Interestingly, σH-like factors appear to be more divergent across non-sporulating bacteria than in sporulating bacteria . At the same time, structural elements similar to the conserved Gram-positive DNA uptake machinery appeared to be encoded in
the genome in members of the Firmicutes not known for being naturally transformable, suggesting that this capacity may be more widespread than previously expected [12–14]. Two factors, classified in a single large SAR302503 supplier σH-family of sigma factors by Morikawa et al. , are directly involved in transcription of competence genes in non-sporulating bacteria: the well-known ComX of naturally transformable streptococci , and the product of the so-called sigH gene of
Staphylococcus aureus, a species which has not yet been shown to be transformable . These observations suggested the link between σH-like factors and genetic competence in non sporulating Firmicutes . L. sakei belongs to the microbiota that develops on meats under storage, especially during vacuum packing. It is largely used as a starter for the manufacture of fermented sausages in Western Europe and its potential use in meat product biopreservation is STA-9090 currently under study [16–18]. Survival of L. sakei ranges from one day in aerated selleck products chemically defined liquid medium, to a few months in dry sausages, although little is known about the factors determining its stability. The existence in L. sakei of sigH Lsa, an apparent sigH Bsu ortholog, led us to identify the gene set regulated by σLsa H, and to determine whether and how this regulator is implicated in competence and stationary phase survival. A strain allowing experimental sigH Lsa induction was constructed,
and used in a genome-wide microarray study. Genes activated by sigH Lsa overexpression appeared mainly involved in genetic competence, although we could not obtain evidence for natural transformation. else This study provides further suggestive evidence that the conserved role of the σH-like sigma factors in non-sporulating Firmicutes is to activate competence gene expression. Results and discussion Identification of sigH in the genome of L. sakei and other lactobacilli Automatic annotation of the L. sakei 23 K genome  identified LSA1677 as a coding sequence (CDS) of a putative alternative sigma factor of the σ70 superfamily. It belongs to COG1595 (E-value of 7e-6), which comprises both ECF-type sigma factors (E. coli RpoE homologs) and σH of B. subtilis, and thus reflects the reported structural proximity between ECF sigma factors and σBsu H [2, 4, 11]. The conserved genetic context of the L. sakei LSA1677 locus and the B. subtilis sigH locus, and more generally the local synteny between several members of the Firmicutes (Figure 1), revealed that LSA1677 and sigH Bsu are likely orthologous genes, belonging to a widespread family in the Firmicutes.