Diverse Type I and Type II methanotrophs cultivated from an Indian freshwater wetland habitat

Abstract

Abstract Wetlands are the largest natural sources of microbial methane and contribute to approximately 23% of the global methane. Such wetland patches serve as rich habitats for aerobic methanotrophs. Limited knowledge of methanotrophs from tropical wetlands widens the scope of study from these habitats. In the present study, a freshwater wetland from a tropical region in India was sampled serially diluted to obtain methanotrophs in culture. This was followed by isolation on agarose-containing plates, incubated under a methane: air atmosphere. Methanotrophs are difficult to cultivate, and a very few cultures of methanotrophs are available from tropical wetlands. In our present study, we could culture a diverse community of methanotrophs from six genera, namely, Methylomonas, Methylococcus, Methylomagnum, Methylocucumis (Type I methanotrophs), and Methylocystis, Methylosinus (Type II methanotrophs). A strain of the newly described methanotroph, Methylocucmis oryzae, for which only two strains have been documented worldwide, was also successfully cultured in the study. A high abundance of methanotrophs (106-1010 methanotrophs/g fresh weight) was observed in the samples. A Methylococcus strain representing a putative novel species was also isolated. A large number of Methylomonas strains were cultured, all related to Methylomonas koyamae. Our study is one of the first documentation of culturable methanotrophs from a tropical wetland and reports that such wetland patches may contain high counts and diversity of methanotrophs. The isolated methanotrophs can act as models for studying methanotroph-based methane mitigation from wetland habitats and can be used for various mitigation and valorization applications.