Plastics select for distinct early colonizing microbial populations with reproducible traits across environmental gradients.

Little is known about early plastic biofilm assemblage dynamics and successional changes over time. By incubating virgin microplastics along oceanic transects and comparing adhered microbial communities with those of naturally occurring plastic litter at the same locations, we constructed gene catalogues to contrast the metabolic differences between early and mature biofilm communities. Early colonization incubations were reproducibly dominated by Alteromonadaceae and harboured significantly higher proportions of genes associated with adhesion, biofilm formation, chemotaxis, hydrocarbon degradation and motility. Comparative genomic analyses among the Alteromonadaceae metagenome assembled genomes (MAGs) highlighted the importance of the mannose-sensitive hemagglutinin (MSHA) operon, recognized as a key factor for intestinal colonization, for early colonization of hydrophobic plastic surfaces. Synteny alignments of MSHA also demonstrated positive selection for mshA alleles across all MAGs, suggesting that mshA provides a competitive advantage for surface colonization and nutrient acquisition. Large-scale genomic characteristics of early colonizers varied little, despite environmental variability. Mature plastic biofilms were composed of predominantly Rhodobacteraceae and displayed significantly higher proportions of carbohydrate hydrolysis enzymes and genes for photosynthesis and secondary metabolism. Our metagenomic analyses provide insight into early biofilm formation on plastics in the ocean and how early colonizers self-assemble, compared to mature, phylogenetically and metabolically diverse biofilms.

Sargasso Sea Vibrio bacteria: Underexplored potential pathovars in a perturbed habitat.

We fully sequenced the genomes of 16 Vibrio cultivars isolated from eel larvae, plastic marine debris (PMD), the pelagic brown macroalga Sargassum, and seawater samples collected from the Caribbean and Sargasso Seas of the North Atlantic Ocean. Annotation and mapping of these 16 bacterial genome sequences to a PMD-derived Vibrio metagenome-assembled genome created for this study showcased vertebrate pathogen genes closely-related to cholera and non-cholera pathovars. Phenotype testing of cultivars confirmed rapid biofilm formation, hemolytic, and lipophospholytic activities, consistent with pathogenic potential. Our study illustrates that open ocean vibrios represent a heretofore undescribed group of microbes, some representing potential new species, possessing an amalgam of pathogenic and low nutrient acquisition genes, reflecting their pelagic habitat and the substrates and hosts they colonize.

Large quantities of small microplastics permeate the surface ocean to abyssal depths in the South Atlantic Gyre.

Hundreds of studies have surveyed plastic debris in surface ocean gyre and convergence zones, however, comprehensive microplastics (MPs, ≤5 mm) assessments beneath these surface accumulation areas are lacking. Using in situ high-volume filtration, Manta net and MultiNet sampling, combined with micro-Fourier-transform-infrared imaging, we discovered a high abundance (up to 244.3 pieces per cubic meter [n m-3 ]) of small microplastics (SMPs, characteristically <100 µm) from the surface to near-sea floor waters of the remote South Atlantic Subtropical Gyre. Large horizontal and vertical variations in the abundances of SMP were observed, displaying inverse vertical trends in some cases. SMP abundances in pump samples were more than two orders of magnitude higher than large microplastics (LMPs, >300 µm) concurrently collected in MultiNet samples. Higher-density polymers (e.g., alkyd resins and polyamide) comprised >65% of the total pump sample count, highlighting a discrepancy between polymer compositions from previous ocean surface-based surveys, typically dominated by buoyant polymers such as polyethylene and polypropylene. Contrary to previous reports stating LMP preferentially accumulated at density gradients, SMP with presumably slower sinking rates are much less influenced by density gradients, thus resulting in a more even vertical distribution in the water column, and potentially longer residence times. Overall, our findings suggest that SMP is a critical and largely underexplored constituent of the oceanic plastic inventory. Additionally, our data support that weak current systems contribute to the formation of SMP hotspots at depth, implying a higher encounter rate for subsurface particle feeders. Our study unveils the prevalence of plastics in the entire water column, highlighting the urgency for more quantification of the deep-ocean MP, particularly the smaller size fraction, to better understand ecosystem exposure and to predict MP fate and impacts.