Urea synthesized commercially and formed naturally as a by-product of cellular metab- olism is an important source of nitrogen (N) for primary producers in aquatic ecosystems. Although urea is usually present at ambient concentrations below 1 µM-N, it can contribute 50% or more of the total N used by planktonic communities. Urea may be produced intracellularly via purine catabolism and/or the urea cycle. In many bacteria and eukaryotes, urea in the cell can be broken down by ure- ase into NH4 + and CO2. In addition, some bacteria and eukaryotes use urea amidolyase (UALase) to decompose urea. The regulation of urea uptake appears to differ from the regulation of urease activ- ity, and newly available genomic sequence data reveal that urea transporters in eukaryotic phyto- plankton are distinct from those present in Cyanobacteria and heterotrophic bacteria with different energy sources and possibly different enzyme kinetics. The diverse metabolic pathways of urea transport, production, and decomposition may contribute to differences in the role that urea plays in the physiology and ecology of different species, and in the role that each species plays in the biogeo- chemistry of urea. This review summarizes what is known about urea sources and availability, use of urea as an organic N growth source, rates of urea uptake, enzymes involved in urea metabolism (i.e. urea transporters, urease, UALase), and the biochemical and molecular regulation of urea transport and metabolic enzymes, with an emphasis on the potential for genomic sequence data to continue to provide important new insights.

中文翻译：

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尿素在水生系统微生物代谢中的作用：生化和分子综述

尿素商业合成并作为细胞代谢的副产品自然形成，是水生生态系统初级生产者氮 (N) 的重要来源。尽管尿素通常以低于 1 µM-N 的环境浓度存在，但它可以贡献浮游生物群落使用的总 N 的 50% 或更多。尿素可以通过嘌呤分解代谢和/或尿素循环在细胞内产生。在许多细菌和真核生物中，细胞内的尿素可以被尿素酶分解为 NH4+ 和 CO2。此外，一些细菌和真核生物利用尿素酰胺分解酶（UALase）来分解尿素。尿素摄取的调节似乎与尿素酶活性的调节不同，和新获得的基因组序列数据表明，真核浮游植物中的尿素转运蛋白与蓝藻和异养细菌中存在的那些不同，它们具有不同的能源和可能不同的酶动力学。尿素运输、生产和分解的不同代谢途径可能导致尿素在不同物种的生理和生态中所起的作用不同，以及每个物种在尿素的生物地球化学中所起的作用不同。这篇综述总结了关于尿素来源和可用性、尿素作为有机氮生长源的使用、尿素吸收率、参与尿素代谢的酶（即尿素转运蛋白、尿素酶、UALase）以及尿素的生化和分子调控的已知信息运输和代谢酶，