Methanogens are an important biogenic source of methane,
especially in estuarine waters across a river-to-sea gradient.
However, the diversity and trophic strategy of methanogens
in this gradient are not clear. In this study, the diversity and
trophic strategy of methanogens in sediments across the
Yellow River (YR) to the Bohai Sea (BS) gradient were investigated
by high-throughput sequencing based on the 16S
rRNA gene. The results showed that the diversity of methanogens
in sediments varied from multitrophic communities
in YR samples to specific methylotrophic communities in BS
samples. The methanogenic community in YR samples was
dominated by Methanosarcina, while that of BS samples was
dominated by methylotrophic Methanococcoides. The distinct
methanogens suggested that the methanogenic community
of BS sediments did not originate from YR sediment
input. High-throughput sequencing of the mcrA gene revealed
that active Methanococcoides dominated in the BS enrichment
cultures with trimethylamine as the substrate, and methylotrophic
Methanolobus dominated in the YR enrichment
cultures, as detected to a limited amount in in situ sediment
samples. Methanosarcina were also detected in this gradient
sample. Furthermore, the same species of Methanosarcina
mazei, which was widely distributed, was isolated from the
area across a river-to-sea gradient by the culture-dependent method . In summary, our results showed that a distribution
of diverse methanogens across a river-to-sea gradient may
shed light on adaption strategies and survival mechanisms
in methanogens.