Analysis of nhaA gene from salt tolerant and plant growth promoting Enterobacter ludwigii

Salt tolerant plant growth promoting rhizobacteria (PGPR) can reduce the impact of salinity on plant growth and its productivity. The present study was conducted on salt tolerant (upto 2.6 M sodium chloride) plant growth promoting Enterobacter ludwigii and its Na+/H+ antiporter gene. This isolate was obtained from the rhizospheric soil of Cynodon dactylon growing around the salt mines of Himachal Pradesh (India) and identified on the basis of morphology, biochemical and 16S rRNA typing techniques. Various plant growth promoting traits of this bacterium viz., nitrogenase activity, siderophores production, Indole acetic acid production, proteolytic activity and tricalcium phosphate solubilization were analysed under salt stress (0.86 M NaCl) conditions. Effect of E. ludwigii inoculation on the growth and quality of tall fescue (Festuca arundinacea) under salt stress conditions (0.17 M to 0.86 M NaCl) was also studied. It was observed that saline soil significantly reduced the tall fescue growth, whereas, inoculation with bacterium resulted in significant augmentation in growth and quality of this grass. This isolate E. ludwigii seems to be a good bioinoculant for crops in normal and salt affected soils. The allele mining of nhaA gene conferring the salt tolerance behaviour on many prokaryotes, was carried out and the gene sequence was compared with lineages of China, Israel, UK and USA available in the literature. The phylogenetic tree obtained from the mining of nhaA showed little variation in gene sequences of this bacterium in comparison to the above referred lineages. The deduced NhaA protein (Na+/H+ antiporter) of E. ludwigii contained 384 amino acids and its secondary structure revealed that NhaA had 44.85% a-helices, 12.11% beta-turns, 22.94% extended strands and 20.10% random coils. The sequence homology of this strain with nhaA of E. coli and its putative 3D structure suggested its role in salt tolerance mechanism.