Abstract
High iron and eutrophic conditions are reported as environmental factors leading to accelerated low-water corrosion, an enhanced form of near-shore microbial induced corrosion. To explore this hypothesis, we deployed flow-through colonization systems in laboratory-based aquarium tanks under a continuous flow of surface seawater from Santa Catalina Island, CA, USA, for periods of 2 and 6 months. Substrates consisted of mild steel – a major constituent of maritime infrastructure – and the naturally occurring iron sulfide mineral pyrite. Four conditions were tested: free-venting “high-flux” conditions; a “stagnant” condition; an “active” flow-through condition with seawater slowly pumped over the substrates; and an “enrichment” condition where the slow pumping of seawater was supplemented with nutrient rich medium. Electron microscopy analyses of the 2-month high flux incubations document coating of substrates with “twisted stalks,” resembling iron oxyhydroxide bioprecipitates made by marine neutrophilic Fe-oxidizing bacteria (FeOB). Six-month incubations exhibit increased biofilm and substrate corrosion in the active flow and nutrient enriched conditions relative to the stagnant condition. A scarcity of twisted stalks was observed for all 6 month slow-flow conditions compared to the high-flux condition, which may be attributable to oxygen concentrations in the slow-flux conditions being prohibitively low for sustained growth of stalk-producing bacteria. All substrates developed microbial communities reflective of the original seawater input, as based on 16S rRNA gene sequencing. Deltaproteobacteria sequences increased in relative abundance in the active flow and nutrient enrichment conditions, whereas Gammaproteobacteria sequences were relatively more abundant in the stagnant condition. These results indicate that (i) high-flux incubations with higher oxygen availability favor the development of biofilms with twisted stalks resembling those of marine neutrophilic FeOB and (ii) long-term nutrient stimulation results in substrate corrosion and biofilms with different bacterial community composition and structure relative to stagnant and non-nutritionally enhanced incubations. Similar microbial succession scenarios, involving increases in nutritional input leading to the proliferation of anaerobic iron and sulfur-cycling guilds, may occur at the nearby Port of Los Angeles and cause potential damage to maritime port infrastructure.
Highlights
Novel applications of microbial monitoring technologies are of particular importance near the port of Los Angeles (Figure 1A), the busiest port in the Western Hemisphere, where complex ecological responses to leaching iron and trophic variability can potentially negatively affect port infrastructure and associated local/global economies (Gubner and Beech, 1999; Beech and Sunner, 2004; Beech and Campbell, 2008)
We propose that H2S, the metabolic by-product of sulfate reducing bacteria (SRB), may lead to the recruitment of sulfide oxidizing bacteria (SOB) as the final step in a 3-tier (FeOB → SRB/FRB → SOB) ecological recruitment strategy for ferruginous substrate marine microbial colonization, a process likely accelerated under eutrophic conditions with potential ramifications for the enhanced microbial induced corrosion (MIC) state known as accelerated low-water corrosion (ALWC) near a globally important port
We conclude that surface pelagic microbial communities near the Port of Los Angeles exhibit a complex biologicalchemical-physical response to the combined effects of iron and nutritional enhancement simulating ALWC
Summary
Novel applications of microbial monitoring technologies are of particular importance near the port of Los Angeles (Figure 1A), the busiest port in the Western Hemisphere, where complex ecological responses to leaching iron and trophic variability can potentially negatively affect port infrastructure and associated local/global economies (Gubner and Beech, 1999; Beech and Sunner, 2004; Beech and Campbell, 2008). ALWC is a microbial induced corrosion (MIC) state presumably primed by eutrophic conditions conducive to the rapid recruitment and establishment of iron and sulfur cycling microbial cohorts capable of severe maritime infrastructure damage (Beech and Sunner, 2004; Little et al, 2007, 2013; Beech and Campbell, 2008; Dang et al, 2011). FeOOH bioprecipitates deposited under oxic, high Fe2+, and eutrophic conditions, may spur microbial corrosion of ferruginous maritime infrastructure (Blothe and Roden, 2009; Dang et al, 2011; McBeth et al, 2011; Marty et al, 2014)
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