Detection And Bio-control Of Harmful Cyanobacteria In Queshan Reservoir

Harmful cyanobacteria that produce cyanotoxins or odorous compounds have affected water system seriously and threaten human health. It is of great significance to conduct researches on rapid detection and effective control of harmful cyanobacteria. Given that method for detection of cyanotoxins-producing cyanobacteria has been established previously, in the present, the detection of harmful algae was focused on the odor-synthesis gene of the algae. In addition, researches on bio-control of cyanobacteria were conducted using algicidal bacteria and bio-flocculant.The main odorous compounds of geosmin and2-methylisoborneol (2-MIB) were detected during monitoring using solid-phase microextraction combined with gas chromatography mass spectrometry (SPME-GC/MS) in the Queshan reservoir. Moreover,2-MIB is frequently detected in the test period. Through T-A clone and sequence analysis, it was found that gene for synthesis of odor compounds existed in the Queshan reservoir, thus could be used for the detection of odor-producing algae..About37algicidal bacteria strains were isolated from environment samples. Among these,29strains were obtained from LB medium and the other8strains from R2A medium. The algicidal bacteria could effectively lyse the cyanotoxins-producing M.aeruginosa975, geosmin-producing Oscillatoria sp.528and2-MIB producing Pseudanabaena sp.1277. Culture conditions have effect on algicidal activity. Moreover, algicidal activity increased as the initial concentration of bacteria increased, with more than85%alga being removed by initial2×108cells/mL bacterium. The algicidal effects of the isolated bacteria against alga worked via its extracellular substances. Further studies showed that the extracellular substances associated with anti-cyanobacterial effect were heat stable and non-protein. Moreover the algicide showed strong inhibition against other cyanobacteria such as A. spiroides498, P. agardhii920and O. tenuis1052. The algicidal bacteria have potential for alga removal.An algicidal bacterium of Aeromonas sp. FM was isolated from Queshan reservoir previously. In the present study, it was found that strain FM inhibited the growth of M. aeruginosa975, Oscillatoria sp.528and Pseudanabaena sp.1277. The secretion of extracellular soluble carbohydrates by M. aeruginosa975(ESC) was promoted after the extracellular substances of strain FM (ES-FM) added. The production of extracellular soluble carbohydrates increased as the dosage of extracellular substances increased. Adjusting of pH in the mixture changed the production of extracellular substances. The extracellular soluble carbohydrates showed significant flocculating activity to kaolin suspension and the activity was affected by flocculant dosage, pH and cation type. The addition of0.38mg/L ESC prepared from M. aeruginosa under treatment of ES-FM resulted in a flocculating activity of88.5%for kaolin suspension at pH10. Significant flocculation of M. aeruginosa cells occurred after8mg/L ES-FM was added to cultures of M. aeruginosa. Therefore, the ESC secreted by M. aeruginosa cells has potential for application in cyanobacteria removal.