Isolation And Identification Of One Algae-Lysing Bacteria And The Lytic Effects On Two Blue-Green Algae In Prawn Pond

Spraw aquaculture is one of the important industry in the economy of agricultural production in our country. During the spraw culture, the accumulation of organics and inorganics cause the excessive growth of some harmful algae. In the eutrophic aquaculture water, harmful algae can emerge some toxic substances (algae toxins)and severely damaged water environment. The serious problem is that the toxic substances immediately dangerous to raising animals. At present, improving spraw farming ecological environment and promoting the healthy and stability development of prawn culture has become a common concern for aquaculture industry. Algicidal bacteria , as a way of biological controlling in water environment, is becoming a cause for concern.One high-effect algae-lysing bacteria was isolated and purified from soil in Zhanjiang Caostal Park by the mean of soil plate method. The lytic effects on some harmful algae in spraw pond were studied. And its algae-lytic character,the mean of lytic-algae,the effects of enviromental factors on lytic-algae.The results were as followings:1,According to the studies on the major bacteriological characteristics and 16S rDNA sequence analysis, the strian was Gram positive bacilli, which is motile and have gemma. The sequence analysis of 16S rDNA fragment of strain showed that it shares 99.7% sequence homology with some strain of Bacillus brevis. According that,the strain belongs to Brevibacillus laterosporus.2,The algae-lysing experiment of strian in algae-soil plate and liquid medium showed it can lyse in the two ways. Therefore, this strian have a wider algae–lysing ability.3,According to different proportion of bacterium and algae, the result of co-cultivating as following: the concentration of bacterium have significant effect on chlorophyll-a content of Oscillatoria sp.and Phormidium sp. when the ratio of the suspension of bacterium and algae is 1:10 (the concentration of bacterium is about 105 cfu/mL), the strian have a facilitation on the chlorophyll a content of algae; while the ratio of the suspension of bacterium and algae is 1:2(the concentration of bacterium is about 107 cfu/mL), the strian have inhibition on the chlorophyll a content of algae; while the ratio of the suspension of bacterium and algae is 1:1(the concentration of bacterium is about 109 cfu/mL), the strian have a intensive inhibition.on chlorophyll-a content of algae. Therefore, The threshold density of the strian for significant cell lysis is about 107 cfu/mL.4,By the methods of filtrating,centrifugation,ultrasonication and heating of bacterium culture, they have significant effects on the chlorophyll-a content of Oscillatoria sp. and Phormidium sp(.P<0.05), and the inhibitory effect on chlorophyll-a content of two blue-green algae without untreatment was significantly higher than other grades. Comparing to the control groups,The chlorophyll-a content of the two blue-green algae reduced by74.18%,85.34% separetaly. The lytic substance is nonprotein and have a high thermal stability. Therefore, the strian lysed algae by drect and inderect ways, and secreting lytic substance is the mian algicidal factor.5,The lytic effects on Oscillatoria sp., Phormidium sp., Alexandrium mimutum and Cyclotella striata were tested in the fluid nutrient medium under laboratory conditions. The results showed that algae-lysing bacteria can lyse Phormidium sp. and Alexandrium mimutum obviously, and have very strong inhibitory effect on Oscillatoria sp., but it has no effect on Cyclotella striata..By observation of the cells of algae and the detection of chlorophyll a, In 24 hours, Alexandrium mimutum was easy to congregate and a large amount of cells were ruptured after adding the cultures. After 7 days, compared to the control groups,The chlorophyll-a content of Phormidium sp. reduced by91.45%;and the chlorophyll-a content of Oscillatoria sp. decreased by 75.83%. Therefore, the strian have a algae-lysing selection.6,In different light condition(L:D=14h:10h,0h:24h,24h:0h), the strian have significant effect on the growth of Oscillatoria sp.and Phormidium sp.(P<0.05). Duncan multiple comparison displayed that the inhibitory effect on chlorophyll-a content of two blue-green algae was significantly higher than other grades when the light condition is L:D=0h:24h. So, the strian have powerfully inhibition on the chlorophyll-a content of algae in the dark condition.7,In different temprature condition, the strian have significant effect on the growth of Oscillatoria sp.and Phormidium sp.(P<0.05)Duncan multiple comparison displayed that the inhibitory effect of chlorophyll a of two blue-green algae was significantly higher than other grades when temperature was from 20 to 25℃. So, the optimal temperature of algae-lysing is 20～25℃.8,In different salinity condition, the strian have significant effect on the growth of Oscillatoria sp.and Phormidium sp.(P<0.05). Duncan multiple comparison displayed that the inhibitory effect on chlorophyll-a content of two blue-green algae was significantly higher than other grades when salinity was from 20 to 25. So, the optimal salinity of algae-lysing is 20～25.