Microaerophilic Fe(II)-Oxidizing Zetaproteobacteria Isolated from Low-Fe Marine Coastal Sediments: Physiology and Composition of Their Twisted Stalks.
Microaerophilic Fe(II) oxidizers are commonly found in habitats containing elevated Fe(II) and low O2concentrations and often produce characteristic Fe mineral structures, so-called twisted stalks or tubular sheaths. Isolates originating from freshwater habitats are all members of theBetaproteobacteria, while isolates from marine habitats belong almost exclusively to theZetaproteobacteriaSo far, only a few isolates of marine microaerophilic Fe(II) oxidizers have been described, all of which are obligate microaerophilic Fe(II) oxidizers and have been thought to be restricted to Fe-rich systems. Here, we present two new isolates of marine microaerophilic Fe(II)-oxidizingZetaproteobacteriathat originate from typical coastal marine sediments containing only low Fe concentrations (2 to 11 mg of total Fe/g of sediment [dry weight]; 70 to 100 μM dissolved Fe2+in the porewater). The two novelZetaproteobacteriashare characteristic physiological properties of theZetaproteobacteriagroup, even though they come from low-Fe environments: the isolates are obligate microaerophilic Fe(II) oxidizers and, like most isolatedZetaproteobacteria, they produce twisted stalks. We found a low organic carbon content in the stalks (∼0.3 wt%), with mostly polysaccharides and saturated aliphatic chains (most likely lipids). The Fe minerals in the stalks were identified as lepidocrocite and possibly ferrihydrite. Immobilization experiments with Ni2+showed that the stalks can function as a sink for trace metals. Our findings show that obligate microaerophilic Fe(II) oxidizers belonging to theZetaproteobacteriagroup are not restricted to Fe-rich environments but can also be found in low-Fe marine environments, which increases their overall importance for the global biogeochemical Fe cycle.IMPORTANCESo far, only a few isolates of benthic marine microaerophilic Fe(II) oxidizers belonging to theZetaproteobacteriaexist, and most isolates were obtained from habitats containing elevated Fe concentrations. Consequently, it was thought that these microorganisms are important mainly in habitats with high Fe concentrations. The two novel isolates ofZetaproteobacteriathat are presented in the present study were isolated from typical coastal marine sediments that do not contain elevated Fe concentrations. This increases the knowledge about possible habitats in whichZetaproteobacteriacan exist. Furthermore, we show that the physiology and the typical organo-mineral structures (twisted stalks) that are produced by the isolates do not notably differ from the physiology and the cell-mineral structures of isolates from environments with high Fe concentrations. We also showed that the organo-mineral structures can function as a sink for trace metals.
Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
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Laufer
Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
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Nordhoff
Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
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Halama
Mineralogy-Petrology, Institute of Environmental Sciences, University of Freiburg, Freiburg im Breisgau, Germany.
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Martinez
Experimental Biogeochemistry, Bayreuth Center for Ecology and Environmental Research, University of Bayreuth, Bayreuth, Germany.
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Obst
Experimental Mineralogy, Mineralogy and Geodynamics, University of Tübingen, Tübingen, Germany.
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Nowak
ProVIS, Centre for Chemical Microscopy, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany.
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Stryhanyuk
ProVIS, Centre for Chemical Microscopy, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany.
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Richnow
Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany andreas.kappler@uni-tuebingen.de.|Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
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Kappler
D005296:Ferrous Compounds / Q000378:metabolism*; D019015:Geologic Sediments / Q000382:microbiology*; D007501:Iron; D010084:Oxidation-Reduction; D020560:Proteobacteria / Q000737:chemistry* / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D012623:Seawater / Q000382:microbiology*
D005296:Ferrous Compounds; D007501:Iron
geomicrobiology; iron oxidizers; marine microbiology; sediment