Characteristic Of An Algae-lytic Bacterium And The Optimization Of Its Fermentation

The cyanobacteria can proliferate rapidly to water blooms and scums under favorable conditions in eutrophic fresh, brackish and marine waters throughout the world. Microcystis may potentially produce toxins microcystins that is considerated as the most common hepatotoxins. It has been proved that microcystins can cause liver damage as well as tumour carcinogen. These toxins have caused illness and death of not only animals but also humans. Biological control by natural algae-lytic micro-organisms is a potential measure against algae blooms. In our test, strain 9404 isolated from Russian soil was studied.Traditional phenotype classification, chemotaxonology and other ordinary bacteria taxonology were used to study strain 9404 from Russian soil. Its morphological, cultural physiological, biochemical characteristics andchemotaxonomy were studied. The strain is bacilliform. And its cell diameter is less than 1μm. It is Gram positive, it can form spore. So it is specie of Bacillus. And the spore formed by this antagonistic bacterium can make the sporangium swollen. It can grow without oxygen. Further more, the antagonistic bacterium can not hydrolyze starch. It can ferment glucose, but can not produce gas. And its H₂O₂ reaction is negative, it can not grow in broth medium. So it was identified as Bacillus larvae.In the anti-cyanobacteria test, the powder, the culture and the supernatant of the B. larvae were studied lytic effects on the lytic-effect on Microcystis aeruginosa 905, Microcystis aeruginosa 562 and Nostoc. The results showed that the B. larvae have distinctively algae-lytic effect. Compared to the control, the treatment looked on brown by naked eye; there are many fragments and little intact cells of Micrcystis aeruginosa 905 by light microscope; scanning by electron microscope, cells' wall was broken, and cytoplasm flowed out of cells, and cells broken down. The activity of the inhibitive substance was not influenced when at 60℃10min. Results indicated that the algae-lytic substance is stable against heat and is not stable against Proteinase K in certain extend. It is inferred to be protein or compound which contrains protein.The effects of a number of factors on the production of strain B. larvae against Microcystis aeruginosa 905 were studied, including pH, temperature and cultivating time, carbon source and nitrogen source. The optimization pH 7.0-7.5, cultural temperature 37℃, and B. larvae was cultivated for 96 h at 170 r/min. On the basis of these, the recipe of fermentation medium was optimized through uniform-design. A suitable fermentation condition was found for algae-lytic production of B. larvae. The optimal conditions were as follows: corn flour 5 g/L, ammonium soleplate 3 g/L, NaCl 0.2 g/L.