Studies on N2-fixing bacteria associated with the salt-tolerant grass,Leptochloa fusca (L.) Kunth

Abstract

N2-fixing bacteria were isolated from the rhizosphere of naturally grown salt tolerant grass (Leptochloa fusca). A broad spectrum of diazotrophs was found to be associated with the roots ofL. fusca. the systematic position of the three isolates, NIAB-1, C-2 and Iso-2 was determined by morphological, biochemical and mol % (G+C) DNA contents. Two isolates were identified asKlebsiella pneumoniae (NIAB-1) andBeijerinckia sp. (Iso-2).15N enrichment studies confirmed the nitrogen fixing ability of the isolates. The effects of different levels of combined nitrogen (NO −3 & NH +4), pH (5.5–9.0) and salt (NaCl) on nitrogenase activity of the isolates were determined at various time intervals. All isolates exhibited nitrogenase activity even in the presence of 5 mmol/l NO −3 or NH +4 in a semi-solid medium after 24 h of growth. Maximum nitrogenase activity was observed at alkaline pH and all isolates were able to tolerate up to 3% NaCl in the medium