Consejo Superior de Investigaciones Cient´ıficas, Environmental Protection Department, Estacio´ n Experimental del Zaid´ın, Granada, Spain.
FEMS Microbiol Lett. 2011 Aug;321(2):107-14. doi: 10.1111/j.1574-6968.2011.02317.x. Epub 2011 Jun 15.
In Pseudomonas putida, as in many other eubacteria, cyclopropane fatty acids (CFAs) accumulate in the membrane during the stationary phase of growth. Here, we show that cfaB gene expression in P. putida KT2440 is dependent on the RpoS sigma factor that recognizes the sequence 5'-CTACTCT-3' between -8 and -14. We have carried out a mutational study of the cfa promoter and have determined that positions -9, -12, -13 and -14 are the most critical for maximal activity. In P. putida, the substrates of the CFA synthase, cis-unsaturated fatty acids (cis-UFAs), are also substrates for another stress-related enzyme, the cis-trans isomerase (CTI). Despite using the same substrates, we have found that the activity of the CTI is not limited by the CFA synthase activity and vice versa. For instance, in a cfaB knockout mutant, the amount of trans-UFAs synthesized after a specific stress was no higher than in the parental background despite the fact that there are more cis-UFAs available to be used by the CTI as substrates. In this regard, in a cti-deficient mutant background, the levels of CFAs were similar to those in the parental one under the same conditions.
在恶臭假单胞菌中，与许多其他真细菌一样，环丙烷脂肪酸 (CFA) 在生长的静止期积累在膜中。在这里，我们表明恶臭假单胞菌 KT2440 中的 cfaB 基因表达依赖于识别 -8 到 -14 之间的序列 5'-CTACTCT-3' 的 RpoS 西格玛因子。我们已经对 cfa 启动子进行了突变研究，并确定位置 -9、-12、-13 和 -14 对于最大活性最为关键。在恶臭假单胞菌中，CFA 合酶的底物，顺式不饱和脂肪酸（cis-UFA），也是另一种与应激相关的酶，即顺反异构酶（CTI）的底物。尽管使用相同的底物，但我们发现 CTI 的活性不受 CFA 合酶活性的限制，反之亦然。例如，在 cfaB 敲除突变体中，在特定应激后合成的反式 UFA 的量并不高于亲本背景，尽管有更多的 cis-UFA 可被 CTI 用作底物。在这方面，在 cti 缺陷突变体背景下，CFAs 的水平在相同条件下与亲本相似。
