School of Oceanography, University of Washington, Seattle, Washington, United States of America.
PLoS One. 2021 Mar 24;16(3):e0241960. doi: 10.1371/journal.pone.0241960. eCollection 2021.
Diatoms are unicellular photosynthetic algae known to secrete organic matter that fuels secondary production in the ocean, though our knowledge of how their physiology impacts the composition of dissolved organic matter remains limited. Like all photosynthetic organisms, their use of light for energy and reducing power creates the challenge of avoiding cellular damage. To better understand the interplay between redox balance and organic matter secretion, we reconstructed a genome-scale metabolic model of Thalassiosira pseudonana strain CCMP 1335, a model for diatom molecular biology and physiology, with a 60-year history of studies. The model simulates the metabolic activities of 1,432 genes via a network of 2,792 metabolites produced through 6,079 reactions distributed across six subcellular compartments. Growth was simulated under different steady-state light conditions (5-200 μmol photons m-2 s-1) and in a batch culture progressing from exponential growth to nitrate-limitation and nitrogen-starvation. We used the model to examine the dissipation of reductants generated through light-dependent processes and found that when available, nitrate assimilation is an important means of dissipating reductants in the plastid; under nitrate-limiting conditions, sulfate assimilation plays a similar role. The use of either nitrate or sulfate uptake to balance redox reactions leads to the secretion of distinct organic nitrogen and sulfur compounds. Such compounds can be accessed by bacteria in the surface ocean. The model of the diatom Thalassiosira pseudonana provides a mechanistic explanation for the production of ecologically and climatologically relevant compounds that may serve as the basis for intricate, cross-kingdom microbial networks. Diatom metabolism has an important influence on global biogeochemistry; metabolic models of marine microorganisms link genes to ecosystems and may be key to integrating molecular data with models of ocean biogeochemistry.
硅藻是一种单细胞光合藻类，已知其能分泌有机物质，为海洋中的次级生产提供燃料，但我们对其生理学如何影响溶解有机物质的组成知之甚少。与所有光合生物一样，它们利用光来获取能量和还原力，这就带来了避免细胞损伤的挑战。为了更好地理解氧化还原平衡和有机物质分泌之间的相互作用，我们重建了一株模式硅藻——秀丽隐杆藻 CCMP 1335 的基因组规模代谢模型，该藻是硅藻分子生物学和生理学的模式生物，已有 60 年的研究历史。该模型通过一个由 2792 种代谢物组成的网络模拟了 1432 个基因的代谢活动，这些代谢物通过 6079 个反应产生，分布在 6 个亚细胞隔室中。在不同的稳态光照条件（5-200 μmol 光子 m-2 s-1）和从指数增长到硝酸盐限制和氮饥饿的分批培养中模拟了生长。我们利用该模型研究了通过依赖光的过程产生的还原剂的耗散情况，发现当硝酸盐可用时，硝酸盐同化是在质体中耗散还原剂的重要途径；在硝酸盐限制条件下，硫酸盐同化也起着类似的作用。利用硝酸盐或硫酸盐的摄取来平衡氧化还原反应会导致不同的有机氮和硫化合物的分泌。这些化合物可以被海洋表面的细菌利用。模式硅藻秀丽隐杆藻的模型为生产具有生态和气候相关性的化合物提供了一种机制解释，这些化合物可能成为复杂的跨领域微生物网络的基础。硅藻代谢对全球生物地球化学有重要影响；海洋微生物的代谢模型将基因与生态系统联系起来，可能是将分子数据与海洋生物地球化学模型整合的关键。
