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Growth-phase specific regulation of cviI/R based quorum sensing associated virulence factors in Chromobacterium violaceum by linalool, a monoterpenoid

Abstract

Quorum sensing (QS)-dependent gene regulation in bacteria performs a vital role in synchronization of cell-density-dependent functions. In Chromobacterium violaceum QS-dependent cviI/R regulatory genes are activated during the mid- or late-exponential phase of growth. However, sufficient evidence is lacking on the role of QS inhibitors on gene regulation at different phases of growth. Hence, we report the role of linalool, a natural monoterpenoid on QS mediated gene regulation at different stages of growth in C. violaceum by performing biosensor, growth kinetic and gene expression studies. In vitro and in vivo studies were performed for establishing role of linalool in reducing the virulence and infection by using HEK-293 T cell lines and Caenorhabditis elegans models respectively. C. violaceum CV026 with C6-HSL was used as control. The results showed linalool to be a QS inhibitor with an estimated IC50 of 63 µg/mL for violacein inhibition. At this concentration the cell density difference (delta OD600) of 0.14 from the compound was observed indicating the quorum concentration. The expression of cviI/R was initiated at mid-log phase (~ 18 h) and reached the maximum at 36 h in control whereas in treatment it remained significantly downregulated at all time points. The expression of violacein biosynthetic genes vioA, vioC, vioD and vioE was also downregulated by linalool. Infection studies with linalool showed higher survival rates in HEK-293T cell lines and C. elegans compared to the infection control. Taken together, this study proves linalool to be a QS inhibitor capable of attenuation of QS by controlling the cell density through cviI/R downregulation at the early phase of growth and hence offering scope for its application for controlling infections.

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All relevant data are within the paper and its Supporting Information files.

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Acknowledgements

The authors thank Ms. Fida Fathima for the technical support provided during in vitro infection studies and Mr. Sukesh Kumar for helping in the execution of the C. elegans infection studies.

Funding

The first author Ms. Kanekar Saptami is recipient of Indian Council of Medical Research-Senior Research Fellowship (Reg ID: 2019-5152/CMB/BMS).

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KS designed and executed all the experiments, analysed the results, and prepared the manuscript. RPD framed the study, designed all experiments, analysed the data, and prepared the manuscript. Both the authors approved the manuscript for submission.

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Correspondence to Rekha Punchappady Devasya.

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Kanekar, S., Devasya, R.P. Growth-phase specific regulation of cviI/R based quorum sensing associated virulence factors in Chromobacterium violaceum by linalool, a monoterpenoid. World J Microbiol Biotechnol 38, 23 (2022). https://doi.org/10.1007/s11274-021-03208-x

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  • DOI: https://doi.org/10.1007/s11274-021-03208-x

Keywords

  • Quorum sensing
  • cviI/R regulation
  • Linalool
  • C. violaceum
  • In vivo infection