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首页> 外文期刊>Applied and Environmental Microbiology >CO2 Uptake and Fixation by Endosymbiotic Chemoautotrophs from the Bivalve Solemya velum
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CO2 Uptake and Fixation by Endosymbiotic Chemoautotrophs from the Bivalve Solemya velum

机译：Bivalve Solemya膜的内生共生化学自养菌吸收和固定CO2。

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Chemoautotrophic symbioses, in which endosymbiotic bacteria are the major source of organic carbon for the host, are found in marine habitats where sulfide and oxygen coexist. The purpose of this study was to determine the influence of pH, alternate sulfur sources, and electron acceptors on carbon fixation and to investigate which form(s) of inorganic carbon is taken up and fixed by the gamma-proteobacterial endosymbionts of the protobranch bivalve Solemya velum. Symbiont-enriched suspensions were generated by homogenization of S. velum gills, followed by velocity centrifugation to pellet the symbiont cells. Carbon fixation was measured by incubating the cells with 14C-labeled dissolved inorganic carbon. When oxygen was present, both sulfide and thiosulfate stimulated carbon fixation; however, elevated levels of either sulfide (>0.5 mM) or oxygen (1 mM) were inhibitory. In the absence of oxygen, nitrate did not enhance carbon fixation rates when sulfide was present. Symbionts fixed carbon most rapidly between pH 7.5 and 8.5. Under optimal pH, sulfide, and oxygen conditions, symbiont carbon fixation rates correlated with the concentrations of extracellular CO2 and not with HCO3? concentrations. The half-saturation constant for carbon fixation with respect to extracellular dissolved CO2 was 28 ± 3 μM, and the average maximal velocity was 50.8 ± 7.1 μmol min?1 g of protein?1. The reliance of S. velum symbionts on extracellular CO2 is consistent with their intracellular lifestyle, since HCO3? utilization would require protein-mediated transport across the bacteriocyte membrane, perisymbiont vacuole membrane, and symbiont outer and inner membranes. The use of CO2 may be a general trait shared with many symbioses with an intracellular chemoautotrophic partner.
机译：在共生硫化物和氧气的海洋生境中发现了化学自养共生体，其中共生细菌是宿主有机碳的主要来源。这项研究的目的是确定pH值，备用硫源和电子受体对碳固定的影响，并研究原分支双壳类Solemya的γ-蛋白细菌内共生体吸收并固定了哪种形式的无机碳。面纱富集共生体的悬浮液是通过均质化S. velum ill，然后进行速度离心沉淀共生体细胞而产生的。通过将细胞与14C标记的溶解的无机碳一起孵育来测定碳固定。当存在氧时，硫化物和硫代硫酸盐都可以刺激碳的固定。然而，硫化物（> 0.5 mM）或氧气（1 mM）的升高水平具有抑制作用。在没有氧气的情况下，当存在硫化物时，硝酸盐不会提高固碳速率。共混物在pH 7.5和8.5之间固定碳最快。在最佳的pH，硫化物和氧气条件下，共生体的固碳率与细胞外CO2浓度相关，而与HCO3不相关。浓度。相对于细胞外溶解的二氧化碳，碳固定的半饱和常数为28±3μM，平均最大速度为50.8±7.1μmolmin？1 g蛋白质？1。由于HCO3？，S。velum共生体对细胞外CO2的依赖性与其细胞内生活方式相一致。为了利用，将需要蛋白质介导的穿过细菌细胞膜，共生液泡膜以及共生外膜和内膜的转运。使用CO2可能是许多共生酶与细胞内化学自养伴侣共有的一般性状。

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