The Application Of Bdellovibrio-and-like-organisms(BALOS) In The Culture Of Isochrysis Galbana

Isochrysis galbana, a species of marine microalgae, contains extremely rich nutrients,such as protein, unsaturated fatty acids, carbohydrates and Vitamins, and is of substantialpotential in aquaculture for its good nutritive characteristics, especially to mollusks larvae,fish and crustaceans in the early stages of growth. However, due to their moderate growthconditions which require no extremes of temperature, salinity and pH, they are easily to becontaminated with bacteria during the culture, separation and purification process. This mayresult in the aging of algae sooner and affects algal growth, or even cause diseases. As a result,to find a safe and efficient way to control the bacteria is necessary. It means a lot to thelarge-scale cultivation of Isochrysis galbana as well as to the healthy development ofaquaculture.Bdellovibrio-and-like-organisms （BALOS） are predators of other bacteria and havebroad application prospects in the control of bacteria. In this thesis, the optimal medium andculture conditions of Isochrysis galbana were studied in the intelligent light incubator firstly.On this basis, we cultured the algae in the vats indoor and conducted the follow-upexperiments. Different concentrations of Bdellovibrio （BD-DLL） were added in the algaeregularly, and the number of the total heterotrophic bacteria and the Vibrio were enumeratedevery24hours to analyze the effect of Bdellovibrio on the bacteria control. At the same time,the growth index of the algae and the water quality indicators were determined to study theeffect of Bdellovibrio on the algae growth.The optimal medium obtained is: NaNO₃,30mg/L; CO（NH₂）₂,30mg/L; NaHCO₃,400mg/L, KH₂PO₄,8mg/L; FeC₆H₅O₇,0.5mg/L; VB₁,200ug/L; VB₁₂,1.0ug/L, in1L ofseawater.The results showed that Bdellovibrio （BD-DLL） can effectively control the population ofthe total heterotrophic bacteria and the Vibrio both in the water and on the surface of the algaein the first24hours （p<0.05）. The effect of the low-dose group （10³pfu/ml） was better, whichcan reduce the total bacteria number and the Vibrio number by3-4lg at48hours after theaddition of BD-DLL. During the experiment, the population of BD-DLL increased rapidly within the first24hours after addition, and then decreased gradually after reaching themaximum. The bacterial control effect of BD-DLL on the number of the total heterotrophicbacteria and the Vibrio began decreasing72hours after the addition. As for the effect ofBD-DLL on the growth of the algae, the results showed that in comparation to the control,algae in the experimental group experienced a shorter lag phase. However, Bdellovibrio（BD-DLL） had no significant effect on the growth of the algae （p<0.05）. Besides, compared tothe control, algae in the experimental group had a relatively longer stable phase, with theeffect more obvious in the low-dose group （10³pfu/ml）. Bdellovibrio （BD-DLL） also hadsome influence on the biomass of the algae. Compared to the control, the highest density ofthe alagl cells in the low-dose group （10³pfu/ml） was significant higher （p<0.05）, whichexceeded the control by7.8%. Besides, the yield of the algae in the low-dose group wassignificantly higher than that in the control （p<0.05）, with the number being0.855±0.010g/Land0.552±0.021g/L respectively. The results also showed that Bdellovibrio （BD-DLL） hadno effect on the total fat content of the algae as well as on the pH in the water （p>0.05）. At thelate growth stage of the algae, dissolved oxygen in the experimental group was slightly higherthan that in the control, however, the differences were not obvious at the earlier stage.