Response of neutrophilic Shewanella violacea to acid stress: growth rate, organic acid production, and gene expression
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Neutrophilic Shewanella violacea is isolated from deep-sea sediments and its response to high pressure and high salinity has been investigated. Here, the pure effects of acidic pH on S. violacea physiology were examined, aiming at further understanding of its stress response mechanism. S. violacea could grow at initial pH of 5.0–7.0 without pH adjustment during the test at atmospheric pressure, and the lowest growth rate was obtained at pH 5.0. The pH of the same growth culture with an initial pH of 5.0 rose toward a neutral pH of ~ 7.0 at the exponential growth phase, indicating that S. violacea has a mechanism for acid neutralization. When S. violacea cells were grown at the fixed pH of 5.0, about five times higher concentrations of butyric and isovaleric acids were produced than at pH 7.0. The expression level of the genes encoding three enzymes for isovaleric acid synthesis from l-leucine was also found to be upregulated in S. violacea cells grown at the fixed pH of 5.0 compared with at pH 7.0 through RNA-seq analysis. Therefore, S. violacea at least produces isovaleric acid in its response to acid stress, which further deepens our understanding of the stress response mechanism inherent in this bacterium.
KeywordsAcid neutralization Acid stress Isovaleric acid pH Shewanella violacea
Solid-phase microextraction and gas chromatography coupled with mass spectrometry
This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Nos. 26240045 and 16K07692 to Y.S.), a Grant from the Japan Society for the Promotion of Science (No. 25–1446 to S.F.), and a Grant-in-Aid for Fundamental Research from the Graduate School of Biosphere Science, Hiroshima University to S.F. L.L. was very grateful to the Indonesia Endowment Fund for Education, Ministry of Finance, Republic of Indonesia, for the scholarship.
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Conflict of interest
The authors declare that they have no conflict of interest.
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