Growth Temperature-Dependent Conversion of De novo -Synthesized Unsaturated Fatty Acids into Polyhydroxyalkanoic Acid and Membrane Cyclopropane Fatty Acids in the Psychrotrophic Bacterium Pseudomonas fluorescens BM07

摘要

A psychrotrophic bacterial strain, Pseudomonas fluorescens BM07, synthesized unsaturated fatty acids (UFA) from fructose in response to lowering of growth temperature, and incorporated them into both polyhydroxyalkanoic acid (PHA) and membrane lipid. The blocking of PHA synthesis by adding 5 mM 2-bromooctanoic acid to the growth medium, containing 70 mM fructose, was found to be a useful means to profile the composition of membrane lipid by gas chromatography. As the growth temperature changed from 35 to 5℃, the total content of two UFA, 3-hydroxy-cis-5-dodecenoic acid (C_(12:1)) and 3-hydroxy-cis-7-tetradecenoic acid (C_(14:1)), in PHA increased from 31 to 44 mol%. The growth at lower temperatures also led to an increase in the level of two major UFA, palmitoleic acid (C16:1 cis9) and cis-vaccenic acid (C18:1 cis11), in membrane lipid. A fraction of these membrane-lipid UFA was converted to their corresponding cyclopropane fatty acids (CFA). The CFA conversion was a function of culture time, exhibiting biphasic increase before and after entering the stationary phase. However, pH changes in growth media had no effect on the CFA conversion, which is contrary to the case of E. coli reported. The cells grown at 30℃ responded to a cold shock (lowering the medium temperature down to 10℃) by increasing the level of C16:1 cis9 and C18:1 cis11 up to that of 10℃-grown control cells and concomitantly decreasing the relative level of cis-9,10-methylenehexadecanoic acid (the CFA converted from C16:1 cis9) from 14 to 8 mol%, whereas the 10-grown cells exhibited little change in the lipid composition when exposed to a warmer environment of 30℃ for 12 h. Based on this one- way response, we suggest that this psychrotrophic strain responds more efficiently and sensitively to a cold shock than to a hot shock. It is also suggested that BM07 strain is a good producer of two unsaturated 3-hydroxyacids, C_(12:1) and C_(14:1).