Methylomonas and Methylocystis Are Among the Dominant Cultivable Methanotrophs from Tropical Wetlands in India, Along with the Cultivation of Members from Newly Described Methylocucumis and Methylolobus Genera: A First Report

Wetlands are the most important natural sources of methane. Studies on the distribution and diversity of methanotrophs, especially in tropical wetlands, are limited. The studies on wetland methanotrophs help bridge the gap in the literature for understanding the community structure of methanotrophs in tropical wetlands. Our present study documents the methanotroph diversity from various wetland habitats across Western India. Samples from various sites such as freshwater ponds, lake sediments, mangroves, and small wetlands in stone quarries around multiple wetland ecosystems in Western India were collected and enriched for methanotroph isolation. As obtaining entirely pure cultures of methanotrophs is a tedious task, consuming months or years of streaking and re-streaking, methanotroph mono-cultures (a single methanotroph culture with a small number of heterotrophs) were established could be characterized using pmoA sequencing. Twenty-six mono-cultures were established, belonging to the genera Methylomonas, Methylocystis, Methylosinus, Methylocaldum, Methylocucumis, Methylomagnum, and Methylolobus genera. Eight methanotroph strains were purified in pure cultures- two Methylomonas koyamae, two Methylosinus sporium strains, one Methylolobus aquaticus, two Methylosinus trichosporium, and one strain of Methylomonas sp., which shows a close similarity with Methylomonas aureus and is possibly a novel species. A maximum number of cultures belonged to the Methylomonas and Methylocystis genera. Methylomagnum, a Type Ib methanotroph native to rice fields, was isolated from a pond in Pune. New members of Methylocucumis oryzae and Methylolobus aquaticus, two novel genera and species first reported by our lab from India, were also isolated in this study. Methanotrophs were high in most freshwater samples; in contrast, mangroves showed a relatively low abundance. Additionally, the cultivation approach helped us obtain new methanotrophs from this previously unexplored habitat, which can be used for further biotechnological and environmental applications.