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Transcriptomic consequence of the mutation in the response regulator gene gacA of the two-component regulatory system GacS/GacA in the rhizosphere biocontrol strain Pseudomonas aeruginosa M18

ABSTRACT: To investigate the influence of GacA on the genome-wide transcription of the rhizobacterium P. aeruginosa M18, DNA microarray experiments were carried out to compare the transcriptional profile of M18 with that of the gacA mutant grown to the early stationary phase (OD600 = 5.0 ~ 5.5) in KMB media. When compared with the M18 parental strain, the transcriptomic profile of gacA mutant revealed the significantly differential expression (increased or decreased by at least 2-fold as well as p-value < 0.05) of 839 genes, which represent approximately 15% of all 5696 annotated genes in the M18 genome. Of these 839 genes, 472 were downregulated and 367 genes were upregulated by the gacA mutation.

ORGANISM(S): Pseudomonas sp. M18 Pseudomonas aeruginosa M18

PROVIDER: GSE43655 | GEO | 2013/06/07

SECONDARY ACCESSION(S): PRJNA186941

REPOSITORIES: GEO

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Project description:GacS/GacA comprises a two-component regulatory system that controls the expression of secondary metabolites required for the control of plant diseases in many pseudomonads. High mutation frequencies of gacS and gacA have been observed in liquid culture. We examined whether gacS/gacA mutants could competitively displace the wild-type populations on roots and thus pose a threat to the efficacy of biological control. The survival of a gac mutant alone and in competition with the wild type on roots was examined in the biological control strain Pseudomonas aureofaciens 30-84. In this bacterium, GacS/GacA controls the expression of phenazine antibiotics that are inhibitory to plant pathogenic fungi and enhance the competitive survival of the bacterium. Wheat seedlings were inoculated with strain 30-84, and bacteria were recovered from roots after 21 days in sterile or nonsterile soil to check for the presence of gacS or gacA mutants. Although no mutants were detected in the inoculum, gacS/gacA mutants were recovered from 29 out of 31 roots and comprised up to 36% of the total bacterial populations. Southern hybridization analysis of the recovered gacA mutants did not indicate a conserved mutational mechanism. Replacement series analysis on roots utilizing strain 30-84 and a gacA mutant (30-84.gacA) or a gacS mutant (30-84.A2) demonstrated that although the mutant population partially displaced the wild type in sterile soil, it did not do so in natural soil. In fact, in natural soil final rhizosphere populations of wild-type strain 30-84 starting from mixtures were at least 1.5 times larger than would be predicted from their inoculation ratio and generally were greater than or equal to the population of wild type alone despite lower inoculation rates. These results indicate that although gacS/gacA mutants survive in natural rhizosphere populations, they do not displace wild-type populations. Better survival of wild-type populations in mixtures with mutants suggests that mutants arising de novo or introduced within the inoculum may be beneficial for the survival of wild-type populations in the rhizosphere.

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Transcriptomic consequence of the mutation in the response regulator gene gacA of the two-component regulatory system GacS/GacA in the rhizosphere biocontrol strain Pseudomonas aeruginosa M18

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