Isolation Of A Strain Of Erwinia Sp. And The Study On The Characteristics Of Its Algicidal Effect

The incidence of harmful algal blooms(HABs) has recently increased in frequency as a long-term trend on a global scale. Algae-lysing bacteria that could kill bloom-forming phytoplankton have been isolated from the nature.lt is now thought, that those bacteria may terminate harmful algal blooms and regulate algal population dynamics in both freshwater and marine environments. The lytic effects of algae-lysing bacteria on their host cell may possibly be a factor in population dynamics of algae in nature and may contribute to the often-observed sudden disappearance of algal blooms in natural environments.Now,more attentions have focused on the issue that algae-lysing bacteria act as a possible factor to mitigate the adverse effects of HABs.Water samples were collected from the surface of seven eutrophic ponds in Wuhan city during the period from April, 2001 to September ,2002. The water samples were firstly pre-treated,Then modified infective methods in both liquid and agar media were carried out to isolate algae-lysing bacteria which can lyse or inhibit nine cyanobacteria presented in this paper. We have developed an efficient screening method for algae-lysing bacteria in freshwater. Four strains algae-lysing bacteria were obtained,and more studied were couducted on the strain M14 ,the followings are results.M14 was isolated from KHD(Kuang huan dao)pond in the decline of a cyanobc.cterial bloom. According to the studies on the major bacteriological characteristics, it was identified as a Erwinia.sp.The bacterium is Gram negative, straight rods. Many kinds of carbohydrates can be utilized,but no gas is produced. Gelatin can not be liquefied. Catalase is negative and arginine dihydralase and oxidase tests are positive.lt showed potent algicidal activity against filamentous cyanobacteria: Anabaena PCC7120, Anabaenasp 595. Plectonema boryanum IU594, Phormidiumfoyeolarum IU427, Scytonema hofmanni IU1581 and Nostoc sp 96 when we co-cultivated them,respectively. Bacterial culture filtrate experimentsshow that the bacterial strain M14 gives lethal effects on filamentous cyanobacteria by means of extracellular products. Preliminary study revealed that the strain could secrete some extracellular materials which are responsible for the algicidal activity from the stationary stage.We also studied the effect of some organic substances on M14 algicidal activity. The results showed that the growth of Anabaena sp 595 wasn't affected by some organic substances in moderate concentrations. The algicidal activity of M 14 could be promoted in the BG11 media supplemented with 0.5% peptone or 0.4% yeast extract.