Distribution of baroduric, psychrotrophic and culturable nitrifying and denitrifying bacteria in the Central Indian Basin

Abstract

The abundance of baroduric, culturable nitrifying and denitrifying bacteria in the deep-sea cores of Central Indian Basin (CIB) at ca 5000 m depth was investigated. Analysis of 8 cores, sampled between 10 degrees 00 minutes S and 75 degrees 55 minutes-76 degrees 05 minutes E, showed that nitrifying bacteria were present in layers of sediment 0-25 cm below sea floor (bsf) with maximum numbers at sub-surface layers. Their average numbers ranged from 4.0 x 10 sup(4) to 2.43 x 10 sup(8) CFU g sup(-1) dry weight sediment and formed 0.21 and 4.30% of the total counts. Unusually high number of nitrifiers comprising of 40% of the total bacterial population have been encountered in one of the cores, namely CIB 16. Denitrifying bacterial population ranged from 0.02 to 2.57 x 10 sup(2) CFU g sup(-1) dry weight sediment and remained restricted to the surface sediment 0-4 bsf). The availability of organic carbon was found to be an important factor regulating the distribution of denitrifying and nitrifying bacteria in the sediment layers of CIB. While nitrifiers are negatively controlled by the organic matter, denitrifiers are positively controlled. Thus the widespread occurrence of nitrifying ability could be responsible for making oxygenated waters of the deep oceans including CIB net nitrifying and therefore rich in nitrate.