Lanthanide Distribution is an Important Driver on Aerobic Methylotroph Community Composition and Distribution in the Sargasso Sea

The Sargasso Sea is an extremely oligotrophic region of the subtropical North Atlantic. It is the subject of a monthly time-series at the Bermuda Atlantic Time Series Station (31°40′ N, 64°10′ W). Consistent phosphate limitation in the euphotic zone of this region, influenced by the seasonal stratification and mixed layer interaction with the 18˚C Mode Water, causes generally low primary productivity, with a large portion of the water column biomass being attributable to prokaryotes and pico-eukaryotes. Prokaryotic methylotrophs are an understudied part of the Sargasso Sea microbial community. Methane and methanol oxidizing bacteria have an important role in regulation and cycling of methane and maintaining the nanomolar level concentrations of this potent greenhouse gas.

In addition to their widespread role in regulation of methane levels, aerobic bacterial methanotrophs and methylotrophs have recently garnered attention due to their usage of low-atomic-weight lanthanides as the catalytic centre of the xoxF family of methanol dehydrogenase isoforms (xoxF-meDH). The only previously known methanol dehydrogenase, mxa-MeDH, uses a PQQ cofactor like its xoxF homolog, but has Ca²⁺ as a cofactor. xoxF expression has been observed in a variety of environments (e.g. marine coastal areas, geothermal mudpots, open ocean) but its presence and expression has yet to be definitely tied to biogeochemical factors.

In this study, we report the rare earth element distribution at BATS at the highest vertical resolution to date. This high vertical and temporal resolution, in conjunction with our corresponding CH₄ and N₂O profiles, allows us to investigate the control of REEs on methanotrophic activity within the water column at BATS. Understanding how these environmental parameters correspond with each other provides an important look at the contribution of REEs to methane cycling in the marine environment. These profiles will also be correlated to V3 and V4 16s analysis of community composition through the entire water column. Furthermore, the modern water column conditions provide us with a platform to investigate the utility of REE series fractionation as a metabolic signature that may persist through geologic time.