Expressão e atividade de sistemas de dois componentes (TCS) de Salmonella enterica sorovar Typhimurium no contexto do metaboloma

Abstract

The interaction between members of the human gut microbiome, host cells and invading pathogens often occurs through small molecules, also called metabolites. The perception and effective response of a microorganism to the different conditions found in its environment, including metabolites produced by other microbes, is important for its adaptation, survival and dissemination. Two-component systems (TCS) allow the perception and response to environmental changes by regulating the expression of specific genes. Our group previously showed that organic extracts of human feces (EF) as well as the specific metabolite 3,4-dimethylbenzoic acid (3,4-DMB) found within the EF, inhibit the ability of Salmonella enterica sorovar Typhimurium to invade host cells. In the present work, we investigated the impact of the human gut microbiome as well as small molecules produced by Clostridium citroniae (a member of this microbiome) on the expression and activity of Salmonella TCS genes. Metabolites (from feces or C. citroniae cultures) were extracted using ethyl acetate and added to culture medium. The pH of the medium was adjusted (~7.4), and the solution was filter sterilized. Salmonella was grown in the presence or absence of the organic extracts as well as 3,4-DMB acid under aerobic and anaerobic conditions until it reached mid-log growth. RNA was then extracted for Real-time PCR using primers targeting almost all Salmonella TCS. Our results showed that several TCS involved in Salmonella virulence (SsrAB, EnvZ-OmpR, QseCB, PhoQP, TorSR, TtrRS) were differentially regulated by these metabolites both in aerobic and anaerobic conditions. EnvZ-OmpR, PhoPQ, and SsrAB are directly involved in the regulation of Salmonella Pathogenicity Islands 1 and 2. QseCB is crucial for Salmonella =quorum sensing, sensing of host hormones and regulation of swimming motility. Several other TCS were also regulated, including TorSR and TtrRS, which are involved in the anaerobic respiration of trimethylamine N-oxide (TMAO) and tetrathionate, respectively. These compounds are important for Salmonella survival in the anaerobic environment of the human gut. Our results of the evaluation of global Salmonella gene expression grown in the presence of 3,4-DMB acid (aerobiosis and anaerobiosis) as well as in the presence of EF in anaerobiosis, showed that genes encoded in SPI-1 and SPI-2, SPI-4 and some TCS genes have been repressed, while multiple drug resistance genes, as well marR, marB and marA genes have been activated under these conditions. Besides, we compared our results of RNAseq, Salmonella was grown in the presence of 3,4-DMB acid in aerobiosis, with results available from the Salmonella Compendium database. Also, Salmonella's ability to enter and survive within phagocytic cells (macrophages RAW 264.7) appears to be affected by the three conditions tested in this work. Our results show that important Salmonella virulence signalling pathways can be modulated by the metabolites present in the human intestinal microbiome and open the way for further research on the microbiome-pathogen intercellular signalling in the intestinal environment.