Biochemical and molecular investigation of non-rhizobial endophytic bacteria as potential biofertilisers

This study was performed to isolate non-rhizobial endophytic bacteria from the root nodules of Glycine max (soybean), Vigna radiata (mung bean) and Vigna unguiculata (cowpea). The bacteria were characterized for plant growth promoting properties such as indole acetic acid production, phosphate and zinc solubilisation, nitrogen fixation and hydrogen cyanide production. Phylogenetic identification was performed using the Neighbour-Joining method on16S rRNA gene sequences. The impact of salt tolerant isolates on some properties of wheat cv. Chamran was evaluated by a completely randomised factorial design. Nine isolates having some characteristics related to plant growth promotion were identified as Staphylococcus hominis 7E, Streptomyces sp. 11E, Bacillus sp. 13E, Acinetobacter sp. 19E, from mung bean, Bacillus endophyticus 1E from cowpea, Staphylococcus hominis 9E, Bacillus endophyticus 14E, Brevundimonas sp. 16E and Kocuria sp. 26E from soybean nodules. Isolates 7E and 19E caused maximum growth inhibition of Fusarium on PDA plate. All isolates were able to grow at salinity levels of mixtures containing up to 400 mM of NaCl, CaCl₂ and MgCl₂, but their growth was inhibited by increasing salinity level. Only the growth of isolate 14E increased at three levels of salinity compared with control. Some isolates, i.e. 7E, 14E, 19E and 26E had higher colony diameter at 45 °C after 48 h of incubation compared to the growth at 30 and 40 °C. Inoculation of soil with isolate 1E and isolate 26E caused to ameliorate salinity stress in wheat and increased the weight of 1000-grains as compared with non-inoculated treatments.

Keywords: Endophyte; Legumes; Nodule; Plant growth; Salinity.