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  Low-Light Anoxygenic Photosynthesis and Fe-S-Biogeochemistry in a Microbial Mat

Haas, S., de Beer, D., Klatt, J. M., Fink, A., Rench, R. M., Hamilton, T. L., et al. (2018). Low-Light Anoxygenic Photosynthesis and Fe-S-Biogeochemistry in a Microbial Mat. FRONTIERS IN MICROBIOLOGY, 9: 858. doi:10.3389/fmicb.2018.00858.

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 Creators:
Haas, Sebastian1, Author           
de Beer, Dirk2, Author           
Klatt, Judith Marlene2, Author           
Fink, Artur2, Author           
Rench, Rebecca McCauley, Author
Hamilton, Trinity L., Author
Meyer, Volker3, Author           
Kakuk, Brian, Author
Macalady, Jennifer L., Author
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1IMPRS MarMic, Max Planck Institute for Marine Microbiology, Max Planck Society, ou_2481704              
2Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society, ou_2481711              
3Max Planck Institute for Marine Microbiology, Max Planck Society, ou_2481692              

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 Abstract: We report extremely low-light-adapted anoxygenic photosynthesis in a thick microbial mat in Magical Blue Hole, Abaco Island, The Bahamas. Sulfur cycling was reduced by iron oxides and organic carbon limitation. The mat grows below the halocline/oxycline at 30 m depth on the walls of the flooded sinkhole. In situ irradiance at the mat surface on a sunny December day was between 0.021 and 0.084 mu mol photons m(-2) s(-1), and UV light (<400 nm) was the most abundant part of the spectrum followed by green wavelengths (475-530 nm). We measured a light-dependent carbon uptake rate of 14.5 nmol C cm(-2) d(-1). A 16S rRNA clone library of the green surface mat layer was dominated (74%) by a cluster (>97% sequence identity) of clones affiliated with Prosthecochloris, a genus within the green sulfur bacteria (GSB), which are obligate anoxygenic phototrophs. Typical photopigments of brown-colored GSB, bacteriochlorophyll e and (beta-)isorenieratene, were abundant in mat samples and their absorption properties are well-adapted to harvest light in the available green and possibly even UV-A spectra. Sulfide from the water column (3-6 mu mol L-1) was the main source of sulfide to the mat as sulfate reduction rates in the mats were very low (undetectable-99.2 nmol cm(-3) d(-1)). The anoxic water column was oligotrophic and low in dissolved organic carbon (175-228 mu mol L-1). High concentrations of pyrite (FeS2; 1-47 mu mol cm(-3)) together with low microbial process rates (sulfate reduction, CO2 fixation) indicate that the mats function as net sulfide sinks mainly by abiotic processes. We suggest that abundant Fe(III) (4.3-22.21 mu mol cm(-3)) is the major source of oxidizing power in the mat, and that abiotic Fe-S-reactions play the main role in pyrite formation. Limitation of sulfate reduction by low organic carbon availability along with the presence of abundant sulfide-scavenging iron oxides considerably slowed down sulfur cycling in these mats.

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 Dates: 2018
 Publication Status: Published online
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 Identifiers: ISI: 000431019300001
DOI: 10.3389/fmicb.2018.00858
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Title: FRONTIERS IN MICROBIOLOGY
Source Genre: Journal
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Pages: - Volume / Issue: 9 Sequence Number: 858 Start / End Page: - Identifier: ISSN: 1664-302X