A Novel Shewanella Isolate Enhances Corrosion by Using Metallic Iron as the Electron Donor with Fumarate as the Electron Acceptor

Abstract

The involvement of spp. in biocorrosion is often attributed to their Fe(III)-reducing properties, but they could also affect corrosion by using metallic iron as an electron donor. Previously, we isolated strain 4t3-1-2LB from an acetogenic community enriched with Fe(0) as the sole electron donor. Here, we investigated its use of Fe(0) as an electron donor with fumarate as an electron acceptor and explored its corrosion-enhancing mechanism. Without Fe(0), strain 4t3-1-2LB fermented fumarate to succinate and CO, as was shown by the reaction stoichiometry and pH. With Fe(0), strain 4t3-1-2LB completely reduced fumarate to succinate and increased the Fe(0) corrosion rate (7.0 ± 0.6)-fold in comparison to that of abiotic controls (based on the succinate-versus-abiotic hydrogen formation rate). Fumarate reduction by strain 4t3-1-2LB was, at least in part, supported by chemical hydrogen formation on Fe(0). Filter-sterilized spent medium increased the hydrogen generation rate only 1.5-fold, and thus extracellular hydrogenase enzymes appear to be insufficient to explain the enhanced corrosion rate. Electrochemical measurements suggested that strain 4t3-1-2LB did not excrete dissolved redox mediators. Exchanging the medium and scanning electron microscopy (SEM) imaging indicated that cells were attached to Fe(0). It is possible that strain 4t3-1-2LB used a direct mechanism to withdraw electrons from Fe(0) or favored chemical hydrogen formation on Fe(0) through maintaining low hydrogen concentrations. In coculture with an strain, strain 4t3-1-2LB did not enhance acetogenesis from Fe(0). This work describes a strong corrosion enhancement by a strain through its use of Fe(0) as an electron donor and provides insights into its corrosion-enhancing mechanism. spp. are frequently found on corroded metal structures. Their role in microbial influenced corrosion has been attributed mainly to their Fe(III)-reducing properties and, therefore, has been studied with the addition of an electron donor (lactate). spp., however, can also use solid electron donors, such as cathodes and potentially Fe(0). In this work, we show that the electron acceptor fumarate supported the use of Fe(0) as the electron donor by strain 4t3-1-2LB, which caused a (7.0 ± 0.6)-fold increase of the corrosion rate. The corrosion-enhancing mechanism likely involved cell surface-associated components in direct contact with the Fe(0) surface or maintenance of low hydrogen levels by attached cells, thereby favoring chemical hydrogen formation by Fe(0). This work sheds new light on the role of spp. in biocorrosion, while the insights into the corrosion-enhancing mechanism contribute to the understanding of extracellular electron uptake processes.

Iron Corrosion via Direct Metal-Microbe Electron Transfer

“…However, the enrichment of the microbes proposed to be capable of direct electron transfer on Fe(0) may have selected for other characteristics that promote Fe(0) oxidation with the production of H 2 (10). For example, many of the microbes proposed to be capable of direct electron transfer from Fe(0) appear to be more effective in colonizing surfaces, which may result in more effective H 2 removal at the point of production.…”

Role of aspartate ammonia-lyase in Pasteurella multocida

“…Amino acid homology analysis suggested that the structural and evolutionary relationships of aspA were closely related to fumarase (fumC) [24], which is known to be related to iron acquisition in many bacteria [25][26][27][28]. As their common product, fumarate could act as an electron acceptor during iron-uptake [29]. These results suggested that aspA might also play a role in iron acquisition in P. multocida.…”

Carbon steel corrosion by bacteria from failed seal rings at an offshore facility

“…Shewanella species are well known for their metabolic versatility to utilise a variety of electron acceptors, which include nitrate, nitrite, thiosulphate, elemental sulphur, iron (III), Manganese (III), fumarate, among others 58 , 63 – 65 . Additionally, Shewanella can use the metal as electron donor by secreting electron shuttles such as riboflavins, or by producing conductive filaments (nanowires) 66 .…”