Genomic, physiologic, and kinetic investigations of marine iron-oxidizing bacteria
Date
2017
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Publisher
University of Delaware
Abstract
The Zetaproteobacteria are a widespread class of marine iron-oxidizing bacteria (FeOB). Although Zetaproteobacteria inhabit a wide range of environmental settings such as coastal sediment, deep-sea hydrothermal vents, and more recently, stratified water columns, little is known about the adaptations enabling Zetaproteobacteria to inhabit each of these niches. Additionally, the metabolic potential of Zetaproteobacteria has not been well quantified, making it difficult to assess their contributions to environmental Fe-cycling. Here we describe the isolation, characterization, and genomes of two new species from the Chesapeake Bay, Mariprofundus aestuarium CP-5 and Mariprofundus ferrinatatus CP-8, which are the first Zetaproteobacteria isolated from a pelagic environment. We looked for physiologic and genomic differences between the CP strains and benthic or subsurface Zetaproteobacteria to identify adaptations enabling strains CP-5 and CP-8 to overcome the challenges of living in a low Fe redoxcline with frequent O2 fluctuations due to tidal mixing. We found that the CP strains produce distinctive dreadlock-like Fe oxyhydroxide structures that are easily shed, which would help cells maintain suspension in the water column. The CP strains also have two gene clusters associated with biofilm formation (Wsp system and the Widespread Colonization Island) that are absent or rare in other Zetaproteobacteria. We propose that biofilm formation enables the CP strains to attach to FeS particles and form flocs, an advantageous strategy for scavenging Fe(II) and developing low [O2] microenvironments within more oxygenated waters. Besides identifying these adaptations, we measured strain CP-8 Fe(II) oxidation kinetics and show that strain CP-8 is capable of accelerating Fe(II) oxidation compared to abiotic processes alone at low (micromolar) [O2]. ☐ In addition to our work with Chesapeake Bay Zetaproteobacteria, we investigated FeOB at the East Pacific Rise (EPR). To identify Zetaproteobacteria at the EPR, we collected rust-colored Riftia tubes, rocks, and mats for FeOB enrichments and future metagenomic analyses. We also sought to examine the Fe(II) oxidation potential of EPR tubeworm endosymbionts that belong to the Gammaproteobacteria, but possess the putative Fe(II) oxidase, Cyc2. We purified Riftia endosymbionts to attempt FeOB enrichments and Fe(II) oxidation experiments, and our preliminary results suggest that these endosymbionts may be capable of oxidizing Fe(II). Together, our results provide insight on the Zetaproteobacteria living in different environmental settings, reveal niche-specific adaptations for Zetaproteobacteria to inhabit pelagic settings, and suggest other marine bacteria that may be capable of oxidizing Fe(II).
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Earth sciences