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 predicted EET protein‐encoding genes from metagenomics data. We then applied FEET to 36 bog and thermokarst lakes and correlated gene occurrence with environmental data to test our predictions. Our results provide indirect evidence that DOM may participate in bacterioplankton EET. We found a similarly high prevalence of genes encoding putative EET proteins 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 propose that EET and DOM interactions are of ecologically important to bacterioplankton in small boreal lakes, and that EET, particularly by methylotrophs and anoxygenic phototrophs, should be further studied and incorporated into methane emission models of melting permafrost.

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 August/September), 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 ).…”

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).…”

Metabolically diverse microorganisms mediate methylmercury formation under nitrate-reducing conditions in a dynamic hydroelectric reservoir

“…Under sulfidic conditions at the bottom of RM286 in 2017, the abundance of narG decreased again. The genes enabling Mn-reduction via external electron transfer (EET) are highly diverse and poorly constrained [ 54 , 76 ], making it difficult to use metagenomics to identify potential Mn reduction hotspots. However, homologs of extE , which is involved in Mn-reduction [ 77 ], were most abundant at 50 m at RM300 in 2019, coincident with a peak in filter-passing Mn (Table S4 ).…”

“…Metabolic genes were identified using Hidden Markov Models (HMMs) and confirmed phylogenetically (Table S4 ). Metabolic annotations of mOTUs were done using kofamscan [ 51 ], a custom HMM set with hmmer [ 52 ], METABOLIC [ 53 ], and FEET [ 54 ]. Major terminal electron-accepting process (TEAP) gene annotations were confirmed phylogenetically.…”