Effect of Salinity on the Growth and Nitrogen Fixation of Azotobacter Beijerinckii

Abstract

The influence of salinity on Lhe growth and nitrogen fixation capacity of Azotobacter beijerinckii in prawn-cum-paddy culture system is discussed in the present paper. Thirty nitrogen fixing Azotobacter strains isolated from brackishwater shrimp ponds identified into three species viz., Azotobacter chroococcum, A. virtelandii and A. beijerinckii. The study on eight strains of A. beijerinckii reveals that the salinity levels above 30-35 %o and below 5 %a, in general, result in their reduced growth. In most of the strains maximum nitrogen fixation occured at 30-35 %o. Nitrogen fixation was relatively inactive with little variations among most of the strains growing in salinity <20 %o as well as >50 %o. The strains of A. beijerinckii required salinity levels ranging from 30 to 35 %o for optimal growth and nitrogen fixation.