Induction ofrpoSinSalmonella typhimuriumby nutrient‐poor and depleted media is slower than that achieved by a competitive microflora

Abstract

The presence of a viable competitive microflora, at greater than 108 cfu ml−1, is known to advance the induction of RpoS‐mediated gene expression in a sub‐population of Salmonella typhimurium. As starvation is known to induce RpoS, one action of the competitive microflora could be to cause depletion of essential nutrients. The aim of the current experiments was to determine whether this was the case by examining RpoS induction in Salm. typhimurium in reduced nutrient media. RpoS‐mediated gene expression in Salm. typhimurium was not advanced so significantly in ‘conditioned’ or diluted medium as it was in the presence of competitors, which indicates that nutrient depletion was not the responsible mechanism. The effect of a competitive microflora has implications for models of bacterial survival during food processing, as RpoS ultimately regulates both stress resistance and virulence.

Oxidation-reduction potential regulates RpoS levels in Salmonella Typhimurium

“…During growth, 100 μ l samples were taken at intervals for bioluminescence monitoring using a Luminoscan luminometer (Lab‐systems Ltd, Basingstoke, Hants, UK) in which bioluminescence was integrated over a 10‐s counting period. Growth and bioluminescence data were used to calculate the induction time for RpoS‐mediated gene expression in Salmonella , in the same way as described in the work of Aldsworth et al. (1998a,b, 1999) and Dodd and Aldsworth (2002).…”

“…The spvRA:luxCDABE gene fusion is a direct measure of in vivo RpoS availability first constructed by Swift and Stewart (1994). Since then, it has been used in a number of studies to examine RpoS expression under various conditions (Aldsworth et al. 1998a,b, 1999; Thompson et al.…”

Vibrio vulnificus RtxA1 Toxin Expression Upon Contact With Host Cells Is RpoS-Dependent

“…The expressions of some virulence factors are tightly connected by RpoS to general cellular stress responses (Dulebohn et al, 2017 ). RpoS is activated by different environmental stresses, such as nutrient starvation (Aldsworth et al, 1999 ), heat, acid or alkaline treatment (Bhagwat et al, 2006 ), oxidative stress (Gawande and Griffiths, 2005 ), ultraviolet irradiation, and osmotic stress (Berney et al, 2006 ). Under conditions of nutrient deprivation, or as cells enter the stationary phase, Escherichia coli and related bacteria increase the accumulation of RpoS (Battesti et al, 2011 ).…”