Effects of pH Changes on Zebrafish Microbiome

Abstract

The pH values of the different regions of the human gastrointestinal tract are known, though their effects on the prevalent microbiota in the respective regions are unknown. This is important to note because digestion in warm-blooded animals, like humans, can only occur within a restricted range of pH and temperature. Here we tested the effects of varying pH values on the microbiome of our model organisms: zebrafish embryos. A 16S rRNA sequencing analysis was performed to compare the relative abundance and the alpha diversity of the different bacterial families present in the zebrafish embryo gut. The derived microbial isolates of the two main bacterial genera under observation, Aeromonas and Vibrio, from the zebrafish embryo water were then assessed for growth by performing various bioassays to see the effects of pH level changes on growth related factors. It was hypothesized that Aeromonas, being an acidophile, would better grow and survive in acidic conditions and that Vibrio, being a basophile, would better grow and survive in basic conditions. The results obtained from the various bioassays indicated a higher relative fitness of Aeromonas compared to Vibrio. They also showed the tendency of Aeromonas to grow better in an acidic medium and that of Vibrio to grow better in a basic medium. Overall, the diversity of the microbiota increased due to changes in the pH value of the surroundings. This increase was observed to be greater with an acidic treatment (i.e., lowering of pH) compared to a basic treatment (i.e., increasing the pH).