茄科雷尔氏菌脂酰CoA脱饱和酶和环丙烷脂肪酸合成酶的鉴定

茄科雷尔氏菌(Ralstonia solanacearum)是一种危害严重的土传植物致病菌,其宿主范围广泛,在世界各地严重影响重要经济作物的生产.研究茄科雷尔氏菌的生理特性,探索其致病机理,有利于研发防治青枯病的技术与方法.脂肪酸是细菌细胞重要的组成物质,但是茄科雷尔氏菌脂肪酸合成的机制尚不清晰.本文以茄科雷尔氏菌GMI1000为材料,鉴定了该菌的脂酰Co A脱饱和酶和环丙烷脂肪酸合成酶,并分析了这两种酶在不饱和脂肪酸和环丙烷脂肪酸合成中的作用.结果显示,茄科雷尔氏菌RSc2450编码脂酰Co A脱饱和酶,参与其不饱和脂肪酸合成,但是该菌还存在其他不饱和脂肪酸合成途径.同时发现在茄科雷尔氏菌编码两个可能的环丙烷脂肪酸合成酶蛋白质中,仅有Cfa1(RSc0776)参与了该菌环丙烷脂肪酸的合成,并在低p H和高渗透压的耐受中起作用.该研究结果为深入研究茄科雷尔氏菌脂肪酸合成代谢特点及致病机理奠定了基础.

Identification of acyl-CoA Desaturase and Cyclopropane Fatty Acid Synthase in Ralstonia solanacearum

Ralstonia solanacearum, a soil-borne destructive plant pathogen, has an unusually wide host range, and causes a bacterial wilt that seriously affects the production of many economically important crops in the world. Thus, investigation of physiological metabolism in R. solanacearum will be helpful to develop new ways to control the bacterial wilt. Fatty acids are compulsory components of bacteria. However, the fatty acid biosynthestic mechanism is still unclear in R. solanacearum. In this paper, we identified acyl-CoA desaturase and cyclopropane fatty acid synthase of R. solanacearum GMI1000, and characterized their functions in biosynthesis of unsaturated fatty acid or cyclopropane fatty acid. First, R. solanacearum RSc2450 (desA) complemented Shewanella oneidensis desA fabA mutant growth on LB without supplemented oleic acid and caused E. coli fabA mutant to produce unsaturated fatty acid. Furthermore, deletion of desA caused R. solanacearum grows weak on BG plate and reduces the palmitoleic acid production. The results showed though R. solanacearum RSc2450 encodes an acyl-CoA desaturase and involves in unsaturated fatty acid biosynthesis, R. solanacearum might possess a novel unsaturated fatty acid biosynthetic pathway. Next, of the two putative cyclopropane fatty acid synthases encoded genes in R. solanacearum, only cfa1 (RSc0776) restored E. coli cfa mutant YYC1257 growth in low pH medium and to produce cis-9, 10-methylene palmitic acid. And deletion cfa1 mutant was sensitive to low pH and high osmotic pressure, and lost the ability to produce cis-9, 10-methylene palmitic acid. These indicated that cfa1 involves in cyclopropane fatty acid synthesis in R. solanacearum and plays roles in adaption to low pH and high osmotic pressure. Moreover, Cfa2 (RSp1446) does not have cyclopropane fatty acid synthase activity, and its function needs further study.