Cobalamin influences marine microbial communities because an exogenous source is required by most eukaryotic phytoplankton, and demand can exceed supply. Pseudocobalamin is a cobalamin analogue produced and used by most cyanobacteria but is not directly available to eukaryotic phytoplankton. Some microbes can remodel pseudocobalamin into cobalamin, but a scarcity of pseudocobalamin measurements impedes our ability to evaluate its importance for marine cobalamin production. Here, we perform simultaneous measurements of pseudocobalamin and methionine synthase (MetH), the key protein that uses it as a co‐factor, in Synechococcus cultures and communities. In Synechococcus sp. WH8102, pseudocobalamin quota decreases in low temperature (17°C) and low nitrogen to phosphorus ratio, while MetH did not. Pseudocobalamin and MetH quotas were influenced by culture methods and growth phase. Despite the variability present in cultures, we found a comparably consistent quota of 300 ± 100 pseudocobalamin molecules per cyanobacterial cell in the Northwest Atlantic Ocean, suggesting that cyanobacterial cell counts may be sufficient to estimate pseudocobalamin inventories in this region. This work offers insights into cellular pseudocobalamin metabolism, environmental and physiological conditions that may influence it, and provides environmental measurements to further our understanding of when and how pseudocobalamin can influence marine microbial communities.

中文翻译：

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伪钴胺素在海洋聚球菌培养物和群落中的生产和利用


钴胺素影响海洋微生物群落，因为大多数真核浮游植物都需要外源来源，并且需求可能超过供应。伪钴胺素是大多数蓝细菌产生和使用的钴胺素类似物，但不能直接用于真核浮游植物。一些微生物可以将假钴胺素重塑为钴胺素，但伪钴胺素测量的稀缺阻碍了我们评估其对海洋钴胺素生产重要性的能力。在这里，我们在聚球菌培养物和群落中同时测量假钴胺素和蛋氨酸合酶 （MetH），这是将其用作辅助因子的关键蛋白质。在 Synechococcus sp. WH8102 中，假钴胺素配额在低温 （17°C） 和低氮磷比下降低，而 MetH 则没有。假钴胺素和 MetH 配额受培养方法和生长期的影响。尽管培养物中存在差异，但我们发现在西北大西洋每个蓝藻细胞 300 ± 100 个假钴胺素分子的配额相对一致，这表明蓝藻细胞计数可能足以估计该地区的假钴胺素库存。这项工作提供了对细胞伪钴胺素代谢、可能影响它的环境和生理条件的见解，并提供了环境测量，以进一步了解伪钴胺素何时以及如何影响海洋微生物群落。