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

RESEARCH ARTICLE Effects of woody forages on biodiversity and bioactivity of aerobic culturable gut bacteria of tilapia (Oreochromis niloticus) Feng Wu1,2, Biao Chen1,2, Sha Liu1,2, Xiongjian Xia1,2, Liuling Gao1,2, Xiaoyong ZhangID1,2*, Qing Pan1,2* 1 Joint Laboratory of Guangdong Province and Hong Kong Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University, Guangzhou, China, 2 Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou, China * zhangxiaoyong@scau.edu.cn (XZ); qpan@scau.edu.cn (QP) Abstract The present study investigated the effects of four woody forages (Moringa oleifera Lam (MOL), fermented MOL, Folium mori (FM) and fermented FM) on biodiversity and bioactivity of aerobic culturable gut bacteria of tilapia (Oreochromis niloticus) by a traditional culture- dependent method. A total of 133 aerobic culturable isolates were recovered and identified from the gut of tilapia, belonging to 35 species of 12 genera in three bacterial phyla (Firmi- cutes, Actinobacteria and Proteobacteria). Among them, 6 bacterial isolates of Bacillus baekryungensis, Bacillus marisflavi, Bacillus pumilus, Bacillus methylotrophicus, Proteus mirabilis and Pseudomonas taiwanensis were isolated from all the five experimental groups. The Bray-Curtis analysis showed that the bacterial communities among the five groups dis- played obvious differences. In addition, this result of bioactivity showed that approximate 43% of the aerobic culturable gut bacteria of tilapia displayed a distinct anti-bacterial activity

against at least one of four fish pathogens Streptococcus agalactiae, Streptococcus iniae, Micrococcus luteus and Vibrio parahemolyticus. Furthermore, Bacillus amyloliquefaciens and Streptomyces rutgersensis displayed strong activity against all four indicator bacteria. These results contribute to our understanding of the intestinal bacterial diversity of tilapia when fed with woody forages and how certain antimicrobial bacteria flourished under such diets. This can aid in the further exploitation of new diets and probiotic sources in aquaculture. Introduction Tilapia is popular among consumers in most regions and countries, with a global consumption and output that continue to increase [1, 2]. However, because of the large amount of tilapia cultured, even though the demand of fish meal in tilapia aquaculture is very low, the consump- tion of fish meal still accounts for a large proportion of the overall cost [3]. Although the fish meal is the best sources of quality proteins used in aquaculture diets, its application is limited PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0235560 July 2, 2020 1 / 17 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Wu F, Chen B, Liu S, Xia X, Gao L, Zhang X, et al. (2020) Effects of woody forages on biodiversity and bioactivity of aerobic culturable gut bacteria of tilapia (Oreochromis niloticus). PLoS ONE 15(7): e0235560. https://doi.org/10.1371/ journal.pone.0235560 Editor: Vijai Gupta, Tallinn University of Technology, ESTONIA Received: March 2, 2020 Accepted: June 17, 2020

Published: July 2, 2020 Copyright: © 2020 Wu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript. Funding: This study was financially supported by the Program of Department of Ocean and Fisheries of Guangdong Province, China (A201701C03 and GDME2018C014) and the National Natural Science Foundation of China (3177100038). Competing interests: The authors have declared that no competing interests exist.