Department of Botany and Plant Biology, Microbiology Unit, University of Geneva, Sciences III, Geneva, Switzerland.
FEMS Microbiol Ecol. 2013 May;84(2):421-32. doi: 10.1111/1574-6941.12074. Epub 2013 Feb 11.
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.
卡达戈湖的特征是一个紧凑的化变层，其中含有高浓度的各种光养硫细菌。在原位实验中，我们将代表化变层中数量最多的四个种群的四个菌株放入透析袋中，以测试它们固定 CO₂ 的能力。在测试的四个菌株中，紫色硫细菌候选种“Thiodictyon syntrophicum”菌株 Cad16(T) 的 CO₂同化率最高，即使在黑暗中也具有很高的 CO₂同化率。Cad16(T) 菌株所代表的种群的 CO₂同化量估计占化变层中总初级生产力的 25%。暴露在 12 小时光照和 12 小时黑暗周期下的 Cad16(T) 纯培养物在光照的前 4 小时表现出最高的 CO₂同化率。Cad16(T) 的草图基因组序列显示存在 cbbL 和 cbbM 基因，分别编码 RuBisCO 的 I 型和 II 型。转录分析证实，尽管 cbbM 在光照和黑暗暴露期间表达水平较低，但 cbbL 的表达在光暗周期中发生变化，并受到可用碳源的影响。有趣的是，cbbL 表达的峰值与 CO₂同化的峰值并不相关。
