Effects of woody forages on biodiversity and bioactivity of aerobic culturable gut bacteria of tilapia (Oreochromis niloticus)

isolates were tested against 4 indicator bacteria to examine their antibacterial activity against four fish pathogens including Streptococcus agalactiae, Streptococcus iniae, Micrococcus luteus and Vibrio parahemolyticu. The results (Table 5) revealed that 15 species (42.86%) displayed antibacterial activity against at least one indicator bacteria of the four pathogens. And, over 14% (5 species) of bioactive isolates displayed strong activity against the three and more indi- cator bacteria. Furthermore, Bacillus amyloliquefaciens SCAU-070 and Streptomyces rutgersen- sis SCAU-102 displayed strong activity against all four indicator bacteria, MIC values are 6.2– 25 μg / ml and 3.1–25μg / ml, respectively (Table 6). Among them, the inhibitory effect of Bacillus amyloliquefaciens SCAU-070 on Streptococcus. iniae was the strongest, and the zone of inhibition reached 17.8 mm. Discussion Ingestion has an important effect on the intestinal microbes and their functions in tilapia [52]. And, the microbiota can also affect behaviors [53], including feeding behavior, digestive/ absorptive processes (e.g., by modulating intestinal motility and the intestinal barrier) [54], metabolism, as well as the immune response, with repercussions on the energy homeostasis, growth status [55] and health of the host. Research by Dhaneshwaree Asem et al. has shown that bacterial strains residing in the gastrointestinal region of non-ruminant swine are a prom- ising source for lignocellulose degrading microorganisms that could be used for biomass con-

version. And, few reports have investigated directly the relationships between feeding tilapia Fig 1. Neighbor-joining phylogenetic tree from analysis of the 16s rRNA sequences of culturable bacteria isolated from intestines of tilapia fed woody forage. The numbers at nodes were percentages indicating the levels of bootstrap support, based on a neighbor joining analysis of 1000 resampled datasets. Only values > 50% were shown. Scale bar: 0.02 substitutions per nucleotide position. https://doi.org/10.1371/journal.pone.0235560.g001 Fig 2. The intestinal bacteria communities at genus level. The color-coded bar plot showed the numbers of isolates of 12 genera in 5 groups. https://doi.org/10.1371/journal.pone.0235560.g002 PLOS ONE Effects of wood forages on gut bacterial biodiversity and bioactivity in tilapia PLOS ONE | https://doi.org/10.1371/journal.pone.0235560 July 2, 2020 8 / 17