Effect Of Bacteria On The Growth And Biochemical Components Of Heterotrophic Chlorella Protothecoides

In this study the effect of bacteria on the growth and lipid; carbohydrate; protein content of heterotrophic Chlorella protothecoides was investigated and effective aintibiotics were screened. First; the unpurified chlorella was cultivated both through shaken flask culture and aeration culture; and the aeration culture was found to bring more bacteria contamination to the medium. During the heterotrophic cultivation; C. protothecoides represented lipid accumulation and consumption of carbohydrate and protein. The final cell number in aeration culture was 25×10~6/ml; which was lower than that in shaken flask culture (28×10~6/ml). The lipid content at 168h was 0.21g/g (dry weight) in aeration culture; which was lower than the value of 0.24g/g in shaken flask culture. However; the carbohydrate contents were similar and the protein contents under aeration and shaken flask culture were 0.33g/g and 0.31g/g; respectively. This indicated that contaminated bacteria in aeration culture could inhibite the growth and lipid accumulation of heterotrophic C. protothecoides. DGGE was applied to analyse the bacteria diversity in aeration culture, which demonstrated the occurrence of bacteria contamination. Meanwhile, the bacteria were isolated. The analysis of DGGE bands and the identification of isolated bacteria showed that the alga associated bacteria and the contaminated bacteria all belong to Bacillus sp.. Then the pure culture of C. protothecoides was obtained. After purification, the cell density of alga achieved 30×10~6/ml, which was 1.1-fold that of the unpurified. The lipid content at 168h was 0.30g/g, 1.25-fold of the unpurified. There was no considerable change in carbohydrate content and the protein content reduced by 20%. After the purified alga was cultivated in aeration culture, its growth was inhibited and the lipid content was only 86% that of the pure culture. These results indicated the importance of contamination control for the growth and lipid accumulation of heterotrophic C. protothecoides. Then antibiotics were used to prevent bacteria contamination. The effects of different antibiotics on C. protothecoides were studied. 10μg/ml,25μg/ml Ampicillin and 10,25,50,100μg/ml Chloramphenicol were found having no negative effects on the growth and lipid accumulation of C. protothecoides. Adding 25μg/ml Chloramphenicol was proved to be an effective way to control bacteria contamination. With contamination controlled, the cell density in aeration culture increased to 33×10~6/ml, 16% higher than the value in contaminated culture. And the lipid content reached as high as 0.40g/g, which was 1.6-fold that of the contaminated culture.