A metagenomic study of methanotrophic microorganisms in Coal Oil Point seep sediments

Blast searches followed by taxonomic binning in MEGAN revealed aerobic methanotrophs of the genus Methylococcus to be overrepresented in the 0-4 cm metagenome compared to the 10-15 cm metagenome. In the 10-15 cm metagenome, ANME of the ANME-1 clade, were identified as the most abundant methanotrophic taxon with 8.6% of the reads. Searches for particulate methane monooxygenase (pmoA) and methyl-coenzyme M reductase (mcrA), marker genes for aerobic and anaerobic oxidation of methane respectively, identified pmoA in the 0-4 cm metagenome as Methylococcaceae related. The mcrA reads from the 10-15 cm horizon were all classified as originating from the ANME-1 clade.Most of the taxa detected were present in both metagenomes and differences in community structure and corresponding metabolic potential between the two samples were mainly due to abundance differences.The results suggests that the Tonya Seep sediment is a robust methane filter, where taxa presently dominating this process could be replaced by less abundant methanotrophic taxa in case of changed environmental conditions.The Coal Oil Point seep area (COP), located in the Santa Barbara Channel, California, is one of the most active seep areas in the world [1]. Seepage of the greenhouse gas methane and other hydrocarbons has occurred in this area for over 500 000 years [2]. The methane emitted from the COP is mainly of thermogenic origin and the daily emission has been estimated to be at least 40 metric tons [1,3].At a global scale, the oceans only make up about 2% of the global methane emission budget [4]. This low level is explained by prokaryotic oxidation of methane in marine sediments and bedrocks before it reaches the water column [5].The oxygen penetration level in marine sediments is shallow, so most of the methane oxidation takes place at anaerobic conditions. Anaerobic oxidation of methane (AOM) is assumed to be a coupling of reversed methanogenesis and sulphate reduction. This process is likely performed