Activity and Identification of Culturable Methanotrophs from Mangrove Sediments, South East Coast of India

Abstract

Anthropogenic activities have escalated CH4 emissions, exacerbating global warming, yet specialized bacteria known as Methanotrophs play a key role in mitigating atmospheric CH4 levels by consuming 30-70% of emitted methane. This study focuses on exploring the culturable methanotrophic population within Muthukuda mangrove sediments, an unexplored reservoir of methanotrophic diversity. The sediment sample yielded a methanotrophic bacterial count of 1.5 x 103 CFU/g, leading to the selection of three unique bacterial morphotypes (NCT270, NCT271, and NCT272) for in-depth investigation. Optimal growth was observed at pH 8, with peak growth at 30°C, while extreme temperatures of 4°C and 40°C inhibited growth across all isolates. Salinity levels between 20 and 30 ppt supported optimal growth, with strains displaying tolerance to various stressors. Methane served as the sole carbon source for all experiments, with positive urease production noted after 7 days of incubation. Microscopic and biochemical analyses suggested the classification of strains NCT270, NCT271, and NCT272 within Group I methanotrophic genera: Methylomicrobium, Methyloscarcina, and Methylomonas, respectively. BLASTn analysis of 16S rRNA gene sequences shared high similarities with known methanotrophic species Methyloscarcina fibrate (ON834586) with 99.28%, Methylomicrobium album (ON834587) with 98.77% and Methylomonas methanica (ON834588) with 99.15%. The resulting insights enhance our understanding of culturable methanotrophic diversity and underscore its potential for environmental applications.