Peeling back the layers of competitive exclusion using Salmonella as a model
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PROVIDER: PRJNA1087266 | ENA |
REPOSITORIES: ENA
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Project description:An ex vivo system was developed to monitor Salmonella growth, virulence (SPI1 expression) and gene expression (measured by microarray) in response to the permissive and exclusive communities. Yellow fluorescent protein (yfp) and cyan fluorescent protein (cfp) variants were fused to the rrn growth-dependent promoter and the hilA operon (SPI-1 cell invasion locus), respectively, in Salmonella. Fluorescence associated with the YFP and CFP reporters was used to monitor Salmonella growth and SPI1 virulence gene expression in co-culture with cecal communities ex vivo. The Salmonella reporter strain was grown in dialysis tubing in a simulated cecal medium, ex vivo cecal contents (EVCC), submerged in permissive or exclusive communities, to enable collection of Salmonella cells for study. Initially, the fluorescent reporters were used to empirically determine the earliest time point at which the exclusive community had the most significant impact on Salmonella growth or virulence expression relative to the permissive community, which was six-hour co-culture of the reporter strain with the communities. Cells were harvested at that time point for gene expression comparisons. Genes within metabolic pathways that were differentially expressed in permissive vs. exclusive communities were subsequently deleted in Salmonella and mutants’ growth dynamics when cocultured with the exclusive community were monitored over 48 hours using a fluorescence plate reader.
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Project description:Baby chicks administered a fecal transplant from adult chickens are resistant to Salmonella colonization by competitive exclusion. A two-pronged approach was used to investigate the mechanism of this process. First, Salmonella response to an exclusive (Salmonella competitive exclusion product, Aviguard®) or permissive microbial community (chicken cecal contents from colonized birds containing 7.85 Log10Salmonella genomes/gram) was assessed ex vivo using a S. typhimurium reporter strain with fluorescent YFP and CFP gene fusions to rrn and hilA operon, respectively. Second, cecal transcriptome analysis was used to assess the cecal communities' response to Salmonella in chickens with low (≤5.85 Log10 genomes/g) or high (≥6.00 Log10 genomes/g) Salmonella colonization. The ex vivo experiment revealed a reduction in Salmonella growth and hilA expression following co-culture with the exclusive community. The exclusive community also repressed Salmonella's SPI-1 virulence genes and LPS modification, while the anti-virulence/inflammatory gene avrA was upregulated. Salmonella transcriptome analysis revealed significant metabolic disparities in Salmonella grown with the two different communities. Propanediol utilization and vitamin B12 synthesis were central to Salmonella metabolism co-cultured with either community, and mutations in propanediol and vitamin B12 metabolism altered Salmonella growth in the exclusive community. There were significant differences in the cecal community's stress response to Salmonella colonization. Cecal community transcripts indicated that antimicrobials were central to the type of stress response detected in the low Salmonella abundance community, suggesting antagonism involved in Salmonella exclusion. This study indicates complex community interactions that modulate Salmonella metabolism and pathogenic behavior and reduce growth through antagonism may be key to exclusion.
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Project description:BackgroundDespite a long history of investigation, considerable debate revolves around whether Neanderthals became extinct because of climate change or competition with anatomically modern humans (AMH).Methodology/principal findingsWe apply a new methodology integrating archaeological and chronological data with high-resolution paleoclimatic simulations to define eco-cultural niches associated with Neanderthal and AMH adaptive systems during alternating cold and mild phases of Marine Isotope Stage 3. Our results indicate that Neanderthals and AMH exploited similar niches, and may have continued to do so in the absence of contact.Conclusions/significanceThe southerly contraction of Neanderthal range in southwestern Europe during Greenland Interstadial 8 was not due to climate change or a change in adaptation, but rather concurrent AMH geographic expansion appears to have produced competition that led to Neanderthal extinction.
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