Isolation, Culture, and Identification of Two Strains of Probiotics and Their Effects on Water Quality Control

Abstract:

Good water quality is essential for the healthy growth of pond-cultured marine fish. Balanced microecological environment plays an important role in the maintenance of water quality and control of fish disease. To identify the mechanisms regulating the balance in microecological environment and to find specific and high-efficiency probiotics for pond culture of marine fish, here we tested two strains of bacteria isolated from sewage sludge of the estuary area of the Futuan River in Rizhao. They were identified as Lactobacillus plantarum and a Bacillus subtilis-like species according to the analysis such as morphological characteristics, biochemical properties, and 16S rRNA sequencing. The optimum growth conditions for L. plantarum and B. subtilis were pH 6.5/temperature 30℃ and pH 6.0/temperature 36℃ respectively. In the laboratory, the degrading effects of the mixed bacteria strains A and B (1:1) on ammonia nitrogen, nitrite, and phosphate in the seawater were 73.2%, 58.0%, and 52.4% respectively. Next, we examined the degrading effects of the bacteria in two outdoor marine ponds rearing Japanese flounder. One was designated as the experimental pond added with the probiotics (mixture of strain A and strain B), and the other one was the control. The applications of the probiotics (1:1, bacteria density 5×104–10×104 cell/ml) caused significant decrease in the concentrations of ammonia nitrogen, nitrite, and phosphate, and the degrading rates were 86.3%, 88.9%, and 68.3% respectively. Our results provided useful information for large-scale production of the two probiotics and for their application in aquaculture in the future.