Abstract: To reduce the cost of fermentation and improve the efficiency of microbial oil recovery, we carried out an open fermentation exploration of oil-producing functional bacterium SQ6 (rhamnolipids-producing strain). We investigated the growth at different temperatures, rhamnolipid production, surface tension, emulsification index and other parameters of strain SQ6 under two fermentation modes, i.e., conventional fermentation and open fermentation. The homologous composition of rhamnolipid products was analyzed by liquid chromatography-high resolution mass spectrometry, and the bacterial community structure and percentage of microbial contaminants of open fermentation were analyzed by highthroughput sequencing. The results showed that the highest growth of strain SQ6 was at 45 ℃, and the highest temperature for synthesizing a large amount of rhamnolipids was 40 ℃. The fermentation temperature with the highest yield and lowest miscellaneous bacteria rate in open fermentation was 37 ℃, the yield of rhamnolipids reached 7050.1 mg·L^-1, which was only 33% lower than that of conventional fermentation (10513.2 mg·L^-1), and miscellaneous bacteria rate was the lowest reaching 3.13%. For the SQ6 strain, high-temperature fermentation did not have a stronger inhibitory effect on microbial contaminants and reduced the production of rhamnolipids. The structure of fermentation product showed that the main product was mono-rhamnolipids, accounting for 96.1%. The synthesis of mono-rhamnolipids in high concentration may be the main reason for the stronger inhibition rate of bacterial contaminants in open fermentation under medium temperature. Therefore, strain SQ6 is a functional oil recovery bacterium with substantial open fermentation potential.

Key words: Pseudomonas aeruginosa, open fermentation, rhamnolipids, inhibition rate of miscellaneous bacteria