Marine biofilm bacterial community response and carbon steel loss following Deepwater Horizon spill contaminant exposure

Shipwreck ecology: Understanding the function and processes from microbes to megafauna

An estimated three million shipwrecks exist worldwide and are recognized as cultural resources and foci of archaeological investigations. Shipwrecks also support ecological resources by providing underwater habitats that can be colonized by diverse organisms ranging from microbes to megafauna. In the present article, we review the emerging ecological subdiscipline of shipwreck ecology, which aims to understand ecological functions and processes that occur on shipwrecks. We synthesize how shipwrecks create habitat for biota across multiple trophic levels and then describe how fundamental ecological functions and processes, including succession, zonation, connectivity, energy flow, disturbance, and habitat degradation, manifest on shipwrecks. We highlight future directions in shipwreck ecology that are ripe for exploration, placing a particular emphasis on how shipwrecks may serve as experimental networks to address long-standing ecological questions.

Microbially mediated metal corrosion

A wide diversity of microorganisms, typically growing as biofilms, has been implicated in corrosion, a multi-trillion dollar a year problem. Aerobic microorganisms establish conditions that promote metal corrosion, but most corrosion has been attributed to anaerobes. Microbially produced organic acids, sulfide and extracellular hydrogenases can accelerate metallic iron (Fe0) oxidation coupled to hydrogen (H2) production, as can respiratory anaerobes consuming H2 as an electron donor. Some bacteria and archaea directly accept electrons from Fe0 to support anaerobic respiration, often with c-type cytochromes as the apparent outer-surface electrical contact with the metal. Functional genetic studies are beginning to define corrosion mechanisms more rigorously. Omics studies are revealing which microorganisms are associated with corrosion, but new strategies for recovering corrosive microorganisms in culture are required to evaluate corrosive capabilities and mechanisms. Interdisciplinary studies of the interactions among microorganisms and between microorganisms and metals in corrosive biofilms show promise for developing new technologies to detect and prevent corrosion. In this Review, we explore the role of microorganisms in metal corrosion and discuss potential ways to mitigate it.

Substrate Specificity of Biofilms Proximate to Historic Shipwrecks

The number of built structures on the seabed, such as shipwrecks, energy platforms, and pipelines, is increasing in coastal and offshore regions. These structures, typically composed of steel or wood, are substrates for microbial attachment and biofilm formation. The success of biofilm growth depends on substrate characteristics and local environmental conditions, though it is unclear which feature is dominant in shaping biofilm microbiomes. The goal of this study was to understand the substrate- and site-specific impacts of built structures on short-term biofilm composition and functional potential. Seafloor experiments were conducted wherein steel and wood surfaces were deployed for four months at distances extending up to 115 m away from three historic (>50 years old) shipwrecks in the Gulf of Mexico. DNA from biofilms on the steel and wood was extracted, and metagenomes were sequenced on an Illumina NextSeq. A bioinformatics analysis revealed that the taxonomic composition was significantly different between substrates and sites, with substrate being the primary determining factor. Regardless of site, the steel biofilms had a higher abundance of genes related to biofilm formation, and sulfur, iron, and nitrogen cycling, while the wood biofilms showed a higher abundance of manganese cycling and methanol oxidation genes. This study demonstrates how substrate composition shapes biofilm microbiomes and suggests that marine biofilms may contribute to nutrient cycling at depth. Analyzing the marine biofilm microbiome provides insight into the ecological impact of anthropogenic structures on the seabed.

Proximity to built structures on the seabed promotes biofilm development and diversity

The rapidly expanding built environment in the northern Gulf of Mexico includes thousands of human built structures (e.g. platforms, shipwrecks) on the seabed. Primary-colonizing microbial biofilms transform structures into artificial reefs capable of supporting biodiversity, yet little is known about formation and recruitment of biofilms. Short-term seafloor experiments containing steel surfaces were placed near six structures, including historic shipwrecks and modern decommissioned energy platforms. Biofilms were analyzed for changes in phylogenetic composition, richness, and diversity relative to proximity to the structures. The biofilm core microbiome was primarily composed of iron-oxidizing Mariprofundus, sulfur-oxidizing Sulfurimonas, and biofilm-forming Rhodobacteraceae. Alpha diversity and richness significantly declined as a function of distance from structures. This study explores how built structures influence marine biofilms and contributes knowledge on how anthropogenic activity impacts microbiomes on the seabed.

Effect of Pseudomonas sp. on simulated tidal corrosion of X80 pipeline steel

Microbiologically influenced corrosion of pipeline steel in seawater has long been concerned by scholars all over the world, but there were few reports on the microorganism effect on marine tidal corrosion of steels. In this work, the effect of Pseudomonas sp. on static tidal corrosion of X80 pipeline steel were systematically studied using weight-loss, Fourier transform infrared spectroscopy (FTIR), electrochemical measurements, scanning electron microscopy (SEM) and ultra-deep field 3D microscope. The results manifested that after 720 h exposure to the marine tidal environment, the sessile Pseudomonas sp. counts multiplied with the elevation increase. The corrosion style of the steel in the inoculated environment was mainly localized corrosion. As a consequence of the higher bacteria number, the corrosion rate, pit depth and corrosion product thickness collectively enhanced. Pseudomonas sp. significantly accelerated uniform and localized corrosion of the steel in the marine tidal zone, and the acceleration role enhanced with the steel elevation in the tidal zones.

Introducing a "core steel microbiome" and community functional analysis associated with microbially influenced corrosion

Microorganisms attached to aquatic steel structures play key roles in nutrient cycling and structural degradation processes. Corrosion-causing microbes are often the focus of studies involving microbially influenced corrosion, yet the roles of remaining community members remain unclear. This study characterizes the composition and functional potential of a 'core steel microbiome' across stainless steel types (304 and 316) and historic shipwreck steel along salinity gradients in North Carolina estuaries. We found higher phylogenetic evenness and diversity on steel surfaces compared to sediment, and at lower salinities. The core steel microbiome was composed of heterotrophic generalist taxa, and community composition was most strongly influenced by salinity. Substrate type was a secondary factor becoming more influential at higher salinities. The core steel microbiome included members of Sphingobacteriia, Cytophagia, Anaerolineaceae, Verrucomicrobiaceae, Chitinophagaceae, and Rheinheimera. While salinity differences led to phylogenetic separations across microbial community assemblages, functional genes were conserved across salinity and steel type. Generalist taxa on steel surfaces likely provide functional stability and biofilm protection for the community with limited functional trade-offs compared to surrounding environments. Further, characterization of a core steel microbiome increases the understanding of these complex steel surface microbial communities and their similarities to core microbiomes in other environments.

Microbial Functional Responses in Marine Biofilms Exposed to Deepwater Horizon Spill Contaminants

Marine biofilms are essential biological components that transform built structures into artificial reefs. Anthropogenic contaminants released into the marine environment, such as crude oil and chemical dispersant from an oil spill, may disrupt the diversity and function of these foundational biofilms. To investigate the response of marine biofilm microbiomes from distinct environments to contaminants and to address microbial functional response, biofilm metagenomes were analyzed from two short-term microcosms, one using surface seawater (SSW) and the other using deep seawater (DSW). Following exposure to crude oil, chemical dispersant, and dispersed oil, taxonomically distinct communities were observed between microcosms from different source water challenged with the same contaminants and higher Shannon diversity was observed in SSW metagenomes. Marinobacter, Colwellia, Marinomonas, and Pseudoalteromonas phylotypes contributed to driving community differences between SSW and DSW. SSW metagenomes were dominated by Rhodobacteraceae, known biofilm-formers, and DSW metagenomes had the highest abundance of Marinobacter, associated with hydrocarbon degradation and biofilm formation. Association of source water metadata with treatment groups revealed that control biofilms (no contaminant) harbor the highest percentage of significant KEGG orthologs (KOs). While 70% functional similarity was observed among all metagenomes from both experiments, functional differences between SSW and DSW metagenomes were driven primarily by membrane transport KOs, while functional similarities were attributed to translation and signaling and cellular process KOs. Oil and dispersant metagenomes were 90% similar to each other in their respective experiments, which provides evidence of functional redundancy in these microbiomes. When interrogating microbial functional redundancy, it is crucial to consider how composition and function evolve in tandem when assessing functional responses to changing environmental conditions within marine biofilms. This study may have implications for future oil spill mitigation strategies at the surface and at depth and also provides information about the microbiome functional responses of biofilms on steel structures in the marine built environment.

Changes in microbial community in the presence of oil and chemical dispersant and their effects on the corrosion of API 5L steel coupons in a marine-simulated microcosm

The influence of crude oil and chemical dispersant was evaluated over planktonic bacteria and biofilms grown on API 5L steel surfaces in microcosm systems. Three conditions were simulated, an untreated marine environment and a marine environment with the presence of crude oil and a containing crude oil and chemical dispersant. The results of coupon corrosion rates indicated that in the oil microcosm, there was a high corrosion rate when compared with the other two systems. Analysis of bacterial communities by 16S rRNA gene sequencing described a clear difference between the different treatments. In plankton communities, the Bacilli and Gammaproteobacteria classes were the most present in numbers of operational taxonomic unit (OTUs). The Vibrionales, Oceanospirillales, and Alteromonadales orders were predominant in the treatment with crude oil, whereas in the microcosm containing oil and chemical dispersant, mainly members of Bacillales order were detected. In the communities analyzed from biofilms attached to the coupons, the most preponderant class was Alphaproteobacteria, followed by Gammaproteobacteria. In the control microcosm, there was a prevalence of the orders Rhodobacterales, Aeromonadales, and Alteromonadales, whereas in the dispersed oil and oil systems, the members of the order Rhodobacterales were present in a larger number of OTUs. These results demonstrate how the presence of a chemical dispersant and oil influence the corrosion rate and bacterial community structures present in the water column and biofilms grown on API 5L steel surfaces in a marine environment. KEY POINTS: • Evaluation of the effects of oil and chemical surfactants on the corrosion of API 5L. • Changes in microbial communities do not present corrosive biofilm on API 5L coupons.