Aims: Arthropods guts, such as termite harbor diverse microorganisms including those that are capable of fixing atmospheric nitrogen (N2). Nitrogen-fixing bacteria can help termite to overcome their shortage of dietary N by providing fixed N2. Nitrogenase enzyme is responsible for this trait and encoded by nif genes which are highly conserved and are primarily used in the identification of N2-fixing microorganisms. Here, we characterized N2-fixing bacteria isolated from the hindguts of termite Coptotermes gestroi. Methodology and results: A total of 46 bacterial isolates were obtained after a primary screening based on their ability to grow on Burk’s media. Subsequently, the nifH gene from two of these isolates, namely S7 and S20, were successfully amplified and sequenced. Molecular phylogenetic analysis of 16S rRNA gene sequence revealed that isolate S7 is closely related to Ralstonia pickettii ATCC27511 (99.34% similarity, 1059 bp), whereas isolate S20 is closely related to Microbacterium sp. NCCP-451 (LC488936) (99.06% similarity, 948 bp). Besides that, the recA gene of isolate S7 is closely related to Ralstonia pickettii 12D (CP001644) (100% similarity, 442 bp) and the type strain of Ralstonia pickettii (ATCC 27511) (NZ KN050646) (98.97% similarity, 438 bp). Meanwhile, nifH gene of isolate S7 showed highest similarity to the uncultured bacterium NR1606 (AF035490) (99.93% similarity, 277 bp). Moreover, the nifH gene of isolate S20 is clearly separated from Azoarcus sp. and distantly related to Microbacterium sp. The incongruence between the partial 16S rRNA and nifH gene sequences could indicate the possibility of horizontal transfer of nif genes. Conclusion, significance and impact of study The phylogenetic incongruence between housekeeping genes (16S rRNA and RecA) and nifH gene in these bacteria provides new insight on potential horizontal gene transfer (HGT) activity taking place in bacterial communities particularly in the guts of arthropods. The finding of this study on potential HGT can also aid in the prediction of origins and evolution of gene transfer among bacteria.
Nitrogen Fixation ; Nitrogenase ; Isoptera

Fifteen Rhizobium spp. from nodules of 6 common pulses collected from 6 districts of Assam were studied for their infectivity, intrinsic antibiotic resistance, nitrogenase activity and effect of dual inoculation with two native Arbuscular Mycorrhizal Fungi viz. Glomus mosseae(GM) and Gigaspora gilmarie(GG). Out of the 15 isolates 9 were found nodulation positive and 6 of them(AR1, BR8, BR12, AR10, UR10 & GR21) were subjected to intrinsic antibiotic sensitivity test of which AR1 showed resistance against all the 9 test antibiotics. Isolates AR1 and GR21 showed the highest(4.25 mole, gm(-1)hour(-1)) and the lowest(1.05 mole, gm(-1)hour(-1)) nitrogenase activity respectively. In Most Probable Number count, the maximum Rhizobium population 5.8x10(5), was found in both Blackgram and Greengram variety of pulses. The maximum dry weight of nodules(3.14 g), dry weight of shoot(10.08 g), nitrogen content(7.68 mg, plant(-1)), chlorophyll content(1.89 mg, g(-1)), phosphorus content of shoot(6.17 mg, g(-1)) and yield(535.67 kg, Ha(-1)) were found when AR1 dually inoculated with GM in Blackgram.
Anti-Bacterial Agents ; Chlorophyll ; Drug Resistance, Microbial ; Fungi* ; Nitrogen ; Nitrogenase ; Phosphorus ; Rhizobium*