Wild-type and cancer-prone zebrafish exhibit distinct gut microbial diversity and differential anti-inflammatory response upon infection.

The study investigated the gut microbial diversity and the role of gut-associated microorganisms in modulating the immune responses in normal (wild-type) and TP53 (cancer-prone) zebrafish. Biochemical tests, genus/species-specific PCR, and 16S rDNA sequencing were performed to characterize the bacteria isolated from the gut of wild-type (WT) and cancer-prone zebrafish. Gut microbiome analysis revealed greater diversity but reduced bacterial load in wild-type zebrafish compared with cancer-prone zebrafish, which had lesser diversity but higher bacterial load. Interestingly, the gut in cancer-prone fish showed selective colonization by opportunistic pathogens. The bacterial isolates showed resistance to antibiotics such as tetracycline, nalidixic acid, and ciprofloxacin. Gnotobiotic zebrafish embryos were established, and mono-colonization with the isolated bacteria was done to examine the expression of anti-inflammatory genes using real-time PCR. Variable expression of and was observed in germ-free (GF) wild-type embryos when mono-colonized with and . In contrast, germ-free mutant embryos showed a consistent downregulation of both the anti-inflammatory genes. Thus, a better immune response in WT embryos against or infection than in cancer-prone fish was observed, suggesting that genetic predisposition could contribute to disabling the immune system against infection.