Description of novel marine bioflocculant-producing bacteria isolated from biofloc of pacific whiteleg shrimp, Litopenaeus vannamei culture ponds

Description of marine bioflocculant-producing bacteria isolated from biofloc of Pacific whiteleg shrimp, Litopenaeus vannamei culture ponds was prompted to explore the bacteria that enhanced bioflocculation process in aquaculture wastewater treatment. Certain marine bacteria were potentially secreted extracellular polymeric substances (EPS) which response to the physiological stress encountered in the natural environment that can act as bioflocculants. This study aimed to identify marine bioflocculant-producing bacteria isolated from biofloc; to evaluate their flocculating activities; and to characterize their protein in EPS. Phenotypic and genotypic identification of the bacteria including morphological and molecular approaches were employed, while their flocculating activities were examined via Kaolin clay suspension method and statistically analyzed. The EPS that acted as bioflocculants were extracted using cold ethanol precipitation method. Protein concentration was determined by Bradford assay and protein profiling was finally completed with Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) method. Six species of marine bacteria known as Halomonas venusta, Bacillus cereus, Bacillus subtilis, Bacillus pumilus, Nitratireductor aquimarinus and Pseudoalteromonas sp. were successfully identified as bioflocculant-producing bacteria. The highest flocculating activity was exhibited by Bacillus cereus at 93%, while Halomonas venusta showed the lowest record at 59%. All bioflocculant-producing bacteria species showed different protein concentration that ranged between 1.377 g/mL to 1.455 g/mL. Several protein bands with different molecular weight that ranged between 16 kDa to 100 kDa were observed. This study revealed that all the identified bacteria species have high potential characteristics to initiate aquaculture wastewater treatment and may play important roles in bioflocculation process.\n\nImportanceSix species of marine bacteria isolated from biofloc of Pacific whiteleg shrimp, Litopenaeus vannamei culture ponds were identified as bioflocculant-producing bacteria. Among those six species, Bacillus cereus, Bacillus pumilus, Nitratireductor aquimarinus and Pseudoalteromonas sp. were highly potential to be used as booster for rapid formation of biofloc due to their high flocculating activities. Protein content in EPS of novel marine biofocculant-producing bacteria has beneficial consequences on degradation process of organic substances, denitrification of wastes and ions elimination from aquaculture wastes.