Biogeochemical impact of cable bacteria on coastal Black Sea sediment

Abstract

Abstract. Cable bacteria can strongly alter sediment biogeochemistry. Here, we used laboratory incubations to determine the potential impact of their activity on the cycling of iron (Fe), phosphorus (P) and sulfur (S). Microsensor depth profiles of oxygen, sulfide and pH in combination with electric potential profiling and fluorescence in situ hybridisation (FISH) analyses showed a rapid development (<5 d) of cable bacteria, followed by a long period of activity (>200 d). During most of the experiment, the current density correlated linearly with the oxygen demand. Sediment oxygen uptake was attributed to the activity of cable bacteria and the oxidation of reduced products from the anaerobic degradation of organic matter, such as ammonium. Pore water sulfide was low (< 5 µM) throughout the experiment. Sulfate reduction acted as the main source of sulfide for cable bacteria. Pore water Fe2+ reached levels of up to 1.7 mM during the incubations, due to the dissolution of FeS (30 %) and siderite, an Fe carbonate mineral (70 %). Following the upward diffusion of Fe2+, a surface enrichment of Fe oxides formed. Hence, besides FeS, siderite may act as a major source of Fe for Fe oxides in coastal surface sediments where cable bacteria are active. Using µXRF, we show that the enrichments in Fe oxides induced by cable bacteria are located in a thin subsurface layer of 0.3 mm. We show that similar subsurface layers enriched in Fe and P are also observed at field sites where cable bacteria were recently active and little bioturbation occurs. This suggests that such subsurface Fe oxide layers, which are not always visible to the naked eye, could potentially be a marker for recent activity of cable bacteria.

Microbial succession in a marine sediment: Inferring interspecific microbial interactions with marine cable bacteria

“…Cable bacteria grow as long multicellular filaments and act as centimetre‐scale electrical conductors in aquatic sediments, providing a conduit for rapid electron transport from deeper sulfidogenic horizons up to an oxic sediment surface (Nielsen et al, 2010 ). Since their discovery about a decade ago (Pfeffer et al, 2012 ), cable bacteria have been observed in a wide range of depositional sedimentary environments (Aller et al, 2019 ; Burdorf et al, 2016 ; Hermans et al, 2020 ; Scholz et al, 2021 ), and frequently at high cell densities (Malkin et al, 2017 ). Especially where these bacteria achieve high biomass, their metabolic activity can drive intense localized changes in pH and strongly influence the cycling of oxygen, sulfur, iron, manganese, phosphorus, carbonate, organic carbon, and trace metals (Huo et al, 2022 ; Rao et al, 2016 ; Risgaard‐Petersen et al, 2012 ; Sulu‐Gambari et al, 2016a , 2016b ; van de Velde et al, 2016 ), with impacts on the ecosystem level (Seitaj et al, 2015 ).…”

Sediment Nutrient Flux Rates in a Shallow, Turbid Lake Are More Dependent on Water Quality Than Lake Depth

“…Additionally, the strong redox gradients at the water-sediment interface and potentially high iron and sulfate found in Delta soils [68] suggests that other microbial-mediated P release pathways may be occurring. For example, cable bacteria and Beggiatoacaea bacteria are known mediators of P release from sediments through the enhanced formation of iron and sulfur oxides [69].…”

Biogeochemical impacts of fish farming on coastal sediments: Insights into the functional role of cable bacteria

“…When the bottom water turns anoxic, this iron firewall captures the sulfide diffusing upward and this can prevent/delay the escape of sulfide from the sediment over a period of weeks ( Seitaj et al, 2015 ). In doing so, the detrimental effects of hypoxia and euxinia, both in the benthic and pelagic environments, are alleviated naturally ( Marzocchi et al, 2018 ; Hermans et al, 2020 ). The reduction of sulfide levels in sediments by e-SOx likely favors the growth of seagrass and mussel beds, and the re-colonization of benthic macro- and meiofauna ( Seitaj et al, 2015 ; Malkin et al, 2017 ; Martin et al, 2018 ; Bonaglia et al, 2020 ).…”