Isolation and Characterization of a N2-fixing Bacterium from Coral Reef-seagrass Ecosystem

Abstract:

A strain capable of growth at high rates under nitrogen fixation conditions was isolated from the root of the seagrass (Thalassia hemprichii), which appeared after the degradation of coral reefs in Sanya natural reserves. The bacterium was identified as Pantoea agglomerans, which was also called Enterobacter agglomerans, on the basis of its morphology, physiological and biochemical characteristics, and the sequence analysis of 16S rDNA and the nitrogenase structural gene nifH. It was identified as a gram-negative, smooth, low raised, straight-rodded bacterium, which formed translucent colony with diameter of about 1 mm on the solid agar medium. Compared with the standard strain of the species Pantoea agglomerans (ATCC27155TM), there were high similarity in the carbon sources utility, hydrolysis and the optimal growth temperature and salinity. It could use a series of hydrocarbons as carbon sources, such as D-glucose, L-arabinose, sucrose, raffinose, maltose, rhamnose, D-xylose, D-mannitol, cellobiose, micronesia disaccharide. The results of the arginine dihydrolase, phenylalanine deaminase, lysine decarboxylation, ornithine deaminase were negative. The optimal growth temperature, pH and salinity were 37°C, 8 and 25‰, respectively. It could also grow at 40°C and pH was 10 but could not grow at zero salinity. Phylogenetic analysis of the 16S rDNA gene sequences (EU841417) showed more than 99% similarities to that from other recognized Pantoea agglomerans. The nitrogen fixation rate of G33-1 was 299.16 nmol C2H2/(mL·h).