Understanding the starvation adaptation of Lactobacillus casei through proteomics

Food microbes are exposed to several stress conditions in natural environments, which can have an effect on performances. Lactobacilli are highly adaptive group of food microbes which are able to survive in various environmental niches, including ones where preferred nutrients are deficient. This study was conducted to investigate the adaptation to lactose starvation in Lactobacillus casei using comparative proteomics. One-dimensional sodium dodecyl sulphate-polyacrylamide (1-D SDS PAGE) and two-dimensional electrophoresis (2-DE) were performed on L. casei cells cultivated in a semi-defined medium, with different initial levels of lactose, up to 8 days. Clear visual changes in the 1-D SDS PAGE profiles were seen for cells cultured in 0% lactose. The relative expression of xylulose-5-phosphate phosphoketolase, elongation factor G and DnaK increased in lactose starved cells during stationary phase when compared to the temporal expression of these proteins in cytosolic fraction of cells cultured in 0.2 or 1% lactose. Comparative spot analysis of 2-DE gels showed that 13 proteins were over expressed in lactose starved cells (0% lactose). Of these up-regulated proteins, nine were identified by MALDI-TOF/TOF mass spectrometry with functionalities in protein synthesis, general stress responses and carbohydrate metabolism, where enzymes involved in glycolysis, pyruvate metabolism and the pentose phosphate pathway were up-regulated. These results suggested that proteomic analysis can provide useful information on adaptation of lactobacilli. Identification of specific protein markers that involve in adaptation to a specific stress factor would be help in selecting strains with better performance in a given application of these beneficial food microbes.