathways with mlrA, and can also follow the pathways involved with CAAX type II amino-terminal protease.

Impacts of Hydrogen Peroxide and Copper Sulfate on the Control of Microcystis aeruginosa and MC-LR and the Inhibition of MC-LR Degrading Bacterium Bacillus sp.

“…bacteria were obtained from a previous study [12] for MC-LR degrading bacteria isolation [41]. An amount of 100 mL Luria-Bertani (LB) broth (Sigma-Aldrich, Steinheim, Germany) was used to grow the isolated colonies of Bacillus sp.…”

“…ALX-850-319-KI01, Enzo Life Sciences Inc., Farmingdale, NY, USA). The measurements were made according to the method described by Fischer et al (2001) [47], and the absorbance read at 450 nm (Thermo Scientific™ Multiskan™ GO Microplate Spectrophotometer 357, Vantaa, Finland) against a calibration curve described in a previous study [12] with a MC-LR detection limit of 0.1 µg·L −1 .…”

“…To compare the degradation capability of these two algaecides on MC-LR with that from bacteria, a biodegradation experiment of MC-LR similar to that in Kansole and Lin (2016) [12] was conducted. In that experiment, MC-LR concentration was also chosen to be 0.05 mg·L −1 and 0.02 mg·L −1 , Bacillus sp.…”

“…Effective MC removal in water treatment plants (WTPs) is usually carried out via nanofiltration [7], oxidation [8], activated carbon [9] and biodegradation [10]. Among these processes, biodegradation usually takes place in sand filters in WTPs [11], and may also happen in natural water environments involving a variety of bacteria [12,13]. Among the MC degrading bacteria, Bacillus sp.…”

“…Among the MC degrading bacteria, Bacillus sp. [12,14] has been reported to be especially effective, with more than 80% removal of 15 mg·L −1 MC-LR reached within nine days' incubation [14].…”