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Bioprospecting of Microbial Diversity for Sustainable Agriculture and Environment
Published in Vineet Kumar, Vinod Kumar Garg, Sunil Kumar, Jayanta Kumar Biswas, Omics for Environmental Engineering and Microbiology Systems, 2023
Hiren K. Patel, Nensi K. Thumar, Priyank D. Patel, Azaruddin V. Gohil
Generally, at the phyla scale, Archaea, Cyanobacteria, Firmicutes, and Proteobacteria are associated with nitrogen fixation in soil. Azospirillum, which is microaerophilic, and Herbaspirillum are found to be specific to rhizosphere and help in nitrogen fixation (Rashid et al 2016). Symbiotic nitrogen-fixing rhizobacteria include Azoarcus sp., Beijerinckia sp., Klebsiella pneumoniae, and Rhizobium sp. (Ahemad and Kibret 2014). Other bacterial species involved in nitrogen fixation are Azotobacter chroococcum, Bacillus megaterium, B. mucilaginosus, Bradyrhizobium japonicum UCM B-6018, Burkholderia sp., Pantoea agglomerans, Pseudomonas aeruginosa BS8, P. alcaligenes PsA15, P. fluorescens C7, and Rhizobium leguminosarum (Rashid et al 2016). Rhizobium leguminosarum is a symbiotic mutualistic bacterium that fixes nitrogen with nodule formation. Strains of Rhizobium leguminosarum have many plasmids that are host specific, and only one plasmid from each strain is involved in symbiosis through expression of nod, sym, and fix genes. Plasmid transfer can improve symbiotic nitrogen fixation (Kalloo 1993). Azotobacter chroococcum produce melanin during metabolism, which helps in the protection of nitrogenase enzyme from oxygen (Shivprasad and Page 1989). The fungi that are reported to be indirectly involved in nitrogen fixation are Claroideoglomus claroideum, C. etunicatum, Glomus mosseae, G. viscosum, and Rhizophagus intraradices. Glomus viscosum is arbuscular mycorrhizal symbiotic fungi that take part in the improvement of nutrient uptake and provide protection against drought stress to crops (Bidartondo et al. 2002). Fungi in the soil directly do not fix environmental nitrogen, but they provide nutrients to bacteria that are involved in nitrogen fixation. Mycelium of fungi also provides protection of bacterial enzymes against oxygen for successful nitrogen fixation. In symbiotic association of fungi and bacteria, fungi provide carbon and phosphorous to bacteria for growth. Arbuscular fungi also enhance the growth of non-symbiotic nitrogen fixer bacteria by supplementation of carbon (Jones and Oburger 2011). Both symbiotic and non-symbiotic microbes can be used for nitrogen replenishment in nutrient-deprived agricultural soil for plant growth.
Nickel tolerance and biosorption potential of rhizobia associated with horse gram [Macrotyloma uniflorum (Lam.) Verdc.]
Published in International Journal of Phytoremediation, 2021
Prabhavati Edulamudi, Anthony Johnson Antony Masilamani, Umamaheswara Rao Vanga, Venkata Ramana Sai Gopal Divi, Veera Mallaiah Konada
The rhizobial isolates were more sensitive to Ni (Pereira et al.2006). Ni at 10 µg mL−1 concentration has shown lethal effect on R. leguminosarum bv. trifolii strains (Milicic et al.2006). At 1 µg mL−1, Ni stimulated the growth of cowpea Bradyrhizobium when inoculated in YEM medium (Singh and Rao 1997). Rhizobium and Sinorhizobium isolates obtained from various industrial areas of Navi Mumbai have shown tolerance to Ni. The strain BEL5B has shown tolerance to Ni at 3 mM (Jobby et al.2015). Bradyrhizobium strains, isolated from Serianthes calycina growing in Ni-rich soils and rhizobia from Mimosa pudica were able to grow in the presence of Ni at 15 mM (Chaintreuil et al.2007; Klonowska et al.2012). Rhizobium leguminosarum biovar trifolii has shown tolerance to 0.24 to 0.26 mM Ni2+ (Purchase and Miles 2001). The Ni-tolerant Rhizobium strains RP5 and RL9 were isolated from nodules of pea and lentil, grown in metal-polluted farms have shown high tolerance to Ni at 350 and 500 µg mL−1 (Wani et al.2008; Wani and Khan 2013). Bradyrhizobium strain RM8 from green gram and Rhizobium sp. RP5 isolated from pea nodules were also tolerant to Ni (Wani et al.2007, 2008). Rhizobium strains (L9 and L19) have shown higher tolerance than Mesorhizobium (L42 and L50) to Ni at lowest dose (0.2 mM; Marzena et al.2020). Bradyrhizobium (Wani et al. 2007), R. leguminosarum (Rubio et al.1994), and Mesorhizobium strains isolated from nodules of legume plants growing on Ni contaminated soils have shown metal tolerance (Porter and Rice 2013). Mesorhizobium bacteria have active Ni efflux systems to prevent toxic intracellular Ni concentrations (Maynaud et al.2013). Hence, this is the first report on rhizobia associated with horse gram to tolerate up to 1,000 µg g−1 of Ni concentration.