Screening of a high bioflocculant‐producing bacterial strain from an intensive fish pond and comparison of the bioflocculation effects with Rhodococcus erythropolis

A high bioflocculant‐producing bacterial strain BX‐13 isolated from an intensive fish pond by multiple subcultures and measured through primary screening and rescreening using kaolin. The strain BX‐13 was identified to belong to the same branch as Bacillus subtilis by morphological, physiological and biochemical, 16S rDNA gene sequencing, Blast homology search and multiple sequence alignments. The bioflocculation potential of BX‐13 and Rhodococcus erythropolis was compared, using water from the intensive pond where BX‐13 was isolated. The results showed the number of colonies in the BX‐13 treatment was higher than that of the R. erythropolis treatment from day 10 to the end of the experiment (p < 0.05). The numbers of both BX‐13 and R. erythropolis in the water body peaked on day 15, with 2.23 × 10⁷ cfu/L and 9.90 × 10⁶ cfu/L respectively. The bioflocculation volume (BFV) in water increased and then stabilized in both BX‐13 and R. erythropolis treatments. The BFV in BX‐13 peaked on day 25 (52.13 ml/L) and R. erythropolis peaked on day 30 (22.63 ml/L). At the end of the experiment, the BFV of the BX‐13 treatment was higher than the R. erythropolis treatment (p < 0.05). In conclusion, B. subtilis BX‐13 has a very strong flocculation effect, and merits further research into its application for water quality regulation in aquaculture systems.