Light rare earth element depletion during Deepwater Horizon blowout methanotrophy

Abstract

Rare earth elements have generally not been thought to have a biological role. However, recent work has demonstrated that the light REEs (LREEs: La, Ce, Pr, and Nd) are essential for at least some methanotrophs, being co-factors in the XoxF type of methanol dehydrogenase (MDH). We show here that dissolved LREEs were significantly removed in a submerged plume of methane-rich water during the Deepwater Horizon (DWH) well blowout. Furthermore, incubation experiments conducted with naturally methane-enriched waters from hydrocarbon seeps in the vicinity of the DWH wellhead also showed LREE removal concurrent with methane consumption. Metagenomic sequencing of incubation samples revealed that LREE-containing MDHs were present. Our field and laboratory observations provide further insight into the biochemical pathways of methanotrophy during the DWH blowout. Additionally, our results are the first observations of direct biological alteration of REE distributions in oceanic systems. In view of the ubiquity of LREE-containing MDHs in oceanic systems, our results suggest that biological uptake of LREEs is an overlooked aspect of the oceanic geochemistry of this group of elements previously thought to be biologically inactive and an unresolved factor in the flux of methane, a potent greenhouse gas, from the ocean.

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

“…These observations support the assumption that ε Nd is conservative or "quasi-conservative" in the oceans and will trace water masses in a manner similar to temperature and salinity (Frank, 2002;Goldstein and Hemming, 2003). Furthermore, elemental Nd is assumed to have negligible bioactivity, although recent work suggests that there are important caveats to this assumption (Shiller et al, 2017). However, because of the concerted efforts invested into measuring neodymium in the oceans as well as within sedimentary archives, inconsistencies between the observed distributions and the assumptions inherent in the use of the Nd as a tracer are becoming increasingly apparent.…”

Oil seepage and carbonate formation: A case study from the southern Gulf of Mexico

“…Moreover, Shiller et al . () observed preferred and active uptake of the LREEs by aerobic methanotrophs from the water column in response to the Deepwater Horizon oil spill (Gulf of Mexico), further suggesting that LREE enrichment may be related to the metabolism of oil‐consuming microbial communities or be related to the oil itself.…”

“…Finely crystalline grey aragonite in the present study represents a modern equivalent of yellow aragonite and calcite, which have been identified in numerous Phanerozoic methaneseep deposits (Zwicker et al, 2018, and references therein). Moreover, Shiller et al (2017) observed preferred and active uptake of the LREEs by aerobic methanotrophs from the water column in response to the Deepwater Horizon oil spill (Gulf of Mexico), further suggesting that LREE enrichment may be related to the metabolism of oil-consuming microbial communities or be related to the oil itself.…”

Similar but Not the Same: First Kinetic and Structural Analyses of a Methanol Dehydrogenase Containing a Europium Ion in the Active Site

“…The plumes in the ocean led to a bloom of methanotrophic bacteria, and a recent study showed that, concurrently with methane consumption, a depletion of light rare earth elements (REEs: La, Ce, Pr, and Nd) from the surrounding seawater was observed . This phenomenon can be explained in terms of the biological role of REEs for methanotrophic and methylotrophic bacteria . These bacteria utilize C1 compounds, such as methane and methanol, as an energy source.…”