温度对假单胞rsmA突变株M-18R合成Plt和PCA的区别性影响

次生代谢物阻遏蛋白(Repressor of secondary metabolite,Rsm)A是一种全局性调控因子,与mRNA的RBS结合,转录后水平上抑制基因翻译。运用同源重组技术,构建了假单胞茵(Pseudomonas sp．)M-18的rsmA突变菌株M-18R。在37℃、28℃恒温和短期升温(37℃、4h培养,转28℃继续培养)条件下,比较野生株M-18和突变株M-18R生物合成藤黄绿菌素(Plt)和吩嗪-1-羧酸(PCA)的量。在37℃条件下,M-18和M-18R合成这两种抗生物质的能力几乎受到完全抑制。在28℃条件下,M-18R合成P11的量约为野生型M-18的10倍,达到270μg／mL,但是合成PCA的量仅为野生型的50％。经短期升温培养,M-18的Plt合成量明显下降,PCA产量降低不显;相反,M-18R合成Plt的量达到400μg／mL,但PCA产量的变化仍不明显。推测,M-18菌株细胞内存在着某种与RsmA相关联的温度敏感因子,在RsmA缺失条件下,作为专一性激活剂促进Plt的生物合成,但是,并不参与对PCA合成的调控。

Differential Effect of Temperature on Plt and PCA Synthesis in A rsmA Inactivated Mutant Strain of Pseudomonas sp. M-18

Rsm (repressor of secondary metabolite) A is an mRNA binding protein which functions as a global repressor to control multiple genes at the posttranscriptional level. Using homologous recombination technique a chromosomal rsmA inactivated mutant strain M-18R was constructed in Pseudomonas sp. M-18, a strain of plant-growth-promoting rhizobacteria, which could inhibit several soilborn phytopathogens by producing secondary metabolites including phenazine-1-carboxylic acid (PCA) and pyoluteorin (Plt) in one single strain. To further study the effect of RsmA on the synthesis of Plt and PCA in the wild type strain M-18, the dynamic curves of Plt and PCA produced respectively by M-18 and M-18R were measured in KMB medium under different temperature conditions such as 37 degrees C constant, 28 degrees C constant and nonconstant (37 degrees C 4 hours at first and then 28 degrees C constant) cultivation. The synthesis of both Plt and PCA were almost inhibited in the cultures under the condition of 37 degrees C. At 28 degrees C, however, compared with the wild type strain M-18, the mutant strain produced tenfold amount of Plt, while the production of PCA decreased only about 50%. When cultivated under the nonconstant condition, the amount of Plt produced by M-18R could reach 400 microg/mL while the PCA production was not significantly affected, but in the wild type strain M-18, the amount of Plt production decreased obviously while the PCA production was not affected in comparison with the results at 28 degrees C constant. These results suggest that a temperature sensitive factor exists to function as an activator independent of RsmA to promote the synthesis of Plt in the rsmA mutant strain M-18R while it may bind with RsmA to repress the synthesis of Plt in the wild type strain M-18. But this factor did not exert any affect on the synthesis of PCA.