Environmental predictors of electroactive bacterioplankton in small boreal lakes

Abstract

Extracellular electron transfer (EET) by electroactive bacteria in anoxic soils and sediments is an intensively researched subject, but EET's function in planktonic ecology has been less considered. Following the discovery of an unexpectedly high prevalence of EET genes in a bog lake's bacterioplankton, we hypothesized that the redox capacities of dissolved organic matter (DOM) enrich for electroactive bacteria by mediating redox chemistry. We developed the bioinformatics pipeline FEET (Find EET) to identify and summarize EET proteins from metagenomics data. We then applied FEET to several bog and thermokarst lakes and correlated EET protein occurrence values with environmental data to test our predictions. Our results provide evidence that DOM participates in EET by bacterioplankton. We found a similarly high prevalence of EET genes in most of these lakes, where oxidative EET strongly correlated with DOM. Numerous novel clusters of multiheme cytochromes that may enable EET were identified. Taxa previously not considered EET-capable were found to carry EET genes. We conclude that EET and DOM interactions are of major ecological importance to bacterioplankton in small boreal lakes, and that EET, particularly by methylotrophs and phototrophs, should be further studied and incorporated into both conceptual and quantitative methane emission models of melting permafrost.

Extracellular electron transfer genes expressed by candidate flocking bacteria in cable bacteria sediment

“…However, absence of observed transcripts is not equal to absence of the protein. Holophaga and Geothrix have been implicated in EET before and seen in bioanode communities (Olmsted et al, 2022; Arbour et al, 2020). The Holophaga and Geothrix may well perform EET as flockers.…”

Seasonal dynamics of the microbial methane filter in the water column of a eutrophic coastal basin

“…Although cryptic cycling could arguably obscure the supply of oxygen and alternative electron acceptors, nitrate is depleted in the suboxic zone (except for Aug/Sept), but iron oxides are potentially available (Żygadłowska, et al, 2023b). Furthermore, recent studies suggest that external electron transfer to or with dissolved organic matter (DOM) might increase the methane oxidation capacity in wetland and brackish sediments and even in the water column of humic bog lakes (Valenzuela et al, 2019;Olmsted et al, 2023;Pelsma et al, 2023). Considering the high sedimentation in the Scharendijke basin (Egger et al, 2016) and eutrophic state of the lake, external electron transfer linked to DOM and metal-oxides might be an additional mechanism supporting anaerobic methane oxidation especially in early summer (July).…”