Identification and expression of Lactobacillus paracasei genes for adaptation to desiccation and rehydration

Abstract

Lactobacillus paracasei is able to persist in a variety of natural and technological environments despite physico-chemical perturbations, in particular alternations between desiccation and rehydration. However, the way in which it adapts to hydric fluctuations and in particular the genetic determinants involved are not clearly understood. To identify the genes involved in adaptation to desiccation, an annotated library of L. paracasei random transposon mutants was screened for viability after desiccation (25% relative humidity, 25{degrees}C). Subsequently, the expression of the identified genes was measured at five stages of the dehydration-rehydration process to formulate the chronology of gene expression. The 24 identified genes were related to metabolism and transport, membrane function and structure, regulation of stress response, DNA related enzymes and environmental sensing. They were classified into four different transcriptomic profiles, in particular genes upregulated during both desiccation and rehydration phases and genes upregulated during the desiccation phase only. Thus, genetic response to hydric fluctuations seems to occur during desiccation and can continue or not during rehydration. The genes identified should contribute to improving the stabilization of lactobacillus starters in dry state.\n\nImportanceSince water is the fundamental component of all living organisms, desiccation and rehydration alternation is one of the most prevalent and severe stresses for most microorganisms. Adaptation to this stress occurs via a combination of mechanisms which depend on the genetic background of the microorganism. In L. paracasei, we developed a strategy to identify genes involved in the adaptation to hydric fluctuations using random transposon mutagenesis and targeted transcriptomics. Both dehydration and rehydration were studied to decipher the chronology of genetic mechanisms. We found 24 as yet unidentified genes involved in this response. Most of them are linked to either the transport of molecules or to cell wall structure and function. Our screening also identified genes for environment sensing and two alarmones necessary for L. paracasei survival. Furthermore, our results show that desiccation is a critical phase for inducing stress response in L. paracasei.