Occurrence of effective nitrogen-scavenging bacteria in the rhizosphere of kallar grass

Bacteria occurring in high numbers on the rhizoplane of kallar grass grown at a natural site in Pakistan were effective scavengers of traces of combined nitrogen from the atmosphere. Bacteria grew under appropriate conditions in nitrogen-free semi-solid malate medium in the form of a typical subsurface pellicle which resulted in a significant nitrogen gain in the medium within 3 to 4 days of incubation; this could be also measured by¹⁵N-dilution. Bacteria grew and incorporated nitrogen under an atmosphere containing NH₃ and N₂O. A rapid and strong binding of strain W1 to roots of kallar grass grown in hydroponic culture was found by using a³²P-tracer technique. We obtained no evidence for diazotrophy of our strains because they failed to grow on nitrogen-free media when gases of high purity were used. No¹⁵N₂ was incorporated when bacteria were grown on¹⁵N₂ although a nitrogen gain was found, no acetylene reduction was observed and no homology with DNA containing sequences ofnifHDK structural genes for the nitrogenase components fromKlebsiella pneumoniae were detected. Owing to close contact of these bacteria with roots of kallar grass, utilization of scavenged nitrogen by the plant may have to be taken into account.