We have previously identified a sulfate methane transition
zone (SMTZ) within the methane hydrate-bearing sediment
in the Ulleung Basin, East Sea of Korea, and the presence of
ANME-1b group in the sediment has been shown by phylogenetic
analysis of a 16S rRNA gene. Herein, we describe
taxonomic and functional profiling in the SMTZ sample by
metagenomic analysis, comparing with that of surface sediment.
Metagenomic sequences of 115 Mbp and 252 Mbp
were obtained from SMTZ and surface sediments, respectively.
The taxonomic profiling using BLASTX against the
SEED within MG-RAST showed the prevalence of methanogens
(19.1%), such as Methanosarcinales (12.0%) and
Methanomicrobiales (4.1%) predominated within the SMTZ
metagenome. A number of 185,200 SMTZ reads (38.9%) and
438,484 surface reads (62.5%) were assigned to functional
categories, and methanogenesis-related reads were statistically
significantly overrepresented in the SMTZ metagenome.
However, the mapping analysis of metagenome reads to the
reference genomes, most of the sequences of the SMTZ metagenome
were mapped to ANME-1 draft genomes, rather
than those of methanogens. Furthermore, the two copies of
the methyl-coenzyme M reductase gene (mcrA) segments
of the SMTZ metagenome were clustered with ANME-1b in
the phylogenetic cluster. These results indicate that ANME-
1b reads were miss-annotated to methanogens due to limitation
of database. Many of key genes necessary for reverse
methanogenesis were present in the SMTZ metagenome,
except for N5,N10-methenyl-H4MPT reductase (mer) and CoBCoM
heterodisulfide reductase subunits D and E (hdrDE). These data suggest that the ANME-1b represents the primary
player the anaerobic methane oxidation in the SMTZ,
of the methane hydrate-bearing sediment at the Ulleung
Basin, East Sea of Korea.