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Applied and Environmental Microbiology, June 2002, p. 2972-2981, Vol. 68, No. 6
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.6.2972-2981.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Experimental Study of Interactions between Purple and Green Sulfur Bacteria in Sandy Sediments Exposed to Illumination Deprived of Near-Infrared Wavelengths

Astrid Massé,1 Olivier Pringault,1,2,{dagger} and Rutger de Wit1*

Laboratoire d'Océanographie Biologique, CNRS-UMR 5805 Université Bordeaux 1, F-33120 Arcachon, France,1 Microsensor Group, Max-Planck-Institut für Marine Mikrobiologie, D-28359 Bremen, Germany2

Received 1 November 2001/ Accepted 2 April 2002

Sedimentary biofilms of the green sulfur bacterium Prosthecochloris aestuarii strain CE 2404, the purple sulfur bacterium Thiocapsa roseopersicina strain 5811, and a mixed culture of both were cultured in fine sand (100- to 300-µm grain size) within counter gradients of oxygen and sulfide. The artificial sediments were exposed to illumination deprived of near-infrared light (NIR) by filtering out the wavelengths longer than 700 nm to simulate the critical light conditions in submerged aquatic sediments. A 16 h of visible light-8 h of dark regimen was used. We studied the effects of these light conditions on the metabolisms of and interactions between both species by comparing the single species biofilms with the mixed biofilm. The photosynthesis rates of P. aestuarii were shown to be highly limited by the imposed light conditions, because the sulfide photooxidation rates were strongly stimulated when NIR was added. T. roseopersicina performed both aerobic chemosynthesis and photosynthesis, but the photosynthesis rates were low and poorly stimulated by the addition of NIR. This species decreased the penetration depth of oxygen in the sediment by about 1 mm by actively respiring oxygen. This way, the strict anaerobe P. aestuarii was able to grow closer to the surface in the mixed culture. As a result, P. aestuarii benefited from the presence of T. roseopersicina in the mixed culture, which was reflected by an increase in the biomass. In contrast, the density of the latter species was almost completely unaffected by the interaction. Both species coexisted in a layer of the same depth in the mixed culture, and the ecological and evolutionary implications of coexistence are discussed.

* Corresponding author. Mailing address: Laboratoire d'Océanographie Biologique, CNRS-UMR 5805 Université Bordeaux 1, 2 rue du Professeur Jolyet, F-33120 Arcachon, France. Phone: 33 5 56 22 39 09. Fax: 33 5 56 83 51 04. E-mail: r.de-wit{at}epoc.u-bordeaux.fr.

{dagger} Present address: Centre IRD de Nouméa, BP A5, 98848 Nouméa Cedex, New Caledonia.

Applied and Environmental Microbiology, June 2002, p. 2972-2981, Vol. 68, No. 6
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.6.2972-2981.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.





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