[Isolation, identification and fermentation optimization of lactic acid bacteria for aquaculture water purification].

Objective: In order to get excellent strains for aquiculture water purification, we screened lactic acid bacteria from the aquaculture environment and intestinal tract of shrimp.

Methods: The potential water purification ability of lactic acid bacteria at normal and low temperature was evaluated in the simulated wastewater. Morphological physio-biochemical characteristics, 16S rRNA gene sequence analysis were used to identify strain r13. Single factor test and orthogonal-design experiment were applied to optimize fermentation for r13.

Results: In total 136 lactic acid bacteria strains were isolated from 3 samples. The results of water purification test suggested r13 had higher removal ability of nitrite and ammonia from water. After 72 h treatment by r13, nitrite with 11.5 mg/L in the water was completely removed and ammonia degradation rate was 29.1% with 13.0 mg/L original concentration. According to morphological, physio-biochemical characteristics and 16S rRNA gene sequence analysis, r13 was identified as Lactobacillus plantarum. The optimal fermentation condition for r13 was 6.0 g/L yeast extract, 20.0 g/L glucose, 4.0 g/L sodium acetate, 2.0 g/L diammonium hydrogen citrate, 2.0 g/L monopotassium phosphate, 50 mL tomato juice, with inoculation rate 5% (V/V), at pH 6.0 and 34℃. Under this condition cultured for 72 h, the bacterial biomass reached 28.4 g/L wet weight and cell counting reached 4.4×109 CFU/mL.

Conclusion: Considering high nitrite removal ability, we suggested that r13 would be promising microorganism for water purification in aquiculture.