The first cultures of India's indigenous natural methane mitigating agents reported from rice fields and wetlands, mainly from western India, may help to tackle the upcoming climate challenges. While the world is facing global warming and climate change, there are some hardworking microbes in this world, which are doing their job to reduce the ill-effects of global warming. Methane, the second most important greenhouse gas, has 26 times more global warming potential than carbon-di-oxide. Wetlands, ruminant animals, paddy fields, landfills are the sources of methane produced by the action of methanogens.
In a countervailing manner, methanotrophs or methane oxidizing bacteria oxidize this methane and take in oxygen while building up their biomass and producing carbon dioxide (CO2) and water (H2O) just like us. Methanotrophs are natural methane mitigating agents and are present in all environments where both methane and oxygen are available. Wetlands, paddy fields, ponds and other water bodies are the habitats where they grow in abundance. It is due to the activities of methanotrophs that atmospheric methane values have not increased unexpectedly in the last few years. Dr. Monali Rahalkar, scientist at MACS Agharkar Research Institute, an autonomous institute of the Department of Science and Technology, along with her team has isolated and characterized India’s first culture variant of indigenous methanotrophs from paddy fields and wetlands, primarily from Western India.
Isolating methanotrophs from India, he published the first unique methanotroph description from India and a new genus and species- Methylocuccumis oryzae. The specialty of this methanotroph was that it had a distinctive oval and elongated shape similar to cucumber, and hence this unique genus was named 'Methane Eating Cucumbers'. His team could culture another similar organism from a rice field in subsequent years despite the isolation of this particular methanotroph. Recently Methylocuccumis oryzae was found as an important methanotroph component of a stone quarry in Pune, located amidst the popular hill, Vetal Tekdi or Arai hill.
The hill has its own unique flora and fauna including rock quarry waters with unique invertebrates and molluscs. Dr. Rahalkar's team recently documented the abundance of methanotrophs in the water-filled quarry, indicating that an active methane cycle operates in this unique habitat. After nearly 6 years of description and nearly 10 years of isolation of its first member, Methylocuccumis oryzae remains phylogenetically unique. No such strain has been reported or cultured from any other country or part of the world. Its size is remarkably large compared to other bacteria and is comparable to the size of a small yeast (3-6 µm). Another unique feature of this bacterium is its strict mesophilic nature and cannot tolerate temperatures above 37 °C, whereas most other methanotrophs can tolerate 37 °C or even 40 °C and grow well.
The bacterium forms pale pink colonies, and the genome is indicative of the carotenoid pathway. In recent years, this methanotroph has also been found to promote growth of rice plants by promoting early ear formation and increasing grain yield. The methanotroph was added to transplanted rice plants in pot experiments using the locally popular high-yielding rice variety Indrayani. Current constraints with Methylocuccumis are slow growth which prevents the culture from growing at the scale needed for mitigation and biotechnology applications. Nevertheless, there is evidence that this organism exists in abundance in nature in wetlands and paddy fields and can perform its function discreetly.
This information about the unique methanotroph Methylocuccumis oryzae was recently published in the Indian Journal of Microbiology. Earlier reports on three strains of this methanotroph and its genome have been published in Microbial Ecology, Antonie van Leeuwenhoek, Frontiers in Microbiology and International Microbiology. The discovery of such a unique and possibly endemic methanotroph is significant for further study of this important group in relation to upcoming climate challenges. Further improvement in culture conditions as well as large-scale cultivation may help in more applications of this organism.