title: CO₂ assimilation in the chemocline of Lake Cadagno is dominated by a few types of phototrophic purple sulfur bacteria.
abstract: Lake Cadagno is characterized by a compact chemocline that harbors high concentrations of various phototrophic sulfur bacteria. Four strains representing the numerically most abundant populations in the chemocline were tested in dialysis bags in situ for their ability to fix CO₂. The purple sulfur bacterium Candidatus 'Thiodictyon syntrophicum' strain Cad16(T) had the highest CO₂ assimilation rate in the light of the four strains tested and had a high CO₂ assimilation rate even in the dark. The CO₂ assimilation of the population represented by strain Cad16(T) was estimated to be up to 25% of the total primary production in the chemocline. Pure cultures of strain Cad16(T) exposed to cycles of 12 h of light and 12 h of darkness exhibited the highest CO₂ assimilation during the first 4 h of light. The draft genome sequence of Cad16(T) showed the presence of cbbL and cbbM genes, which encode form I and form II of RuBisCO, respectively. Transcription analyses confirmed that, whereas cbbM remained poorly expressed throughout light and dark exposure, cbbL expression varied during the light-dark cycle and was affected by the available carbon sources. Interestingly, the peaks in cbbL expression did not correlate with the peaks in CO₂ assimilation.
authors: Department of Botany and Plant Biology, Microbiology Unit, University of Geneva, Sciences III, Geneva, Switzerland.
authors: Nicola
authors: N
authors: Storelli
authors: Sandro
authors: S
authors: Peduzzi
authors: Maged M
authors: MM
authors: Saad
authors: Niels-Ulrik
authors: NU
authors: Frigaard
authors: Xavier
authors: X
authors: Perret
authors: Mauro
authors: M
authors: Tonolla
mesh_terms: D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D002841:Chromatiaceae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D060106:Lakes / Q000737:chemistry / Q000382:microbiology*; D017440:Photoperiod; D052817:Phototrophic Processes; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics
chemical_list: D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase