Bacterial composition and inferring function profiles in the biofloc system rearing Litopenaeus vannamei postlarvae at a low salinity

Abstract

This study investigated the bacterial composition and inferring function profiles in the biofloc system rearing Litopenaeus vannamei postlarvae (PL) at a low salinity condition. PL (~ stage 15) were stocked in four parallel tanks filled in water with a salinity of 5.0‰ at a density of 4000 individuals per m3 for a 28-days culture experiment, during which glucose was added as a carbon source with a C:N of 20:1. At the end of the experiment, water was sampled from each tank and pooled to extract microbial DNA for high-throughput sequencing of the V3-V4 region of the 16S rRNA gene. Results showed that the bacterial community at 28 d was dominated by phyla of Proteobacteria (45.8%), Bacteroidetes (21.1%), Planctomycetes (13.5%), Chlamydiae (10.3%), and Firmicutes (6.8%). A proportion of 81% inferring KEGG functions of this bacterial community is associated with metabolism. Among functions relating to nitrogen metabolism, 48.5% were involved in converting ammonia to glutamate. Still, the proportion of those engaged in transformation among ammonia, nitrite, and nitrate was 18.0%, inferring higher protein-synthesis but lower inorganic nitrogen-transformation capacities of the bacterial community. At the same time (28 d), high levels of total nitrogen (231.3±6.0 mg L-1) and biofloc (127.0±63.0 mL L-1) but low concentrations of ammonia (0.04±0.01 mg L-1), nitrite (0.2±0.1 mg L-1) and nitrate (12.9±2.5 mg L-1) were observed. The results supply a novel insight for understanding bacterial community function in the biofloc system nursing L. vannamei PL at low salinity.