The status of RpoS impacts the 2-aminoacrylate stress paradigm in ridA mutants of Salmonella enterica serovar Typhimurium

ABSTRACT Bacterial metabolism is composed of a complex system of anabolic and catabolic processes, and productive growth results from the regulated interplay of these processes. Genetic and biochemical studies on the LT2 type strain of Salmonella enterica serovar Typhimurium determined the need for RidA to prevent metabolic stress caused by 2-aminoacrylate (2AA). RidA is an enamine deaminase, and in its absence, 2AA accumulates and can irreversibly damage critical pyridoxal 5′-phosphate-dependent enzymes. Unexpectedly, the disruption of ridA in a virulent type strain ( S. enterica serovar Typhimurium strain 14028s) did not replicate the serine sensitivity observed in LT2. Consistent with reported differences between these strains, the status of rpoS impacted the phenotypes caused by a ridA mutation. Specifically, serine sensitivity in the 14028s strain background occurred only when an insertion in rpoS was combined with a mutation in ridA . Further data suggest the 14028s rpoS ridA growth deficiency is due to poor expression of sdaA , which encodes an Fe-S cluster serine deaminase. Additional combinatorial effects of lesions in ridA and rpoS indicate that the functional status of RpoS modulates the metabolic network in multiple ways that impact the cellular response to 2AA. IMPORTANCE RidA is an enamine/imine deaminase known for mediating 2-aminoacrylate (2AA)-induced stress in several bacterial models. Best characterized in S. enterica , manipulations to RidA have been used to probe metabolic flux in various bacteria. Here, we find that a key factor in the manifestation of 2AA stress is the status of transcriptional regulator RpoS. Our results indicate that a functional RpoS mediates some of the stress induced by exogenous serine in a ridA mutant strain and further implicates this regulator in modulating the metabolic network. These results bolster our understanding of the flux and robustness integral to bacterial metabolism and emphasize a need to better understand the involvement of the RpoS regulon.