Every living cell is composed of macromolecules such as proteins, DNA, RNA, and pigments. The ratio between these macromolecular pools depends on the allocation of resources within the organism to different physiological requirements, and in turn affects biogeochemical cycles of elements such as carbon, nitrogen, and phosphorus. Here, we present detailed measurements of the macromolecular composition of Prochlorococcus MIT9312, a representative strain of a globally abundant marine primary producer, as it grows and declines due to nitrogen starvation in laboratory batch cultures. As cells reached stationary stage and declined, protein per cell decreased by ~ 30% whereas RNA per cell and pigments per cell decreased by ~ 75%. The decline stage was associated with the appearance of chlorotic cells, which had higher forward scatter (a proxy for cell size) but lower chlorophyll autofluorescence, as well as with changes in photosynthetic pigment composition. Specifically, during culture decline divinyl-chlorophyll-like pigments emerged, which were not observed during exponential growth. These divinyl-chlorophyll-like pigments were also observed in natural samples from the Eastern Mediterranean. Over 90% of the carbon fixed by Prochlorococcus MIT9312 (but not of a different strain, NATL2A) was released into the growth media under these laboratory conditions. Variations in RNA/protein indicate that, broadly defined, the macromolecular composition of Prochlorococcus MIT9312 is more similar to eukaryotic phytoplankton than to marine heterotrophic bacteria, possibly due to the significant investment in photosynthetic machinery of phototrophs.

中文翻译：

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原球菌中的动态大分子组成和高渗出率

每个活细胞都由大分子组成，例如蛋白质，DNA，RNA和色素。这些大分子库之间的比率取决于生物体内资源对不同生理需求的分配，进而影响诸如碳，氮和磷等元素的生物地球化学循环。在这里，我们提出了Prochlorococcus大分子组成的详细测量MIT9312是全球丰富的海洋初级生产者的代表菌株，由于实验室分批培养中的氮缺乏而使其生长和下降。随着细胞达到稳定期并下降，每个细胞的蛋白质减少约30％，而每个细胞的RNA和每个细胞的色素减少约75％。下降阶段与叶绿素细胞的出现有关，后者具有较高的前向散射（代表细胞大小），但叶绿素的自发荧光较低，并且与光合色素成分的变化有关。具体而言，在培养过程中出现二乙烯基叶绿素样色素下降，这在指数生长过程中未观察到。这些二乙烯基叶绿素样颜料还出现在来自地中海东部的天然样品中。原球菌固定的碳超过90％在这些实验室条件下，MIT9312（但不是另一种菌株，NATL2A）被释放到生长培养基中。RNA /蛋白质的变化表明，广义上来说，原球菌MIT9312的大分子组成与真核浮游植物比海洋异养细菌更相似，这可能是由于对光养生物的光合机制进行了大量投资。