The role of ClpP, RpoS and CsrA in growth and filament formation of Salmonella enterica serovar Typhimurium at low temperature.

Gitte Maegaard Knudsen,Line Elnif Thomsen,Maj-Britt Nielsen,John Elmerdahl Olsen,Ivan Rychlik,Søren Aabo

doi:10.1186/s12866-014-0208-4

Gitte Maegaard Knudsen, Line Elnif Thomsen + Show 4 more

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https://doi.org/10.1186/s12866-014-0208-4

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Abstract

BackgroundSalmonellae are food-borne pathogens of great health and economic importance. To pose a threat to humans, Salmonellae normally have to cope with a series of stressful conditions in the food chain, including low temperature. In the current study, we evaluated the importance of the Clp proteolytic complex and the carbon starvation protein, CsrA, for the ability of Salmonella Typhimurium to grow at low temperature.ResultsA clpP mutant was severely affected in growth and formed pin point colonies at 10°C. Contrary to this, rpoS and clpP/rpoS mutants were only slightly affected. The clpP mutant formed cold resistant suppressor mutants at a frequency of 2.5 × 10−3 and these were found not to express RpoS. Together these results indicated that the impaired growth of the clpP mutant was caused by high level of RpoS. Evaluation by microscopy of the clpP mutant revealed that it formed filamentous cells when grown at 10°C, and this phenotype too, disappered when rpoS was mutated in parallel indicating a RpoS-dependency. A csrA (sup) mutant was also growth attenuated a low temperature. An rpoS/csrA (sup) double mutant was also growth attenuated, indicating that the phenotype of the csrA mutant was independent from RpoS.ConclusionsThe cold sensitivity of clpP mutant was associated with increased levels of RpoS and probably caused by toxic levels of RpoS. Although a csrA mutant also accumulated high level of RpoS, growth impairment caused by lack of csrA was not related to RpoS levels in a similar way.

Highlights

IntroductionTo pose a threat to humans, Salmonellae normally have to cope with a series of stressful conditions in the food chain, including low temperature
Salmonellae are food-borne pathogens of great health and economic importance
Misfolding of proteins is not a prominent feature of stress caused by temperature down shift [1], Staphylococcus aureus carrying mutations in the clpP and clpX genes are severely affected in formation of colonies at 17°C [8]. clpP is likewise essential for acclimation to growth below optimal temperature in other bacteria such as Streptococcus pneumoniae [9]

Summary

Introduction

To pose a threat to humans, Salmonellae normally have to cope with a series of stressful conditions in the food chain, including low temperature. We evaluated the importance of the Clp proteolytic complex and the carbon starvation protein, CsrA, for the ability of Salmonella Typhimurium to grow at low temperature. Degradation of abnormal proteins is dependent on proteases such as Lon and the Clp proteolytic complex [6]. The latter consists of the ClpP protease subunits where degradation takes place coupled with ClpX or ClpA ATPase/chaperone subunits responsible for substrate recognition, unfolding of proteins and translocation into the ClpP protease (reviewed by Gottesman [7]). Misfolding of proteins is not a prominent feature of stress caused by temperature down shift [1], Staphylococcus aureus carrying mutations in the clpP and clpX genes are severely affected in formation of colonies at 17°C [8]. clpP is likewise essential for acclimation to growth below optimal temperature in other bacteria such as Streptococcus pneumoniae [9]

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