Neutrophilic Iron-Oxidizing “ Zetaproteobacteria ” and Mild Steel Corrosion in Nearshore Marine Environments

Abstract

Microbiologically influenced corrosion (MIC) of mild steel in seawater is an expensive and enduring problem. Little attention has been paid to the role of neutrophilic, lithotrophic, iron-oxidizing bacteria (FeOB) in MIC. The goal of this study was to determine if marine FeOB related to Mariprofundus are involved in this process. To examine this, field incubations and laboratory microcosm experiments were conducted. Mild steel samples incubated in nearshore environments were colonized by marine FeOB, as evidenced by the presence of helical iron-encrusted stalks diagnostic of the FeOB Mariprofundus ferrooxydans, a member of the candidate class "Zetaproteobacteria." Furthermore, Mariprofundus-like cells were enriched from MIC biofilms. The presence of Zetaproteobacteria was confirmed using a Zetaproteobacteria-specific small-subunit (SSU) rRNA gene primer set to amplify sequences related to M. ferrooxydans from both enrichments and in situ samples of MIC biofilms. Temporal in situ incubation studies showed a qualitative increase in stalk distribution on mild steel, suggesting progressive colonization by stalk-forming FeOB. We also isolated a novel FeOB, designated Mariprofundus sp. strain GSB2, from an iron oxide mat in a salt marsh. Strain GSB2 enhanced uniform corrosion from mild steel in laboratory microcosm experiments conducted over 4 days. Iron concentrations (including precipitates) in the medium were used as a measure of corrosion. The corrosion in biotic samples (7.4 ؎ 0.1 mM) was significantly higher than that in abiotic controls (5.0 ؎ 0.1 mM). These results have important implications for the role of FeOB in corrosion of steel in nearshore and estuarine environments. In addition, this work shows that the global distribution of Zetaproteobacteria is far greater than previously thought.

The iron-oxidizing proteobacteria

“…M. ferrooxydans is a marine, mesophilic, autotrophic iron oxidizer that has close morphological similarity (bean-shaped cells and stalk formation) to G. ferruginea, though phylogenetically it is very distant from the freshwater bacterium, and is affiliated with the Candidatus class 'Zetaproteobacteria' (Emerson et al, 2010). Another strain of M. ferrooxydans has recently been isolated from a near-shore marine environment (McBeth et al, 2011). In addition to M. ferrooxydans, other (as yet unclassified) marine strains of iron-oxidizing proteobacteria were described by Edwards et al (2003).…”

Genomic insights into the uncultivated marine Zetaproteobacteria at Loihi Seamount

“…To date, the Zetaproteobacteria have only been identified in habitats with high ferrous iron concentrations. Within this context, they have been detected in a wide range of environments from hydrothermal vent sites, such as Loihi Seamount, where they can dominate the microbial community (Rassa et al, 2009;Emerson and Moyer, 2010;McAllister et al, 2011;Fleming et al, 2013), to coastal environments, where they may be involved in biocorrosion of steel structures such as ships and pilings (Dang et al, 2011;McBeth et al, 2011).…”

Peeking under the Iron Curtain: Development of a Microcosm for Imaging the Colonization of Steel Surfaces by Mariprofundus sp. Strain DIS-1, an Oxygen-Tolerant Fe-Oxidizing Bacterium

“…The result of these processes is the need for more frequent maintenance of structures, such as piers, bridges, and pipelines, as well as an increased risk of catastrophic failure. The majority of the existing literature suggests that MIC is primarily a result of surface colonization by sulfate-reducing bacteria (SRB) (2-26), and while it is clear that the SRB play a major role in MIC, recent reports (2,3,15,17,27,28) have demonstrated the presence of lithotrophic Fe-oxidizing bacteria (FeOB) on steel surfaces impacted by MIC. FeOB utilize Fe(II) released from the steel surface as their primary energy source and are autotrophic, requiring only a few micronutrients in addition to Fe(II) to grow (29).…”

“…For example, a single, micrometer-sized cell of the marine FeOB Mariprofundus ferrooxydans can make at least 30 m of stalk per cell division (30); thus, there is the potential for these cells to produce a substantial amount of external structure as a result of their growth. It has been speculated that the mats created by the FeOB on steel surfaces serve as substrates for further colonization by diverse communities, including anaerobes such as sulfate-reducing bacteria, that result in accelerated MIC microbial communities (3,17,27).…”

“…Several studies have shown that during in situ incubations of mild steel, FeOB are capable of early colonization, and this pioneering colonization is followed by an increase in diversity of the surface community, including development of SRB populations (3,17,27). The FeOB that naturally colonize either mineral or steel surfaces are known to produce porous mats comprised of interwoven stalks of polysaccharides and poorly crystalline iron oxyhydroxides (17,23,28,30,31). For example, a single, micrometer-sized cell of the marine FeOB Mariprofundus ferrooxydans can make at least 30 m of stalk per cell division (30); thus, there is the potential for these cells to produce a substantial amount of external structure as a result of their growth.…”