Assessment of phosphorus mobilizing capacity of Bacillus spp. isolated from mangrove rhizospheric sediment and its potential application in aquaculture

Phosphatase producing bacteria (PPB) plays a major role in mineralising organic P into inorganic form. Though application of bacterial biofertilizers are practiced in agriculture, their application is very limited in aquaculture.

The PPB isolates were screened and isolated from rhizospheric sediment of mangrove, Avicennia marina of Ennore creek, Tamil Nadu. Their P transformation potential and the possibilities of their application in aquaculture to mineralise organic P to inorganic P were studied.

Twenty PPB isolates were screened in the study site and their Alkaline Phosphatase (ALP) activity was in the range of 13.6-20.4 μmol.ml^-1.hr^-1. Out of this, five Bacillus sp isolates were selected to assess their P transformation potential at various salinity. The P mobilizing potential of these isolates were compared with the commercial PPB following a microcosm study for a period of 14 days. During the study period, there is a significant increase in phosphorus in water as well as ALP activity and available phosphorus concentrations in sediments were observed between control and treatment tanks. Among the treatment groups, B. subtilis treatment tanks showed maximum P in water i.e. 1.60 mg.L^-1, followed by B. altitudinis -1.49 mg.L^-1; B. pumilus -1.47 mg.L^-1; the soil ALP activity was in the order of commercial P products > B. pumilus > B. subtilis > B. paramycoides > B. altitudinis > B. aryabhattai. In terms of available phosphorus content in sediments on 14^th day, there is no significant difference observed between B. pumilus and commercial product with respect to available P content of sediment.