Peeling back the many layers of competitive exclusion.

Baby chicks administered a fecal transplant from adult chickens are resistant to colonization by competitive exclusion. A two-pronged approach was used to investigate the mechanism of this process. First, response to an exclusive ( competitive exclusion product, Aviguard) or permissive microbial community (chicken cecal contents from colonized birds containing 7.85 Log genomes/gram) was assessed using a reporter strain with fluorescent YFP and CFP gene fusions to and operon, respectively. Second, cecal transcriptome analysis was used to assess the cecal communities' response to in chickens with low (≤5.85 Log genomes/g) or high (≥6.00 Log genomes/g) colonization. The experiment revealed a reduction in growth and expression following co-culture with the exclusive community. The exclusive community also repressed 's SPI-1 virulence genes and LPS modification, while the anti-virulence/inflammatory gene was upregulated. transcriptome analysis revealed significant metabolic disparities in grown with the two different communities. Propanediol utilization and vitamin B12 synthesis were central to metabolism co-cultured with either community, and mutations in propanediol and vitamin B12 metabolism altered growth in the exclusive community. There were significant differences in the cecal community's stress response to colonization. Cecal community transcripts indicated that antimicrobials were central to the type of stress response detected in the low abundance community, suggesting antagonism involved in exclusion. This study indicates complex community interactions that modulate metabolism and pathogenic behavior and reduce growth through antagonism may be key to exclusion.