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.

Deep-sea shipwrecks represent island-like ecosystems for marine microbiomes.

Biogeography of macro- and micro-organisms in the deep sea is, in part, shaped by naturally occurring heterogeneous habitat features of geological and biological origin such as seeps, vents, seamounts, whale and wood-falls. Artificial features including shipwrecks and energy infrastructure shape the biogeographic patterns of macro-organisms; how they influence microorganisms is unclear. Shipwrecks may function as islands of biodiversity for microbiomes, creating a patchwork of habitats with influence radiating out into the seabed. Here we show microbiome richness and diversity increase as a function of proximity to the historic deep-sea shipwreck Anona in the Gulf of Mexico. Diversity and richness extinction plots provide evidence of an island effect on microbiomes. A halo of core taxa on the seabed was observed up to 200 m away from the wreck indicative of the transition zone from shipwreck habitat to the surrounding environment. Transition zones around natural habitat features are often small in area compared to what was observed at Anona indicating shipwrecks may exert a large sphere of influence on seabed microbiomes. Historic shipwrecks are abundant, isolated habitats with global distribution, providing a means to explore contemporary processes shaping biogeography on the seafloor. This work is a case study for how built environments impact microbial biodiversity and provides new information on how arrival of material to the seafloor shapes benthic microbiomes.

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.

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

Steel marine structures provide foci of biodiversity when they develop into artificial reefs. Development begins with deposition of a biofilm. The effects of contaminants from oil spills on biofilm microbiomes, microbially-induced corrosion (MIC) and metal loss may impact preservation of marine metal structures. A microcosm experiment exposed biofilms on carbon steel disks (CSDs) to crude oil, dispersant, and dispersed oil to address their impacts on bacterial composition and metal loss and pitting. Biofilm diversity increased over time in all exposures. Community composition in dispersant and dispersed oil treatments deviated from the controls for the duration of a 12-week experiment. As biofilms matured, Pseudomonadaceae increased while Rhodobacteraceae decreased in abundance in dispersed oil treatments compared to the controls and dispersant treatments. Greatest mass loss and deepest pitting on CSDs were observed in dispersed oil treatments, suggesting impacts manifest as a consequence of increased MIC potential on carbon steel.