AUTHOR=Lu Shao-Yeh , Zhao Zhe , Avillan Johannetsy J. , Liu Jinxin , Call Douglas R. 

TITLE=Autoinducer-2 Quorum Sensing Contributes to Regulation of Microcin PDI in Escherichia coli

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02570

DOI=10.3389/fmicb.2017.02570

ISSN=1664-302X

ABSTRACT=<p>The <italic>Escherichia coli</italic> quorum sensing (QS) signal molecule, autoinducer-2 (AI-2), reaches its maximum concentration during mid-to-late growth phase after which it quickly degrades during stationary phase. This pattern of AI-2 concentration coincides with the up- then down-regulation of a recently described microcin PDI (mccPDI) effector protein (McpM). To determine if there is a functional relationship between these systems, a prototypical mccPDI-expressing strain of <italic>E. coli</italic> 25 was used to generate Δ<italic>luxS</italic>, Δ<italic>lsrACDBFG</italic> (Δ<italic>lsr</italic>), and Δ<italic>lsrR</italic> mutant strains that are deficient in AI-2 production, transportation, and AI-2 transport regulation, respectively. Trans-complementation, RT-qPCR, and western blot assays were used to detect changes of microcin expression and synthesis under co-culture and monoculture conditions. Compared to the wild-type strain, the AI-2-deficient strain (Δ<italic>luxS</italic>) and -uptake negative strain (Δ<italic>lsr</italic>) were &gt;1,000-fold less inhibitory to susceptible bacteria (<italic>P</italic> &lt; 0.05). With <italic>in trans</italic> complementation of <italic>luxS</italic>, the AI-2 deficient mutant reduced the susceptible <italic>E. coli</italic> population by 4-log, which was within 1-log of the wild-type phenotype. RT-qPCR and western blot results for the AI-2 deficient <italic>E. coli</italic> 25 showed a 5-fold reduction in <italic>mcpM</italic> transcription with an average 2-h delay in McpM synthesis. Furthermore, overexpression of sRNA <italic>micC</italic> and <italic>micF</italic> (both involved in porin protein regulation) was correlated with <italic>mcpM</italic> regulation, consistent with a possible link between QS and <italic>mcpM</italic> regulation. This is the direct first evidence that microcin regulation can be linked to quorum sensing in a Gram-negative bacterium.</p>