Sulfate-dependant microbially induced corrosion of mild steel in the deep sea: a 10-year microbiome study

Background Metal corrosion in seawater has been extensively studied in surface and shallow waters. However, infrastructure is increasingly being installed in deep-sea environments, where extremes of temperature, salinity, and high hydrostatic pressure increase the costs and logistical challenges associated with monitoring corrosion. Moreover, there is currently only a rudimentary understanding of the role of microbially induced corrosion, which has rarely been studied in the deep-sea. We report here an integrative study of the biofilms growing on the surface of corroding mooring chain links that had been deployed for 10 years at ~2 km depth and developed a model of microbially induced corrosion based on flux-balance analysis. Methods We used optical emission spectrometry to analyze the chemical composition of the mooring chain and energy-dispersive X-ray spectrometry coupled with scanning electron microscopy to identify corrosion products and ultrastructural features. The taxonomic structure of the microbiome was determined using shotgun metagenomics and was confirmed by 16S amplicon analysis and quantitative PCR of the dsrB gene. The functional capacity was further analyzed by generating binned, genomic assemblies and performing flux-balance analysis on the metabolism of the dominant taxa. Results The surface of the chain links showed intensive and localized corrosion with structural features typical of microbially induced corrosion. The microbiome on the links differed considerably from that of the surrounding sediment, suggesting selection for specific metal-corroding biofilms dominated by sulfur-cycling bacteria. The core metabolism of the microbiome was reconstructed to generate a mechanistic model that combines biotic and abiotic corrosion. Based on this metabolic model, we propose that sulfate reduction and sulfur disproportionation might play key roles in deep-sea corrosion. Conclusions The corrosion rate observed was higher than what could be expected from abiotic corrosion mechanisms under these environmental conditions. High corrosion rate and the form of corrosion (deep pitting) suggest that the corrosion of the chain links was driven by both abiotic and biotic processes. We posit that the corrosion is driven by deep-sea sulfur-cycling microorganisms which may gain energy by accelerating the reaction between metallic iron and elemental sulfur. The results of this field study provide important new insights on the ecophysiology of the corrosion process in the deep sea.

Metagenomic Analysis of The Effects of Salinity On Microbial Diversity and Functional Gene Diversity in Kongsfjorden Estuary

Due to the inflow of meltwater from the Midre Lovénbreen glacier upstream of Kongsfjorden, the salinity of Kongsfjorden increases from the estuary to the interior of the fjord. Our goal was to determine which bacterial taxa and metabolism-related gene abundance were affected by changes in salinity, and whether salinity is correlated with genes related to nitrogen and sulfur cycling in fjord ecosystem using metagenomic analysis. Our data indicate that changes in salinity may affect some bacterial taxa, such as the relative abundance of Alphaproteobacteria and Deltaproteobacteria is higher at high salinity sites, while the relative abundance of Gammaproteobacteria and Betaproteobacteria is more dominant at low salinity sites. In addition, the relative abundance of some bacteria at the high and low salinity sites was different at the family level. For example, Rhodobacteraceae, Pseudoalteromonadaceae, Flavobacteriaceae, Vibrionaceae at the high salinity site Colwelliaceae, Chromatiaceae and Alteromonadaceae at the low salinity site are affected by salinity. In terms of functional gene diversity, our study proved that salinity could affect the relative abundance of related genes by affecting the metabolic mechanism of microorganisms. In addition to salinity, functional attributes of microorganisms themselves were also important factors affecting the relative abundance of metabolism-related genes. In addition, salinity has a certain effect on the relative abundance of genes related to nitrogen and sulfur cycling.

Aqueous system-level processes and prokaryote assemblages in the ferruginous and sulfate-rich bottom waters of a post-mining lake

In the aqueous oligotrophic ecosystem of a post-mining lake (Lake Medard, Czechia), reductive Fe(II) dissolution outpaces sulfide generation from microbial sulfate reduction (MSR), and ferruginous conditions occur without quantitative sulfate depletion. An isotopically constrained estimate of the rates of sulfate reduction (SRR) suggests that despite a high genetic potential, this respiration pathway is limited by the rather low amounts of metabolizable organic carbon. This points to substrate competition exerted by iron and nitrogen respiring prokaryotes. Yet, the microbial succession across the nitrogenous and ferruginous zones of the bottom water column also indicates sustained genetic potential for chemolithotrophic sulfur oxidation. Therefore, our isotopic SRR estimates could be rather portraying high rates of anoxic sulfide oxidation to sulfate, probably accompanied by microbially induced disproportionation of S intermediates. Near and at the anoxic sediment-water interface, vigorous sulfur cycling can be fuelled by ferric and manganic particulate matter and redeposited siderite stocks. Sulfur oxidation and disproportionation then appear to prevent substantial stabilization of iron monosulfides as pyrite but can enable the interstitial precipitation of small proportions of equant microcrystalline gypsum. This latter mineral isotopically fingerprints sulfur oxidation proceeding at near equilibrium with the ambient anoxic waters, whilst authigenic pyrite-sulfur displays a 38 to 27 ‰ isotopic offset from ambient sulfate, suggestive of incomplete MSR and likely reflective also of an open sulfur cycling system. Pyrite-sulfur fractionation decreases with increased reducible reactive iron in the sediment. In the absence of ferruginous coastal zones today, the current water column redox stratification in the post-mining Lake Medard has scientific value for (i) testing emerging hypotheses on how a few interlinked biogeochemical cycles operated in nearshore paleoenvironments during redox transitional states; and (ii) to acquire insight on how similar early diagenetic redox proxy signals developed in sediments affected by analogue transitional states in ancient water columns.

Sulfate-dependant microbially induced corrosion of mild steel in the deep-sea: a 10-year microbiome study

Background Metal corrosion in seawater has been extensively studied in surface and shallow waters. However, infrastructure is increasingly being installed in deep-sea environments, where extremes of temperature, salinity and high hydrostatic pressure increase the costs and logistical challenges associated with monitoring corrosion. Moreover, there is currently only a rudimentary understanding of the role of microbially induced corrosion, which has rarely been studied in the deep-sea. We report here an integrative study of the biofilms growing on the surface of corroding mooring chain links that had been deployed for 10 years at ~2 km depth and developed a model of microbially induced corrosion based on flux-balance analysis. Methods We used optical emission spectrometry to analyse the chemical composition of the mooring chain and energy-dispersive X-ray spectrometry coupled with scanning electron microscopy to identify corrosion products and ultrastructural features. The taxonomic structure of the microbiome was determined using shotgun metagenomics and was confirmed by 16S amplicon analysis and quantitative PCR of the dsrB gene. The functional capacity was further analysed by generating binned, genomic assemblies and performing flux-balance analysis on the metabolism of the dominant taxa. Results The surface of the chain links showed intensive and localised corrosion with structural features typical of microbially induced corrosion. The microbiome on the links differed considerably from that of the surrounding sediment, suggesting selection for specific metal-corroding biofilms dominated by sulfur-cycling bacteria. The core metabolism of the microbiome was reconstructed to generate a mechanistic model that combines biotic and abiotic corrosion. Based on this metabolic model, we propose that sulfate reduction and sulfur disproportionation might play key roles in deep-sea corrosion. Conclusions The corrosion rate observed was higher than what could be expected from abiotic corrosion mechanisms under these environmental conditions. High corrosion rate and the form of corrosion (deep pitting) suggest that the corrosion of the chain links was driven by both abiotic and biotic processes. We posit that the corrosion is driven by deep-sea sulfur-cycling microorganisms which may gain energy by accelerating the reaction between metallic iron and elemental sulfur. The results of this field study provide important new insights on the ecophysiology of the corrosion process in the deep sea.