A dearth of information is available for nitrogen-fixing bacteria in coastal mangroves, and
hence, the present study has been undertaken to analyse 44 root and associated soil samples,
derived from a mangrove habitat of southeast coast of India. The root samples exhibit high
counts of total heterotrophic bacteria and azotobacters along with high rates of nitrogen fixation,
as compared to the rhizosphere soil samples. Among the plant species, Bruguiera cylindrica
records high microbial counts and nitrogen fixation. From the samples analysed, three species of
Azotobacter, viz., A. chroococcum, A. virelandii and A. beijerinckii were isolated, purified and
identified. These species exhibit high growth, nitrogen fixation and in vitro production of
phytohormone (Indole Acetic Acid, IAA) at NaCl salinity of 30 g l 1. The azotobacters, which
were inoculated with Rhizophora seedlings, increased significantly the average root biomass up
to by 98.2%, the root length by 48.45%, the leaf area by 277.86%, the shoot biomass by 29.49%
as compared to controls and they also increased the levels of total chlorophylls and carotenoids
up to by 151.0% and 158.73%, respectively. Thus, azotobacterisation is beneficial in raising
vigorous seedlings of mangroves in coastal wetlands.