Bacillus velezensis LG37 absorbs and utilizes ammonia nitrogen from aquaculture water and enhances the toxicity tolerance of grass carp (Ctenopharyngodon idella) to ammonia (non-ionic ammonium)

Abstract

High concentrations of ammonia nitrogen lead to multi-organ damage, decreased immunity, and metabolic disorders in aquaculture animals, which cause disease outbreaks. This study mainly screened probiotic strains for good control of the concentration of ammonia nitrogen and identified strain LG37 as Bacillus velezensis according to its morphological, 16S rDNA, phylogenetic, and genomic data analysis. This LG37 strain achieved efficiently purifies aquaculture water and enhances the toxicity tolerance of grass carp to ammonia. The experimental on growth characteristics showed that LG37 exhibited a satisfactory growth trend with 10 types of sugar, 17 types of amino acids, and 6 types of organic nitrogen as the carbon or nitrogen source. Under the conditions of initial dissolved oxygen at 6±1 mg/L, the temperature at 27±2°C, and pH 7±0.3. Through wastewater treatment equipment, which degraded ammonia nitrogen and the feed protein in grass carp culture wastewater reached up to 55.5% and 73.6% within one week, respectively. Moreover, in the acute toxicity test, when feed without LG37 was fed to grass carp, the safe concentration of ammonia nitrogen (non-ionic ammonium) was 3.37 mg/L (0.2 mg/L). When feed with LG37 was fed to grass carp, the safe concentration of ammonia nitrogen (non-ionic ammonium) was 5.11 mg/L (0.31 mg/L). Compared to feed without LG37, the feed with LG37 increased the toxicity tolerance of grass carp to ammonia nitrogen (non-ionic ammonium) by 51.63% (55%).