Aims(i) To obtain and identify the predatory bacteria for the control of contaminated bacteria and to promote the autotrophic growth of Chlorella USTB-01. (ii) To identify and measure the different cell numbers in microalgal culture using flow cytometer. Methods and ResultsA predatory bacterial strain was isolated using Escherichia coli BL21 as a sole prey host, which was identified as Bdellovibrio USTB-06 by the analysis of 16S rDNA sequence. A flow cytometer was successfully used to identify and measure the cell numbers of Chlorella USTB-01, the contaminated bacteria and Bdellovibrio USTB-06 simultaneously in the autotrophic culture of Chlorella USTB-01 according to the identification of the different cell sizes. With the addition of Bdellovibrio USTB-06 at initial 10(4) plaque-forming units per ml, the contaminated bacteria severely decreased by about five counts (in log(10)CFU per ml) and the growth of Chlorella USTB-01 was greatly increased by 370% compared with those of control respectively. ConclusionsBdellovibrio USTB-06 could effectively promote the growth of Chlorella USTB-01 via the killing of the contaminated bacteria. Significance and Impact of the StudyOur study reveals a good biotechnology method to increase the growth of Chlorella USTB-01 which is very important in the industry of microalgal culture.