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Some lactic acid bacteria, especially Lactobacillus spp., possess adhesive properties enabling colonization of the human gastrointestinal tract. Two probiotic Lactobacillus plantarum strains, WCSF1 and 299v, display highly different mannose-specific adhesion, with L. plantarum 299v being superior to L. plantarum WCFS1 based on a yeast agglutination assay. A straightforward correlation between the mannose adhesion capacity and domain composition of the mannose-specific adhesin (Msa) in the two strains has not been demonstrated previously. In this study, we analyzed the promoter regions upstream of the msa gene encoding a mannose-specific adhesin in these two strains. The promoter region was mapped by primer extension and DNA sequence analysis, and only a single nucleotide change was identified between the two strains. However, Northern blot analysis showed a stronger msa transcript band in 299v than in WCFS1 correlating with the different adhesion capacities. During the establishment of a high-throughput yeast agglutination assay, we isolated variants of WCFS1 that displayed a very strong mannose-specific adhesion phenotype. The region upstream of the msa gene in these variants showed an inversion of a 104-bp fragment located between two perfectly inverted repeats present in the untranslated leader region. The inversion disrupts a strong hairpin structure that otherwise most likely would terminate the msa transcript. In addition, the ribosome binding site upstream of the msa gene, which is also masked within this hairpin structure, becomes accessible upon inversion, thereby increasing the frequency of translation initiation in the variant strains. Furthermore, Northern blot analysis showed a higher abundance of the msa transcript in the variants than in the wild type, correlating with a strong-Msa phenotype.IMPORTANCE Probiotic strains possess adhesive properties enabling colonization of the human intestinal tract through interactions between molecules present on the probiotic bacteria and components of the epithelial surface. In Lactobacillus plantarum, interaction is mediated through bacterial surface proteins like Msa, which binds to mannose residues present on the intestinal cells. Such interactions are believed to be important for the health-promoting effects of probiotics, including displacement of pathogens, immunomodulation, and protective effects on the intestinal barrier function. In this study, we have identified a new molecular switch controlling expression of the msa gene in L. plantarum strain WCFS1. Strains with increased msa expression could be valuable in the development and manufacture of improved probiotic products. [ABSTRACT FROM AUTHOR]

Although carbon dioxide (CO2) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high COz concentrations at refrigeration temperatures. We examined the listeriai responses of different strains to growth in air, 100% N2, and 100% CO2. The CO2-induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to COz as to other anaerobic, slightly acidic environments (100% N2, pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO2 and N2 at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO2-containing atmospheres. Together, our findings demonstrate that the CO2response is a partly strain-dependent complex mechanism. The possible links between the CO2-dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed. [ABSTRACT FROM AUTHOR]

Although carbon dioxide (CO(2)) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high CO(2) concentrations at refrigeration temperatures. We examined the listerial responses of different strains to growth in air, 100% N(2), and 100% CO(2). The CO(2)-induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to CO(2) as to other anaerobic, slightly acidic environments (100% N(2), pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO(2) and N(2) at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO(2)-containing atmospheres. Together, our findings demonstrate that the CO(2)-response is a partly strain-dependent complex mechanism. The possible links between the CO(2)-dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed.