Screening, Identification Of A Microcystins Degrading Bacteria Strain And Its Activity For The Biodegradation Of Microcystins

In this paper, a series of studies about microcystins pollution in Chaohu water body were carried.In the research fields of cyanobacteria toxins, the demanding for microcystins is increasing. As known, the relative content of the MCs in the algal cells is low, and the interferencing of other material is enomous, and the separation and purification cost is high. So, the rapid, efficient, low-cost extraction methods of MCs are particularly essential. However, there are various means to purify MCs according to the different needs of researchers. There is not a standard way so far.In this study, the preservation and extraction of MCs have been improved from many aspacts such as the cyanobacteria preserving, the cell disrupting, the extractation solvent system of the MCs, the extractation time of MCs.The efficient bacteria of degradating microcystins had been screened, isolated and identified, and their ability for degradating microcystins in different environmental conditions had been studied.The results showed that the main microcystins in Chaohu Lake are MC-RR and MC-LR, and the MC-RR is the most type. The five bacteria which could biodegrade microcystins were screened from the sediment of Chaohu Lake. The MCs extracted and purified from Chao Lake was used as the only carbon and nitrogen source of the screening medium. Experimental results showed that the strain M9 had the highest degrading capacity, and strain M9 was identified as kurthia gibsonii strain by the biochemical and molecular identification.In order to investigate the efficiency of M9 strain for degrading MCs, environmental factors such as carbon sources, nitrogen sources, metalions and pH which may influence the degrading efficiency were studied. The experimental results provide a theoretical basis for the removal of algal toxins from eutrophication water.The strains M9 showed the strongest degradation capacity for MCs with 10 g/L of glycerol as a carbon source, and the maximum degradation rate of MC-RR and MC-LR was 88.8%and 79.5%in the 3 d, respectively. Comparing with the control, the maximum degradation rates of MC-RR and the MC-LR was 19.2%and 19.0%, respectively. The maximum degradation rate of MC-RR and MC-LR was 81.3%and 79.9%within 3 d, respectively with 1 g/L ammonium sulfate. Comparing with the control, the maximum degradation rate of MC-RR and MC-LR was 10.3%and 11.1%, respectively. At pH 7.0, the maximum degradation rate of MC-RR and MC-LR was 53.6%and 54.4%within 3 d, respectively. However, the maximum degradation rate of MC-RR and MC-LR was only 22.7%and 15.3%, respectively at pH5.0. The Zn2+ and Fe3+cound promoted the growth of strain M9, and the role of Zn2+is the most significant. The maximum degradation rate of the MC-RR and MC-LR was 52.4% and 49.4%within 3 d, and comparing with the control, the maximum degradation rate of MC-RR and MC-LR was 23.0%and 24.0%, respectively. The results indicated that the growth of strains M9 and the degradation for the MCs were significantly increased comparing with the control under the conditions of 10 g/L of glycerol,1 g/ L of ammonium sulfate, pH 7.0 and 1 mg/L Zn2+.