The effects and possible mechanisms of action of L- phenylalanine on the growth of Microcystis aeruginosa cells were explored by cell counting and flow cytometry assays. L- phenylalanine promoted the growth of Microcystis aeruginosa at concentrations between 0.078 and 0. 312 μg/mL, but inhibited growth at concentrations between 0. 625 and 20μg/mL in 24 h exposure. The dose-effect and time-course relationships between exposure to L-phenylalanine and growth inhibition of Microcystis aeruginosa were observed. The IC50 value of L-phenylalanine for growth inhibition of Microcystis aeruginosa was 6. 2 μg/mL （95% confidence interval was 0. 005 to 16. 76 μg/mL）. The membrane integrity of the cells showed significant variations after 24 h exposure to L-phenylalanine. Meanwhile, no effects on esterase activity of the cells were observed until after 48 h exposure to L-phenylalanine. In conclusion, L-phenylalanine has hormesis effects and algae control effects on Microcystis aeruginosa. The latter is closely related to alterations or disorders in the cell membrane and with variation of esterase activity in the cells.
Objective To isolate and characterize indigenous algicidal bacteria and their algae-lysing compounds active against Microcystis aeruginosa, strains TH1, TH2, and FACHB 905. Methods The bacteria were identified using the Biolog automated microbial identification system and 16S rDNA sequence analysis. The algae-lysing compounds were isolated and purified by silica gel column chromatography and reverse-phase high performance liquid chromatography. Their structures were confirmed by Nuclear Magnetic Resonance （NMR） and Fourier Transform infrared （FT-IR） spectroscopy. Algae-lysing activity was observed using microscopy. Results The algae-lysing bacterium LTH-2 isolated from Lake Taihu was identified as Serratia marcescens. Strain LTH-2 secreted a red pigment identified as prodigiosin （C20H25N30）, which showed strong lytic activity with algal strains M. aeruginoso TH1, TH2, and FACHB 905 in a concentration-dependent manner. The 50% inhibitory concentration （ICs0） of prodigiosin with the algal strains was 4.8 （±0.4）×10^-2 μg/mL, 8.9 （±1.1）×10^-2μg/mL, and 1.7 （±0.1）×10^-1 μg/mL in 24 h, respectively. Conclusion The bacterium LTH-2 and its pigment related to damage of cell membranes. The bacterium for regulating blooms of harmful M. aeruginosa. had strong Microcystis-lysing activity probably LTH-2 and its red pigment are potentially useful
YANG FeiWEI Hai YanLI Xiao QinLI Yun HuiLI Xiao BoYIN Li HongPU Yue Pu
The variations of environmental abundance and microcystin-LR （MC-LR） production ability of toxic Microcystis in the Nanquan region of Lake Taihu are investigated by real-time quantitative PCR （RTQ-PCR） and high performance liquid chromatography （HPLC） from May to December in 2009. Simultaneously, degrees of water pollution and eutrophication are monitored. The results indicate that the water quality in the Nanquan region of Lake Taihu is in a moderate degree of pollution and eutrophication. Algal density exceeds the threshold of bloom from May to November. The environmental abundance of toxic Microcystis is more than 40% from May to October and then significantly declines to 5.66% due to the obvious reduction in the water temperature in December. From May to December, the MC-LR production ability of toxic Microcystis ranges from 1.661 to 9.293 μg/108cells. With the significant drops in water temperature and algal density, the MC-LR production ability of toxic Microcystis is obviously increased from November to December. It is concluded that the lake presents Microcystis bloom and the toxic Microcystis becomes dominant during most of the year. The environmental abundance and the MC-LR production ability of toxic Microcystis have a close relationship with water temperature. The effective control of toxic Microcystis should be considered in both the bloom period and the non-bloom period of winter since the MC-LR production ability of toxic Microcystis obviously increases in winter.
The indigenous bacterial strain MC-LTH11 with the capability of degrading microcystin-RR MC-RR and microcystin-LR MC-LR was successfully isolated from Lake Taihu.The bacterium was identified as Stenotrophomonas sp. which possessed a mlrA gene. The MC-LTH11 thoroughly degraded MC-RR and MC-LR with the initial concentration of 37.13 mg/L and 18.49 mg /L respectively in the medium containing crude microcystins extract within 6 d.The degradation rates were affected by temperature pH initial MCs concentration and the kinds of media. Additionally the bacterial strain MC-LTH11 also degraded thoroughly microcystins in the water body of Lake Taihu within 1 d.These results suggest that the Stenotrophomonas sp.MC-LTH11 has the capacity to bioremediate water bodies contaminated by microcystins and may contribute to the degradation of microcystins after the outbreak of harmful cyanobacterial blooms in Lake Taihu.
