Role ofctcfromListeria monocytogenesin Osmotolerance

Abstract

Listeria monocytogenes is a food-borne pathogen with the ability to grow under conditions of high osmolarity. In a previous study, we reported the identification of 12 proteins showing high induction after salt stress. One of these proteins is highly similar to the general stress protein Ctc of Bacillus subtilis. In this study, induction of Ctc after salt stress was confirmed at the transcriptional level by using RNA slot blot experiments. To explore the role of the ctc gene product in resistance to stresses, we constructed a ctc insertional mutant. No difference in growth was observed between the wild-type strain LO28 and the ctc mutant either in rich medium after osmotic or heat stress or in minimal medium after heat stress. However, in minimal medium after osmotic stress, the growth rate of the mutant was increased by a factor of 2. Moreover, electron microscopy analysis showed impaired morphology of the mutant grown under osmotic stress conditions in minimal medium. Addition of the osmoprotectant glycine betaine to the medium completely abolished the osmotic sensitivity phenotype of the ctc mutant. Altogether, these results suggest that the Ctc protein of L. monocytogenes is involved in osmotic stress tolerance in the absence of any osmoprotectant in the medium.Listeria monocytogenes is a food-borne pathogen widely distributed in the environment. This microorganism is of particular concern in the food industry because of its ability to survive and frequently to grow under a wide range of adverse conditions used to preserve food such as low temperature, low pH, and high osmolarity (8). Growth of L. monocytogenes has been reported at NaCl concentrations as high as 10% (21).Most bacteria cope with elevated osmolarity in the environment by intracellular accumulation of compatible solutes, called osmolytes (32). Among the compatible solutes efficient in L. monocytogenes, two quaternary amines, glycine betaine and carnitine, are the most effective (5, 34). The accumulation of these osmoprotectants in L. monocytogenes occurs through osmotic activation of their transport from the medium rather than through de novo synthesis. Accumulation of glycine betaine and carnitine occurs via at least two glycine betaine transporters encoded by the betL gene and the gbu operon (18, 30) and one carnitine transporter encoded by the opuC operon (2, 9, 33). A betL knockout mutant and a mutant of gbu obtained by transposition were significantly affected in their abilities to accumulate glycine betaine and were unable to withstand concentrations of salt as high as the isogenic parent strain can withstand (18,30). Similarly, a mutant with an insertional inactivation of opuCA was defective in the uptake of carnitine and had impaired growth at high osmolarity (9, 33). Proline has been identified as an osmolyte for L. monocytogenes. The proline transport mechanism has not been characterized yet. However, the proBA operon, coding for the enzymes that catalyze the two first steps of proline biosynthesis, has recently been identified. Disru...

Genome-wide transcriptional profiling of the cell envelope stress response and the role of LisRK and CesRK in Listeria monocytogenes

“…The ctc gene (lmo0211) plays a protective role during osmotic stress and was found to be upregulated 5.5-fold by cefuroxime exposure (Gardan et al, 2003). Furthermore, the expression of the htrA gene (lmo0292) encoding the serine protease HtrA, was induced 18-fold by cefuroxime exposure, corresponding to the third most upregulated gene in this study (Supplementary Table S2).…”

Novel Roles of the Master Transcription Factors Spo0A and σBfor Survival and Sporulation ofBacillus subtilisat Low Growth Temperature

“…In this bacterium, the B -like transcription factor was induced by the cold shock (from 37 to 8°C) only 4 h following the temperature downshift, with a substantial increase in sigB expression after 6 h of that treatment (5). Furthermore, as is the case for sigB in B. subtilis, the induction of the B -like transcription factor of L. monocytogenes by other stresses (i.e., osmotic stress) at 37°C occurs during the 10 min that follows the stressing signal (12). Thus, we deduced that although sigB and spo0A are not components of the rapidly induced cold shock regulon of B. subtilis (6), they may constitute a second repertoire of genes induced during the vegetative growth of the adapting cell to the low growth temperature.…”

“…1B) reflected an upregulated activity of B during the logarithmic phase of the cold-shocked cultures. To check this possibility, we measured the activity of the B -dependent fusion ctc-lacZ, which is a traditional reporter of B activity (7,8,12). The expression of ctc was also dramatically induced after the cold shock (Fig.…”

Listeria monocytogenesσBRegulates Stress Response and Virulence Functions

“…The point labeled A represents lmo0880, which showed the largest difference in expression ratio. monocytogenes (this study) and B. subtilis (29,33), was recently shown to contribute to osmotolerance in L. monocytogenes (26).…”