假单胞菌株M18gacA基因对BHL和HHL合成正调控及对PCA合成负调控无相关性

经初步鉴定,假单胞菌株(Pseudomonassp.)M18至少能产生5种N-酰基高丝氨酸内酯类(N-acyl-homoserinelactones,AHLs)信号分子,它们是:N-丁酰高丝氨酸内酯(N-butyryl-L-homoserine lactone,C4-HSL,BHL)、N-己酰高丝氨酸内酯(N-hexanoyl-L-homoserine lactone,C6-HSL,HHL)、N-3-氧-己酰高丝氨酸内酯[N-(3-oxohexanoyl)-L-homoserinelactone,3-Oxo-C6-HSL,OHHL]、N-3-氧-辛酰高丝氨酸内酯[N-(3-oxooctanoyl)-L-homoserine lactone,3-Oxo-C8-HSL,OOHL]和N-3-氧-癸酰高丝氨酸内酯[N-(3-oxodecanoyl)-L-homoserine lactone,3-Oxo-C10-HSL,ODHL)。在gacA突变菌株M18G中,信号分子的积累量明显减少,且只能检测出其中的4种;同时,吩嗪-1-羧酸(Phenazine-1-carboxylic acid,PCA)的合成量比野生株M18提高了2倍左右。在M18菌株中,基因rhlⅠ的编码产物参与BHL和HHL的合成。构建rhlI’-’lacZ翻译融合表达质粒pMEIZ,分别导入野生株M18和突变株M18G,突变株M18G的半乳糖苷酶活性比野生株M18下降约40%,表明GacA对基因rhlI的表达具有正调控作用。但是,在野生株M18和突变株M18G的发酵液中,分别或同时添加过量的外源BHL和HHL,对PCA合成的影响不显著,表明在突变株M18G中,PCA合成量的增加与BHL和HHL合成量的减少没有明显的相关性。

Negative regulation on PCA production is not correlated with positive regulation on BHL and HHL synthesis by gacA in Pseudomonas sp. M18

At least 5 kinds of N-acyl-homoserine lactones(AHLs) were identified in Pseudomonas sp.M18.They were: N-butyryl-L-homoserine lactone(C4-HSL,BHL),N-hexanoyl-L-homoserine lactone(C6-HSL,HHL),N-(3-oxohexanoyl)-L-homoserine lactone(3-Oxo-C6-HSL,OHHL),N-(3-oxooctanoyl)-L-homoserine lactone(3-Oxo-C8HSL,OOHL) and N-(3-oxodecanoyl)-L-homoserine lactone(3-Oxo-C10-HSL,ODHL).Compared with the wide-type strain M18,the variety of the AHLs in the gacA mutant strain M18G reduced to 4 species with the decreased quantity.But the phenazine-1-carboxylic acid(PCA) production was increased by about 2-fold.The product of rhlI plays an important role in synthesizing BHL and HHL.The rhlI'-'lacZ translational fusion expression plasmid pMEIZ was constructed in vector pME6015 and then was introduced into the wild-type strain M18 and the gacA mutant strain M18G.The galactosidase activity in chromosomal gacA disruption mutant was only 60% of that in the wild-type strain M18.This result suggested that GacA could regulate the rhlI expression positively.There was no influence on PCA production by adding exogenous BHL and HHL and both together to the culture of strains M18 and M18G.This result suggested that there was no relation between GacA's negative regulation on PCA production and positive regulation on BHL and HHL synthesis.