Methane utilizing plant growth-promoting microbial diversity analysis of flooded paddy ecosystem of India

Abstract

Methane utilizing bacteria (MUB) are known to inhabit the fooded paddy ecosystem where they play an important role in regulating net methane (CH4) emission. We hypothesize that efcient MUB having plant growth-promoting (PGP) attributes can be used for developing novel bio-inoculant for fooded paddy ecosystem which might not only reduce methane emission but also assist in improving the plant growth parameters. Hence, soil and plant samples were collected from the phyllosphere, rhizosphere, and non-rhizosphere of fve rice-growing regions of India at the tillering stage and investigated for efcient methane-oxidizing and PGP bacteria. Based on the monooxygenase activity and percent methane utilization on NMS medium with methane as the sole C source, 123 isolates were identifed and grouped phylogenetically into 13 bacteria and 2 yeast genera. Among diferent regions, a signifcantly higher number of isolates were obtained from lowland fooded paddy ecosystems of Aduthurai (33.33%) followed by Ernakulum (20.33%) and Brahmaputra valley (19.51%) as compared to upland irrigated regions of Gaya (17.07%) and Varanasi (8.94%). Among sub-samples, a signifcantly higher number of isolates were found inhabiting the phyllosphere (58.54%) followed by non-rhizosphere (25.20%) and rhizosphere (15.45%). Signifcantly higher utilization of methane and PGP attributes were observed in 30 isolates belonging to genera Hyphomicrobium, Burkholderia, Methylobacterium, Paenibacillus, Pseudomonas, Rahnella, and Meyerozyma. M. oryzae MNL7 showed signifcantly better growth with 74.33% of CH4 utilization at the rate of 302.9±5.58 and exhibited half-maximal growth rate, Ks of 1.92±0.092 mg CH4 L−1. Besides the ability to utilize CH4, P. polymyxa MaAL70 possessed PGP attributes such as solubilization of P, K, and Zn, fxation of atmospheric N and production of indole acetic acid (IAA). Both these promising isolates can be explored in the future for developing novel biofertilizers for fooded paddies.