Characterization and Strain Improvement of Aerobic Denitrifying EPS Producing Bacterium Bacillus cereus PB88 for Shrimp Water Quality Management

A bacterial strain PB88 was isolated from intensive shrimp culture pond to study the denitrification process. On the basis of 16S rDNA analysis, strain PB88 was identified as Bacillus cereus PB88. It has the potential to remove 82.33 +/- 3.24% NO2--Nin synthetic medium. The optimum pH, temperature and dissolved oxygen for the highest denitrification process of the PB88 were 8.0, 30 degrees C and 5.21 mg/l (150 rpm) respectively. PB88 harbour the genetic sequence of nitrite reductase (nirS) enzyme which is essential to complete aerobic denitrification process. One remarkable finding is that the experimental organism produced exopolysaccharide (EPS) during the denitrification process and EPS has the antibacterial property against shrimp pathogen Vibrio harveyi MTCC 7954 (inhibition zone of 5.21 mm) and Vi brio vulnificus MTCC 1145 (inhibition zone of 7.11 mm). Removal of NO2--N in open base shrimp wastewater system were recorded as 98.51% by B. cereus PB88 and average shrimp body weight gained in treated system as 6 +/- 0.54 to 8 +/- 0.74 g within 7 days. Overall result indicated that B. cereus PB88 has the immense potential for the application in commercial shrimp culture as denitrifying agent.