Abstract
Cable bacteria (Deltaproteobacteria, Desulfobulbaceae) are long filamentous sulfur-oxidizing bacteria that generate long-distance electric currents running through the bacterial filaments. This way, they couple the oxidation of sulfide in deeper sediment layers to the reduction of oxygen or nitrate near the sediment-water interface. Cable bacteria are found in a wide range of aquatic sediments, but an accurate procedure to assess their abundance is lacking. We developed a qPCR approach that quantifies cable bacteria in relation to other bacteria within the family Desulfobulbaceae. Primer sets targeting cable bacteria, Desulfobulbaceae and the total bacterial community were applied in qPCR with DNA extracted from marine sediment incubations. Amplicon sequencing of the 16S rRNA gene V4 region confirmed that cable bacteria were accurately enumerated by qPCR, and suggested novel diversity of cable bacteria. The conjoint quantification of current densities and cell densities revealed that individual filaments carry a mean current of ∼110 pA and have a cell specific oxygen consumption rate of 69 fmol O2 cell–1 day–1. Overall, the qPCR method enables a better quantitative assessment of cable bacteria abundance, providing new metabolic insights at filament and cell level, and improving our understanding of the microbial ecology of electrogenic sediments.
Highlights
Cable bacteria are long, multicellular, filamentous bacteria that transport electrons from cell-tocell along the filament over distances of up to several centimeters (Pfeffer et al, 2012; Bjerg et al, 2018; Meysman, 2018; Meysman et al, 2019)
We explore the use of qPCR as a method to quantify the abundance of cable bacteria in marine and salt marsh sediments
The ELF645wF primer is an extension of primer ELF645F targeting cable bacteria (Pfeffer et al, 2012; Marzocchi et al, 2014) to accommodate C instead of T at position 2 as present in the 16S rRNA gene sequence of Ca
Summary
Multicellular, filamentous bacteria that transport electrons from cell-tocell along the filament over distances of up to several centimeters (Pfeffer et al, 2012; Bjerg et al, 2018; Meysman, 2018; Meysman et al, 2019). QPCR Quantification of Cable Bacteria in the pore water Part of this aqueous Fe2+ will diffuse to the oxic sediment surface, where it will reoxidize and reprecipitate as iron(III) (hydr)oxides (Seitaj et al, 2015; Rao et al, 2016). This precipitated iron(III) (hydr)oxide plays a critical role in coastal ecosystems experiencing seasonal hypoxia, because it intercepts sulfide that is released from the sediment to the bottom water, and reduces the risk of sulfide toxicity to fauna in seasonally stratified coastal systems (Seitaj et al, 2015) Given this strong environmental impact of cable bacteria, it is adamant to accurately quantify both their abundance and activity in aquatic sediments. This allows to estimate the electron flow and metabolic activity at the single filament and single cell level
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