STM1863, a Member of the DUFs Protein Family, Is Involved in Environmental Adaptation, Biofilm Formation, and Virulence in Salmonella Typhimurium.

Salmonella Typhimurium (STM) is an important zoonotic Gram-negative pathogen that can cause infection in a variety of livestock and poultry. Meanwhile, as an important foodborne pathogen, the bacterium can survive in various stressful environments and transmits through the fecal-oral route, posing a serious threat to global food safety. To investigate the roles of STM1863, a member of the DUFs protein family, involved in STM environmental adaptation, biofilm formation, and virulence. We analyzed the molecular characteristics of the protein encoded by STM1863 gene and examined intra- and extracellular expression levels of STM1863 gene in mouse macrophages. Furthermore, we constructed STM1863 gene deletion and complementation strains and determined its environmental adaptation under stressful conditions such as acid, alkali, high salt, bile salt, and oxidation. And the capacity of biofilm formation and pathogenicity of those strains were analyzed and compared. In addition, the interaction between the promoter of STM1863 gene and RcsB protein was analyzed using DNA gel electrophoresis migration assay (electrophoretic mobility shift assay [EMSA]). The experiments revealed that acid adaptability and biofilm formation ability of STM1863 gene deletion strain were significantly weakened compared with the parental and complementary strains. Moreover, the adhesion and invasion ability of STM1863 deletion strain to mouse macrophages was significantly decreased, while the median lethal dose (LD50) increased by 2.148-fold compared with the parental strain. In addition, EMSA confirmed that RcsB protein could bind to the promoter sequence of STM1863 gene, suggesting that the expression of STM1863 gene might be modulated by RcsB. The present study demonstrated for the first time that STM1863, a member of the DUFs protein family, is involved in the modulation of environmental adaptation, biofilm formation, and virulence.

A Novel LysR Family Factor STM0859 is Associated with The Responses of Salmonella Typhimurium to Environmental Stress and Biofilm Formation.

Salmonella enterica subsp. enterica serovar Typhimurium (ST) is an intracellularly parasitic bacterium. This zoonotic pathogen causes food poisoning and thus imposes a severe threat to food safety. Here, to understand the regulatory roles of the novel transcription factor STM0859 on the response of ST to environmental stress and biofilm formation, the STM0859 gene-deficient strain and the complementation strain ΔSTM0859/STM0859 were generated, respectively. Then, its capacity of responding to environmental stresses and biofilm (BF) formation ability under different stresses, including acid, alkali, high salt, cholate, and oxidative stresses was tested. We further analyzed the interaction between the STM0859 protein and the promoter of the acid stress response-related gene rcsB by performing an electrophoresis mobility shift assay (EMSA). The results showed that acid resistance and BF formation capacities of ST-ΔSTM0859 strain were significantly weaker, as compared with those of Salmonella Typhimurium SL1344 (ST-SL1344) wild strain (p < 0.01). Quantitative qRT-PCR analysis showed that the expression levels of acid stress and BF formation-related genes, rcsB and rpoS, of ST-ΔSTM0859 strain were significantly reduced at the transcription levels, while the transcription levels of these genes were fully restored in complementation strain ST-ΔSTM0859/STM0859. The results of EMSA showed that STM0859 was capable of binding the promoter DNA fragments of the rcsB gene, suggesting that STM0859 can promote the transcription of the rcsB gene through interaction with its promoter, thereby exerting an indirectly regulatory role on the adaptive responses to acid stress and BF formation of ST. This study provided new insights into the regulatory mechanisms of the LysR family factors on the tolerances of ST under adverse environmental stresses.