The cAMP receptor protein (CRP) enhances the competitive nature of Salmonella Typhimurium

Abstract

The cAMP receptor protein (CRP) is a global regulatory protein. We evaluated the role of CRP in starvation physiology in Salmonella Typhimurium. The Δcrpmutant survived 10days of starvation. However, in a co-culture with the wild type in nutrient-rich medium, Δcrpdied within 48h. Similar co-culture results were observed with Escherichia coli and Staphylococcus aureus. Our study showed that the Δcrpmutant was not killed by toxins and the Type IV secretion system of the WT. The possibility of viable but non-culturable cells (VBNC) was also ruled out. However, when the overall metabolism of the co-culture was slowed down (anaerobic condition, inhibition by antibiotics and low temperature) that improved the survival of Δcrpin co-culture. But one more significant observation was that the Δcrpmutant survived in nutrient-free co-culture conditions. These two observations suggest that CRP protein is essential for efficient nutrient assimilation in a competitive environment. The cells without CRP protein are unable to evaluate the energy balance within the cell, and the cell spends energy to absorb nutrients. But the wild type cell absorbs nutrients at a faster rate than Δcrpmutant. This leads to a situation wherein the Δcrpis spending energy to absorb the nutrients but is unable to compete with the wild type. This futile metabolism leads to death. Hence, this study shows that CRP is a metabolism modulator in a complex nutrient environment. This study also highlights the need for innovative growth conditions to understand the unique function of a gene.