Brzezinski Mark A, Krause Jeffrey W, Baines Stephen B, Collier Jackie L, Ohnemus Daniel C, Twining Benjamin S
Marine Science Institute and the Department of Ecology Evolution and Marine Biology, University of California, Santa Barbara, California, USA.
Dauphin Island Sea Lab, Dauphin Island, Alabama, USA.
J Phycol. 2017 Aug;53(4):746-761. doi: 10.1111/jpy.12545. Epub 2017 May 23.
Six clones of the marine cyanobacterium Synechococcus, representing four major clades, were all found to contain significant amounts of silicon in culture. Growth rate was unaffected by silicic acid, Si(OH) , concentration between 1 and 120 μM suggesting that Synechococcus lacks an obligate need for silicon (Si). Strains contained two major pools of Si: an aqueous soluble and an aqueous insoluble pool. Soluble pool sizes correspond to estimated intracellular dissolved Si concentrations of 2-24 mM, which would be thermodynamically unstable implying the binding of intracellular soluble Si to organic ligands. The Si content of all clones was inversely related to growth rate and increased with higher [Si(OH) ] in the growth medium. Accumulation rates showed a unique bilinear response to increasing [Si(OH) ] from 1 to 500 μM with the rate of Si acquisition increasing abruptly between 80 and 100 μM Si(OH) . Although these linear responses imply some form of diffusion-mediated transport, Si uptake rates at low Si (~1 μM Si) were inhibited by orthophosphate, suggesting a role of phosphate transporters in Si acquisition. Theoretical calculations imply that observed Si acquisition rates are too rapid to be supported by lipid-solubility diffusion of Si through the plasmalemma; however, facilitated diffusion involving membrane protein channels may suffice. The data are used to construct a working model of the mechanisms governing the Si content and rate of Si acquisition in Synechococcus.
海洋蓝藻聚球藻的六个克隆代表四个主要进化枝，在培养物中均被发现含有大量硅。硅酸（Si(OH)₄）浓度在1至120 μM之间时，生长速率不受影响，这表明聚球藻对硅（Si）没有绝对需求。菌株含有两个主要的硅库：水溶态和水不溶态库。水溶态库的大小对应于估计的细胞内溶解硅浓度为2 - 24 mM，这在热力学上是不稳定的，意味着细胞内可溶性硅与有机配体结合。所有克隆的硅含量与生长速率呈负相关，并随着生长培养基中[Si(OH)₄]的升高而增加。积累速率对[Si(OH)₄]从1增加到500 μM呈现独特的双线性响应，硅摄取速率在80至100 μM Si(OH)₄之间突然增加。尽管这些线性响应意味着某种形式的扩散介导运输，但低硅（约1 μM Si）时的硅摄取速率受到正磷酸盐的抑制，表明磷酸盐转运体在硅摄取中起作用。理论计算表明，观察到的硅摄取速率太快，无法由硅通过质膜的脂溶性扩散来支持；然而，涉及膜蛋白通道的易化扩散可能足够。这些数据用于构建一个关于聚球藻中硅含量和硅摄取速率调控机制的工作模型。
