Isolation and characterization of a lipolytic bacterium capable of growing in a low-water-content oil-water emulsion

Abstract

A unique lipolytic bacterium was isolated in a selective growth system consisting of 99% triglycerides and a 1% water phase. The bacterium, termed Pseudomonas aeruginosa YS-7, was able to grow in an environment of low water content and could also survive amphipathic, osmotic, and matrical water stress in a triglyceride-rich culture. The isolated strain was identified as P. aeruginosa on the basis of standard physiological, biochemical, and serological assays. The strain is a gram-negative motile rod, aerobic, pigment forming, and capable of growing at 42 degrees C. It is highly tolerant of high concentrations of the cationic detergent cetyltrimethylammonium bromide and of the fatty acid salts derived from bacterial hydrolysis of the oil. Growth of the bacterium in a pure culture in a 99% triglyceride medium lasted until most of the water was evaporated or consumed. Growth was accompanied by triglyceride hydrolysis, which continued to occur even after growth saturation until the water was totally depleted. No loss of viability was observed when the culture was maintained under water-depleted conditions for an additional 40 h. A second cycle of bacterial growth and triglyceride hydrolysis was immediately initiated upon the addition of 1% (vol/vol) water to the culture. Lipase activity was stable regardless of changes in culture conditions. The isolated strain is uniquely resistant to severe water stress in a triglyceride-rich medium or under cold acetone precipitation compared with 12 other microbial strains, including bacteria and yeasts. Among these 12, only the lipolytic strains grew in the 99% triglyceride medium, but they reached a cell mass fourfold smaller than that of P. aeruginosa YS-7.(ABSTRACT TRUNCATED AT 250 WORDS)