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a malolactic bacterium, the synthesis of a stress protein called LO18 with an apparent molecular mass of 18 kDa was greatly induced after heat (42°C), acid (pH 3) or ethanolic (12% (v/v)) shocks. Moreover, the LO18 protein synthesis was induced in stationary growth phase and was detected for a long time (30 h) during this growth phase. Significant identity was found between the N-terminal parts of the LO18 protein and the Hsp18 from Clostridium acetobutylicum suggesting that LO18 protein belongs to the family of small heat shock proteins conserved in prokaryotic and eukaryotic cells.

In Leuconostoc oenos, different stresses such as heat, ethanol, and acid shocks dramatically induce the expression of an 18-kDa small heat shock protein called Lo18. The corresponding gene (hsp18) was cloned from a genomic library of L. oenos constructed in Escherichia coli. A 2.3-kb DNA fragment carrying the hsp18 gene was sequenced. The hsp18 gene encodes a polypeptide of 148 amino acids with a calculated molecular mass of 16,938 Da. The Lo18 protein has a significant identity with small heat shock proteins of the alpha-crystallin family. The transcriptional start site was determined by primer extension. This experiment allowed us to identify the promoter region exhibiting high similarity to consensus promoter sequences of gram-positive bacteria, as well as E. coli. Northern blot analysis showed that hsp18 consists of a unique transcription unit of 0.6 kb. Moreover, hsp18 expression seemed to be controlled at the transcriptional level. This small heat shock protein was found to be peripherally associated with the membrane of L. oenos.

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Oenococcus oeni is a lactic acid bacterium which is able to grow in wine and perform malolactic fermentation. To survive and grow in such a harsh environment as wine, O. oeni uses several mechanisms of resistance including stress protein synthesis. The molecular characterisation of three stress genes hsp18, clpX, trxA encoding for a small heat shock protein, an ATPase regulation component of ClpP protease and a thioredoxin, respectively, allow us to suggest the existence in O. oeni of multiple regulation mechanisms as is the case in Bacillus subtilis. One common feature of these genes is that they are expressed under the control of housekeeping promoters. The expression of these genes as a function of growth is significantly different. Surprisingly, the clpX gene, which is induced by heat shock, was highly expressed in the early phase of growth. In addition to stress protein synthesis, adaptation to the acid pH of wine requires efficient cellular systems to extrude protons. Using inhibitors specific for different types of ATPases, we demonstrated the existence of H+-ATPase and P-type ATPase.

The food pathogen Bacillus cereus is likely to encounter acidic environments (i) in food when organic acids are added for preservation purposes, and (ii) during the stomachal transit of aliments. In order to characterise the acid stress response of B. cereus ATCC14579, cells were grown in chemostat at different pH values (pH(o) from 9.0 to 5.5) and different growth rates (micro from 0.1 to 0.8 h(-1)), and were submitted to acid shock at pH 4.0. Cells grown at low pH(o) were adapted to acid media and induced a significant acid tolerance response (ATR). The ATR induced was modulated by both pH(o) and micro, and the micro effect was more marked at pH(o) 5.5. Intracellular pH (pH(i)) was affected by both pH(o) and micro. At a pH(o) above 6, the pH(i) decreased with the decrease of pH(o) and the increase of micro. At pH(o) 5.5, pH(i) was higher compared to pH(o) 6.0, suggesting that mechanisms of pH(i) homeostasis were induced. The acid survival of B. cereus required protein neo-synthesis and the capacity of cells to maintain their pH(i) and DeltapH (pH(i) - pH(o)). Haemolysin BL and non-haemolytic enterotoxin production were both influenced by pH(o) and micro.

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Sequencing of the DNA region located upstream of the a-acetolactate synthase and decarboxylase (alsS-alsD) cluster of Oenococcus oeni allowed identification of an ORF, named trxA. This encodes a protein of 104 amino acids very similar to known thioredoxins. The protein encoded by the cloned fragment was able to complement Escherichia coli strains lacking a functional thioredoxin. Considering the results of protein sequence comparisons and complementation experiments, it was concluded that the trxA gene encodes a functional thioredoxin. Studies of trxA expression showed that the abundance of trxA mRNA was similar during all growth stages. A significant increase in trxA mRNA levels was observed in the presence of hydrogen peroxide in the medium or after heat shock. A single transcriptional start site was determined with total RNA isolated from cells subjected or not subjected to oxidative stress or heat shock. In each case the same promoter region was identified and shown to have a high similarity to the consensus promoter sequence of Grampositive bacteria, as well as to that of €, coli and the previously mapped promoters from 0. oeni.