Methylotrophic Methanogens in the Water Column of an Upwelling Zone with a Strong Oxygen Gradient Off Central Chile

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The growing biogeochemical and economic importance of biogenic methane contained in gas hydrates necessitates a better understanding of the microorganisms involved in the last phase of organic matter degradation. Here, the distribution and relative abundance of methylotrophic methane-producing Archaea (mMPA) were studied in an upwelling area off central Chile by rRNA dot blot hybridization. The mMPA were detected mostly during active upwelling periods, and were more abundant in the deeper layer of the water column (>50 m), where they represented 〜10% of the prokaryote rRNA extractable from seawater samples in the oxygen minimum zone (OMZ). Significant correlations were found between the concentration of rRNA from mMPA and (i) nitrate concentration (r=-0.54, p=0.0392) and (ii) temperature (r=-0.51, p=0.0267). Enrichment experiments with water samples from the OMZ were carried out to evaluate the cellular viability of mMPA. These experiments showed that some of these Archaea remain viable in the planktonic environment although not essentially associated with fecal pellets or any type of compact macroaggregate. The results suggest that mMPA in the water column come mostly from sediment and that a fraction correspond to psychrophilic varieties of facultative methylotrophs.
日本微生物生態学会の論文