Effect of lactose starvation on the physiology of Lactobacillus casei GCRL163

Lactobacillus casei is widely used in fermented food (e.g. cheese, milk and others). On this basis, maximising viability throughout the physiological challenges of food processing and storage is desirable so that they may be delivered to the hosts gut alive. One of these challenges is surviving carbohydrate depleting during cheese maturation. In this study, L. casei GCRL163 was used to investigate the physiology of slow growth and characterise the protein expression during lactose starvation similar to those that would occur during cheese maturation. Proteomic analysis was undertaken using gel-based (1D-SDS-PAGE) and gel-free (1D-LC-MS/MS) to explain the physiological changes occurring during growth in modified MRS (mMRS) with different levels of lactose (0% lactose, starvation; 0.2% lactose, growth limiting; 1% lactose, no grow limited, control). Better survival was observed in lactose free mMRS relative to the control. Differential expression of proteins in starved cells was observed and indicated an association with lactose metabolism. 1D-LC-MS/MS revealed that several important metabolic pathways associated with galactose and glycolysis/ gluconeogenesis metabolism were significantly down-regulated in 0% lactose. In contrast, other pathways related to amino acid and carbohydrate metabolism associated with pyruvate and arginine were significantly up-regulated in 0% lactose. The data suggests that starved L. casei induce several pathway likely targeted at cellular energy production. Explaining the adaptation of L. casei during lactose starvation will assist efforts to increase viability of L. casei and allow the organism to function as a beneficial dietary adjunct.