Kumari, Y. | bioRxiv Science

bioRxiv2026

Maltose aids in the growth of Salmonella Typhimurium in nitrogen-deficient conditions

Enteric pathogens, such as Salmonella, encounter uncertain nutrients in both the host and the environment. Nutrients such as carbon and nitrogen are essential for growth, and when these nutrients are limited, bacteria have developed various mechanisms to overcome stress and thrive in nutrient-rich environments. In this study, we investigated the role of the disaccharide sugar maltose in the growth and pathogenicity of Salmonella Typhimurium (STM) under nitrogen-deficient culture conditions. Throughout the study, we used Burks medium to mimic nitrogen-deficient conditions. STM growth in Burks medium was minimal, and maltose supplementation enhanced STM growth in both liquid and solid Burks media. The STM grown in Burks medium had a reduced bacterial cell length, which increased upon the addition of maltose and became comparable to that of LB-grown STM WT. Growth was dependent on the NtrBC two-component system and sigma factor RpoE. Deletion of ntrB and rpoE significantly reduced the growth in Burks medium during the log phase. Salmonella grown in Burks medium with maltose had reduced invasion in Caco-2 cells, phagocytosis in RAW 264.7 macrophages, and organ burden in C57BL/6 mice. Our findings revealed the role of maltose in enhancing the growth and length of Salmonella under nitrogen-deficient conditions. However, Salmonella grown in Burks medium with maltose is defective in pathogenesis.

microbiology↗

bioRxiv2024

The resilience of Salmonella to bile stress is impaired due to the reduced efflux pump activity mediated by the antioxidant enzyme YqhD

Bile salts play a critical role in modulating the host gut. They have antimicrobial properties wherein they disrupt the bacterial membrane and produce reactive oxygen species, causing DNA damage. Bile-resistant pathogen like Salmonella regulates their metabolic activity to counteract the effects of bile. This study explores the role of YqhD, a putative alcohol dehydrogenase, in Salmonellas bile salt susceptibility. We observed increased survival of yqhD mutant in the in vitro studies in LB media with bile, liver cell line HepG2 and C57BL/6 mice on treatment with 8% sodium cholate in the intestine. Bile salts are produced for the digestion of fat. Replacing the chow diet with a high-fat diet (HFD) in mice increased organ burden in C57BL/6 mice of the yqhD mutant. Mutation of yqhD on bile salt exposure leads to increased reactive oxygen species and modulation of antioxidant genes in the bacteria. The oxidative stress of the yqhD mutant is indispensable for improved survival when exposed to bile salt. The addition of antioxidant glutathione in vitro reduced the enhanced growth of the yqhD mutant. Similarly, in the gp91-/- phox mice, there was a reduced organ burden of yqhD mutant on exposure to HFD compared to chow-fed mice. Furthermore, the yqhD mutant increases AcrAB efflux pump activity regulated by RamA/R regulon. TeaserRedox gene yqhD regulates bile salt susceptibility by modulating Salmonellas ROS and efflux pump activity. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=185 SRC="FIGDIR/small/625033v1_figa1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@14e30f0org.highwire.dtl.DTLVardef@6f14a0org.highwire.dtl.DTLVardef@b3291dorg.highwire.dtl.DTLVardef@503988_HPS_FORMAT_FIGEXP M_FIG A. STM {Delta}yqhD has less organ burden in the C57BL/6 mice than STM WT, and there was a similar organ burden in gp91phox-/-. On HFD exposure, the organ burden of STM {Delta}yqhD became similar to STM WT in C57BL/6 mice, and there was reduced organ of STM {Delta}yqhD burden when gp91phox-/- were exposed to HFD. B. On bile salt exposure, YqhD in Salmonella reduces ROS in bacteria and expression of RamA, decreasing the AcrAB efflux pump activity and reducing survival. C_FIG

microbiology↗