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Disruption by antibiotics causes instability to the native microbiota, which typically increases host susceptibility to opportunistic infections (e.g. C. diff) that result in correlated diseases, such as antibiotic-associated diarrhea in humans. Other animals such as vertebrate fish also possess an important microbiome residing in the outer mucosal skin layer, which provides essential protection to the host against the consent contact of the surrounding environment. Yet, after undergoing a disruptive event such as antibiotic exposure, our knowledge remains limited to predict how the microbial community will return and how the environment might influence the microbial assemblage during recovery. The focus of this study investigates whether the recovery environment influences the return of the skin microbiota after fish are briefly exposed to a strong dose of the broad-spectrum antibiotic rifampicin. To test this, we placed mosquitofish (Gambusia affinis) into different recovering conditions post-treatment for a week 1) a sterile mimic of pond water, Artificial Pond Water (APW) and 2) an environment where fish were housed in, aquarium tank water. During recovery, the fish skin microbiota and surrounding water were sampled to compare water type conditions. Additionally, two questions were explored 1) does the same taxon arise post-treatment when skin bacterial overgrowth occurs? 2) does the skin mucus layer increase during overgrowth of skin bacteria? Our findings, after rifampicin exposure, show that the recovery environment does influence the bacterial load and structural features (16S rRNA gene sequencing and ERIC-PCR fingerprint profiles) of the fish skin microbial community early in recovery, but later in the week begins to merge into similar microbial assemblages. On the contrary, Microgen ID strips testing the biochemical profile of the returning skin microbiome suggested that fish recovered in APW at 12 hr shared a more comparable profile similarity to pre-treatment-24 hr than to fish recovered in aquarium water. Water chemistry parameters tested with dip strips did not find any significant difference between the APW and aquarium water environments. Throughout recovery in different conditions, the surrounding water bacteria population reflected to the bacterial load found on the fish skin. Our findings showed the environment influences an antibiotic-disrupted fish skin microbiome early and at mid-recovery, but by the end of the week returns to similar outcomes., thus giving partial support to the main hypothesis. Research questions explored during mid-recovery at 60 hr, found that the bacterial load on fish recovered in APW significantly increased during which the genus Comamonas was suspected as the most abundant (52%) taxa, yet more data analysis is needed for confirmation. Staining fish skin mucus with alcian blue was not found to significantly increase on treated fish recovered in APW while bacterial numbers peaked at midrecovery.



Mosquitofish skin, Microbiome, Antibiotic, Environment, Recovery