Abstract
An inverse PCR strategy based on degenerate primers has been used to identify new genes of the cold shock protein family in Lactobacillus plantarum. In addition to the two previously reported cspL and cspP genes, a third gene, cspC, has been cloned and characterized. All three genes encode small 66-amino-acid proteins with between 73 and 88% identity. Comparative Northern blot analyses showed that the level of cspL mRNA increases up to 17-fold after a temperature downshift, whereas the mRNA levels of cspC and cspP remain unchanged or increase only slightly (about two- to threefold). Cold induction of cspL mRNA is transient and delayed in time as a function of the severity of the temperature downshift. The cold shock behavior of the three csp mRNAs contrasts with that observed for four unrelated non-csp genes, which all showed a sharp decrease in mRNA level, followed in one case (bglH) by a progressive recovery of the transcript during prolonged cold exposure. Abundance of the three csp mRNAs was also found to vary during growth at optimal temperature (28 degrees C). cspC and cspP mRNA levels are maximal during the lag period, whereas the abundance of the cspL transcript is highest during late-exponential-phase growth. The differential expression of the three L. plantarum csp genes can be related to sequence and structural differences in their untranslated regions. It also supports the view that the gene products fulfill separate and specific functions, under both cold shock and non-cold shock conditions.