Abstract
Methanotrophs are aerobic to micro-aerophilic bacteria, which oxidize and utilize methane, the second most important greenhouse gas. The community structure of the methanotrophs in rice fields worldwide has been studied mainly using culture-independent methods. Very few studies have focused on culturing methanotrophs from rice fields. We developed a unique method for the cultivation of methanotrophs from rice field samples. Here, we used a modified dilute nitrate mineral salts (dNMS) medium, with two cycles of dilution till extinction series cultivation with prolonged incubation time, and used agarose in the solid medium. The cultivation approach resulted in the isolation of methanotrophs from seven genera from the three major groups: Type Ia (Methylomonas, Methylomicrobium, and Methylocucumis), Type Ib (Methylocaldum and Methylomagnum), and Type II (Methylocystis and Methylosinus). Growth was obtained till 10–6–10–8 dilutions in the first dilution series, indicating the culturing of dominant methanotrophs. Our study was supported by 16S rRNA gene-based next-generation sequencing (NGS) of three of the rice samples. Our analyses and comparison with the global scenario suggested that the cultured members represented the major detected taxa. Strain RS1, representing a putative novel species of Methylomicrobium, was cultured; and the draft genome sequence was obtained. Genome analysis indicated that RS1 represented a new putative Methylomicrobium species. Methylomicrobium has been detected globally in rice fields as a dominant genus, although no Methylomicrobium strains have been isolated from rice fields worldwide. Ours is one of the first extensive studies on cultured methanotrophs from Indian rice fields focusing on the tropical region, and a unique method was developed. A total of 29 strains were obtained, which could be used as models for studying methane mitigation from rice fields and for environmental and biotechnological applications.
Highlights
IntroductionAerobic methanotrophs use methane gas as their sole source of carbon and energy source (Hanson and Hanson, 1996)
Methane is the second most important greenhouse gas after carbon dioxide
A two-step dilution till extinction enrichment process was used for the cultivation of methanotrophs, where we used serum bottles for the first step followed by serial dilution of each of the positive enrichment in microtiter plates in eight steps (Figure 1)
Summary
Aerobic methanotrophs use methane gas as their sole source of carbon and energy source (Hanson and Hanson, 1996). Most of the described and available methanotrophs belong to the phylum Proteobacteria. Methanotrophs inhabit rice fields (Frenzel, 2012), lakes (Pester et al, 2004; Rahalkar, 2007; Oswald et al, 2016), wetlands (Dedysh, 2009), soda lakes (Antony et al, 2012), compost (Kim et al, 2008), forest soils (Dunfield et al, 2003), peat bogs (Pytlak et al, 2012), thermal springs (Hirayama et al, 2011), and marine sediments (Bowman et al, 1997; Tavormina et al, 2015)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
