The ecological niche of the consortium " Pelochromatium roseum "

Abstract

A dense accumulation of the phototrophic consortium "Pelochromatium roseum" in a small, eutrophic, freshwater lake (Dagowsee, Brandenburg, Germany) was investigated. Within the chemocline, the number of epibionts of the consortia represented up to 19% of the total number of bacteria. Per "P. roseum" a mean value of 20 epibionts was determined. Similar to other aquatic habitats, consortia in the Dagowsee were found only at low light intensities (< 7 &mgr;mol quanta m-2 s-1) and low sulfide concentrations (0-100 &mgr;M). In dialysis cultures of "P. roseum", bacterial cells remained in a stable association only when incubated at light intensities between 5 and 10 &mgr;mol quanta m-2 s-1. Intact consortia from natural samples had a buoyant density of 1046.8 kg m-3, which was much higher than that of ambient chemocline water (995.8 kg m-3). Under environmental conditions and without motility, this density difference would result in rapid sedimentation of consortia toward the lake bottom. Our results indicate that (1) consortia are adapted to a very narrow regime of light intensities and sulfide concentrations, (2) motility and tactic responses must be of ecological significance for the colonization of the free water column of lakes, and (3) phototrophic growth of consortia can be explained only by a cycling of sulfur species in the chemocline, possibly within the consortia themselves.

Metabolic analysis of Chlorobium chlorochromatii CaD3 reveals clues of the symbiosis in ‘Chlorochromatium aggregatum’

“…aggregatum' shows chemotactic behavior towards 2-oxoglutarate (Frö stl . Several lines of evidence suggest that the b-proteobacterium and not the chlorobia, assimilates this metabolite from the medium (Frö stl and Overmann et al, 1998;Glaeser and Overmann, 2003b;Vogl et al, 2006). However, it is not known whether the central bacterium transfers organic carbon to the epibiont (Mü ller and Overmann, 2011).…”

Metabolic integration during the evolutionary origin of mitochondria

“…The consortium consists of a large central non-photosynthetic cell, now known to be a -Proteobacterium, surrounded by about a dozen photosynthetic green sulfur bacteria [28]. This and similar consortia involving photosynthetic sulfur bacteria are highly successful, and occur worldwide in ponds that contain a lower H 2 S-rich layer [42]. It has been questioned whether H 2 S is transferred directly from species to species [43], but since the outer bacteria are obligate H 2 S consumers, sulfide oxidation is certainly involved.…”

Characterization and In Situ Carbon Metabolism of Phototrophic Consortia

“…In motile phototrophic consortia, numerous green sulfur bacteria (so-called epibionts) are attached around a single, flagellated, colorless cell of a member of the ␤ subclass of the Proteobacteria, thereby forming a barrel-shaped highly regular structure (14,15,37). Motile phototrophic consortia were first described in the early 20th century (7,27) and since then have been detected in numerous stratified freshwater lakes and ponds worldwide (40). To date, seven different types of motile phototrophic consortia have been distinguished on the basis of color, size, and shape and on the basis of the number and morphology of the epibionts (41).…”

“…Phototrophic consortia can contribute up to two-thirds of the total bacterial biomass in the chemoclines of stagnant water bodies (17) and therefore are significant for the biogeochemical cycles in these environments (40). However, epibionts of motile phototrophic consortia represent unique phylotypes among the green sulfur bacteria (15) and therefore may differ in physiology from their free-living relatives.…”

“…However, in situ measurements for a natural community of the phototrophic consortium "Pelochromatium roseum" revealed that the vertical diffusive flux of hydrogen sulfide was not sufficient to explain the large biomass of consortia present in the chemocline (40). Sulfide could be produced within the phototrophic consortium population, either by the central bacterium in each consortium or by accompanying bacteria outside the consortium (40).…”