Divulging diazotrophic bacterial community structure in Kuwait desert ecosystems and their N2-fixation potential

Kuwait is a semi-arid region with harsh climatic conditions with poor available soil nutrient essential for the growth of plants. Kuwaits ecosystem is relatively N-poor ecosystem when compared to the other ecosystems. Biological nitrogen fixation (BNF) is a spontaneous process in which diazotrophic bacteria fixes the atmospheric nitrogen directly in to the bionetwork. At present, there is limited information on free-living and root associated nitrogen-fixing bacteria, their potential to fix nitrogen to aid natural plant communities in the desert of Kuwait. In this study, free-living N2-fixing bacteria were enriched and isolated from the rhizospheric soil of three keystone native plant species of Kuwait; such as Rhanterium epapposum, Farsetia aegyptia, and Haloxylon salicornicum. Root associated bacteria were directly isolated from the root nodules of Vachellia pachyceras. In this study, a number of free-living and root associated dizotrophs were isolated from various rhizospheric soils of three native shrubs and root nodules from one tree species. The screened isolates were assessed for nitrogen-fixing ability and identified using Acetylene Reduction Assay (ARA) and 16s rRNA gene sequencing, respectively. Our study successfully identified all the 50 nitrogen-fixers isolated initially and out of that, 78% were confirmed as nitrogen-fixers using ARA. Among the identified nitrogen fixers, the genus Rhizobium is dominant in rhizospheric soil of Rhanterium epapposum, whereas Pseudomonas and Rhizobium are dominant in the rhizospheric soil of Farsetia aegyptia, and Haloxylon salicornicum respectively. The species Agrobacterium tumefaciens is found dominant in the root nodules of V. pachyceras. The current results indicate that plant species and their rhizospheric effects are important drivers for specificity of microbial diversity in arid soils. To our knowledge, this study is the first investigation of culture-based isolation, molecular identification, and evaluation of N2-fixing ability of diazotrophs from Kuwait desert environment.