Restraining Effect Of Six Different Bacteria On Red Tide Alga Scrippsiella Trochoidea

The phenomenon that bacteria restrain alga growth is initially discovered in the nature. The relationship between alga and bacteria is complex. On the one side, metabolic substance of algae is utilized by bacteria living around algae. On the other side, saccharine, protein and the like that are excreted by bacteria can always be used by algae. So, their relationship should be mutual benefit. However, there is a relationship between algae and bacteria that is not mutual benefit. Many studies have shown that bacteria can excrete some extracellular substances that can restrain growth of algae, or even kill algae. Red tide has produced great damage to ocean fish culture as our environment become worse and worse. From the phenomena that growth of algae is restrained by bacteria we have an idea that human may utilize this phenomenato deal with the red tide problem and to control bloom of harmful algae.In this paper, we used red tide alga Scrippsiella trochoidea as experimental material to evaluate the restraining effects of six different bacteria on Scrippsiella trochoidea. The selected six bacteria included Pseudomonas aeruginosa, Pseudomonas putida, Bacillus subtilis, Bacillus megaterium and two kind of Vibrio. All six bacteria can survive in the salt water. The alga and the bacteria were cultured together or singly, and growth parameters of the alga such as cell density, cellulose enzyme activity and lipase activity were measured at different concentrations of bacteria from 9.2 102 to 1.2 108 cfu/ml. The results of this study indicated that all six bacteria had a significant restraining effect on growth of the alga and consequently killed the alga, and the mechanism that the bacteria killed the alga may be that the bacteria foraged the alga cell. Our data from the bacteria culture liquid without enzyme activity by heating in comparison with control showed that the enzyme in the bacteria culture liquid may be the main factor in restraining the growth of algae. There were marked decreases in the algae cell density and cellulose enzyme activity when Scrippsiella trochoidea was cultured with the bacteria than the alga was cultured alone. When comparing the co-culture of the alga and the bacteria with the pure culture of the six bacteria, we found an increase of cellulose enzyme activity only when Scrippsiella trochoidea was cultured with the bacteria Pseudomonas putida andBacillus megaterium but there was a consistently decrease of cellulose enzyme activity when Scrippsiella trochoidea was cultured with the other four bacteria. Of the six bacteria, although V-2 had the highest cellulose enzyme activity when it was cultured singly, its cellulose enzyme activity decreased by 50% when it was cultured with the alga. Furthermore, among the six bacteria examined, only Bacillus subtilis and Bacillus megaterium released lipase, and in particular the lipase activity of Bacillus megaterium was increased by 1.78 times when Bacillus megaterium was cultured with the alga. Likewise, we found that the lipase activity of Bacillus subtilis increased when it was cultured with the algae compared to the bacterium's pure culture liquid.