Novel Mode of Microbial Energy Metabolism: Organic Carbon Oxidation Coupled to Dissimilatory Reduction of Iron or Manganese

Abstract

A dissimilatory Fe(III)-and Mn(IV)-reducing microorganism was isolated from freshwater sediments of the Potomac River, Maryland. The isolate, designated GS-15, grew in defined anaerobic medium with acetate as the sole electron donor and Fe(III), Mn(IV), or nitrate as the sole electron acceptor. GS-15 oxidized acetate to carbon dioxide with the concomitant reduction of amorphic Fe(III) oxide to magnetite (Fe3O4). When Fe(III) citrate replaced amorphic Fe(III) oxide as the electron acceptor, GS-15 grew faster and reduced all of the added Fe(III) to Fe(II). GS-15 reduced a natural amorphic Fe(III) oxide but did not significantly reduce highly crystalline Fe(III) forms. Fe(III) was reduced optimally at pH 6.7 to 7 and at 30 to 35°C. Ethanol, butyrate, and propionate could also serve as electron donors for Fe(III) reduction. A variety of other organic compounds and hydrogen could not. MnO2 was completely reduced to Mn(II), which precipitated as rhodochrosite (MnCO3). Nitrate was reduced to ammonia. Oxygen could not serve as an electron acceptor, and it inhibited growth with the other electron acceptors. This is the first demonstration that microorganisms can completely oxidize organic compounds with Fe(III) or Mn(IV) as the sole electron acceptor and that oxidation of organic matter coupled to dissimilatory Fe(III) or Mn(IV) reduction can yield energy for microbial growth. GS-15 provides a model for how enzymatically catalyzed reactions can be quantitatively significant mechanisms for the reduction of iron and manganese in anaerobic environments.

High spatial resolution of distribution and interconnections between Fe‐ and N‐redox processes in profundal lake sediments

“…denitrification genes can only operate under anoxic conditions (Thamdrup, 2012) and Geobacter spp. are sensitive to oxygen (Lovley and Phillips, 1988). Therefore, microbial nitrate-reducing Fe(II) oxidation is physiologically restricted to anoxic conditions (Straub et al, 2004;Kappler et al, 2005a), which constrains nitrate-reducing Fe(II) oxidation to the zone of denitrification ( Fig.…”

Humics as an electron donor for anaerobic respiration

“…2H 2 O, 0.04; MgSO 4 . 7H 2 O, 0.1; NaHCO 3 1.8; Na 2 CO 3 , 0.5; along with vitamins and trace minerals as described previously (Lovley and Phillips, 1988). Fumarate (10 mM) was provided as an electron acceptor.…”

Bacteria batteries

“…Lovley and his team first discovered the mud-loving microbe on the banks of the Potomac River in 1987, and found that they were able to 'breathe' iron and other metals instead of air. 1 During this process, the researchers observed that an electrical charge was released, as electrons were transferred to the metals in the mud. In 2005, Lovley discovered the mechanism behind the charge: 2 the bacteria have thousands of tiny molecular wires called pili embedded in their surface that allow electrons to travel along them, much like a copper wire.…”