Isolation of elite diazotrophic bacterial isolates from Cyanodon dactylon rhizosphere of saline soils

In the present study, out of sixty rhizosphere diazotrophic isolates, twenty seven isolates from rhizosphere recorded positive in N-free medium. Isolates showing growth in N-free medium were subjected to ammonia production and total nitrogen concentration measurement. Among the diazotrophic isolates CD6 and CD12 were found to produce the maximum amount (14.90 +/- 0.12 mg N g(-1) of malate) of nitrogen and ammonia (4.3+/-0.26 mg ml(-1)) respectively. The nitrogenase enzyme activity of the isolates ranged from 45.29 +/-0.03 to 174.25 +/-0.89 n moles of ethylene mg(-1) of protein h(-1). The highest nitrogenase activity was exhibited by isolate CD6 (174.25 +/-0.89 n moles of ethylene mg(-1) of protein h(-1)). The maximum amount of IAA and GA was produced by CD6 (26.7 +/-0.25 mu g g(-1) protein and CD20 (23.7 mu g g(-1) protein) respectively. In the present study the capability of the 8 isolates to solubilize insoluble forms of phosphorus and zinc were tested. Among the dizotrophic isolates, the isolate CD20 recorded the maximum production of siderophore and HCN (60.61 mu g mg(-1) dry weight of cell of catechol type and 61.8+/-1.18. g ml(-1)) respectively. The antagonistic activity of all the diazotrophic isolates against 2 rice pathogenic organism viz., sheath rot (R. solani) and blast (P. oryzae) was evaluated and 7 isolates were effective against 2 selected pathogens. The pot culture experiment results revealed that there was a significant increase in biomass, shoot length, root length, nitrogen content of diazotrophic isolates when compared with uninoculted control. Out of eight isolates tested in the present investigation, two efficient isolates viz., CR6 and CR20 were selected for 16 srRNA sequencing, isolates belong to Serratia sp and Klebsiella pneumoniae within the order Enterobateriales.