Fe(III) oxides protect fermenter-methanogen syntrophy against interruption by elemental sulfur via stiffening of Fe(II) sulfides produced by sulfur respiration.

Igarashi, Kensuke; Kuwabara, Tomohiko

Thermosipho globiformans (rod-shaped thermophilic fermenter) and Methanocaldococcus jannaschii (coccal hyperthermophilic hydrogenotrophic methanogen) established H-mediated syntrophy at 68 °C, forming exopolysaccharide-based aggregates. Electron microscopy showed that the syntrophic partners connected to each other directly or via intercellular bridges made from flagella, which facilitated transfer of H. Elemental sulfur (S) interrupted syntrophy; polysulfides abiotically formed from S intercepted electrons that were otherwise transferred to H to produce H, resulting in the generation of sulfide (sulfur respiration). However, Fe(III) oxides significantly reduced the interruption by S, accompanied by stiffening of Fe(II) sulfides produced by the reduction of Fe(III) oxides with the sulfur respiration-generated sulfide. Sea sand replacing Fe(III) oxides failed to generate stiffening or protect the syntrophy. Several experimental results indicated that the stiffening of Fe(II) sulfides shielded the liquid from S, resulting in methane production in the liquid. Field-emission scanning electron microscopy showed that the stiffened Fe(II) sulfides formed a network of spiny structures in which the microorganisms were buried. The individual fermenter rods likely produced Fe(II) sulfides on their surface and became local centers of a core of spiny structures, and the connection of these cores formed the network, which was macroscopically recognized as stiffening.

METHANOGENS; FERMENTATION; METHANOCALDOCOCCUS jannaschii; MICROBIAL exopolysaccharides; SYNTROPHISM; ELECTRON microscopy

Extremophiles, 2014, Vol 18, Issue 2, p351

1431-0651

Academic Journal

10.1007/s00792-013-0620-y