CRP improves the survival and competitive fitness of Salmonella Typhimurium under starvation by controlling the cellular maintenance rate

Abstract

ABSTRACT Catabolite repression is a mechanism of selectively utilizing preferred nutrient sources by redirecting the metabolic pathways. Therefore, it prevents non-essential energy expenditure by repressing the genes and proteins involved in the metabolism of other less favored nutrient sources. Catabolite repressor protein (CRP) is a chief mediator of catabolite repression in microorganisms. In this context, we investigated the role of CRP in starvation tolerance, at both cell physiology and molecular level, by comparing the growth, survival, competitive fitness, maintenance rate, and gene and protein expression of wild type (WT) and ∆ crp of Salmonella Typhimurium, under nutrient-rich and minimal medium condition. The ∆ crp shows slow growth upon the arrival of nutrient-limiting conditions, poor survival under prolong-starvation, and inability to compete with its counterpart WT strain in nutrient-rich [Luria broth (LB)] and glucose-supplemented M9 minimal medium. Surprisingly, we observed that the survival and competitive fitness of ∆ crp are influenced by the composition of the growth medium. Consequently, compared to the glucose-supplemented M9 medium, ∆ crp shows faster death and a higher maintenance rate in the LB medium. The comparative gene and protein expression studies of WT and ∆ crp in LB medium show that ∆ crp has partial or complete loss of repression from CRP-controlled genes, resulting in a high abundance of hundreds of proteins in ∆ crp compared to WT. Subsequently, the addition of metabolizable sugar or fresh nutrients to the competing culture showed extended survival of ∆ crp . Therefore, our results suggest that CRP-mediated gene repression improves starvation tolerance and competitive fitness of Salmonella Typhimurium by adapting its cellular maintenance rate to environmental conditions. IMPORTANCE Salmonella Typhimurium is a master at adapting to chronic starvation conditions. However, the molecular mechanisms to adapt to such conditions are still unknown. In this context, we have evaluated the role of catabolite repressor protein (CRP), a dual transcriptional regulator, in providing survival and competitive fitness under starvation conditions. Also, it showed an association between CRP and nutrient composition. We observed that Δ crp growing on alternate carbon sources has lower survival and competitive fitness than Δ crp growing on glucose as a carbon source. We observed that this is due to the loss of repression from the glucose and CRP-controlled genes, resulting in elevated cellular metabolism (a high maintenance rate) of the Δ crp during growth in a medium having a carbon source other than glucose (e.g., Luria broth medium).