Veaudor Théo, Cassier-Chauvat Corinne, Chauvat Franck
Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France.
Front Microbiol. 2019 Sep 4;10:2052. doi: 10.3389/fmicb.2019.02052. eCollection 2019.
Cyanobacteria are widely-diverse prokaryotes that colonize our planet. They use solar energy to assimilate huge amounts of atmospheric CO and produce a large part of the biomass and oxygen that sustain most life forms. Cyanobacteria are therefore increasingly studied for basic research objectives, as well as for the photosynthetic production of chemicals with industrial interests. One potential approach to reduce the cost of future bioproduction processes is to couple them with wastewater treatment, often polluted with urea, which in any case is cheaper than nitrate. As of yet, however, research has mostly focused on a very small number of model cyanobacteria growing on nitrate. Thus, the genetic inventory of the cyanobacterial phylum is still insufficiently employed to meaningfully select the right host for the right purpose. This review reports what is known about urea transport and catabolism in cyanobacteria, and what can be inferred from the comparative analysis of the publicly available genome sequence of the 308 cyanobacteria. We found that most cyanobacteria mostly harbor the genes encoding the urea catabolytic enzymes urease (), but not systematically, together with the urea transport (). These findings are consistent with the capacity of the few tested cyanobacteria that grow on urea as the sole nitrogen source. They also indicate that urease is important for the detoxification of internally generated urea (re-cycling its carbon and nitrogen). In contrast, several cyanobacteria have but not , suggesting that could operate in the transport of not only urea but also of other nutrients. Only four cyanobacteria appeared to have the genes encoding the urea carboxylase () and allophanate hydrolase () enzymes that sequentially catabolize urea. Three of these cyanobacteria belongs to the genera Gloeobacter and Gloeomargarita that have likely diverged early from other cyanobacteria, suggesting that the urea carboxylase and allophanate hydrolase enzymes appeared in cyanobacteria before urease.
蓝藻是广泛分布的原核生物，遍布我们的星球。它们利用太阳能同化大量大气中的二氧化碳，并产生维持大多数生命形式所需的大部分生物质和氧气。因此，蓝藻越来越多地被用于基础研究目的，以及光合生产具有工业价值的化学品。降低未来生物生产过程成本的一种潜在方法是将其与废水处理相结合，废水中通常含有尿素，而尿素无论如何都比硝酸盐便宜。然而，到目前为止，研究主要集中在极少数以硝酸盐为生长底物的模式蓝藻上。因此，蓝藻门的基因库仍未得到充分利用，无法有意义地为特定目的选择合适的宿主。本综述报告了关于蓝藻中尿素转运和分解代谢的已知信息，以及从对308种蓝藻公开可用基因组序列的比较分析中可以推断出的信息。我们发现，大多数蓝藻大多含有编码尿素分解代谢酶脲酶（）的基因，但并非系统地与尿素转运（）基因一起存在。这些发现与少数以尿素作为唯一氮源生长的经过测试的蓝藻的能力一致。它们还表明脲酶对于内源性产生的尿素的解毒（循环利用其碳和氮）很重要。相比之下，几种蓝藻有 但没有 ，这表明 不仅可以转运尿素，还可以转运其他营养物质。只有四种蓝藻似乎具有编码依次分解尿素的尿素羧化酶（）和脲基甲酸水解酶（）的基因。其中三种蓝藻属于Gloeobacter属和Gloeomargarita属，它们可能在早期就与其他蓝藻分化，这表明尿素羧化酶和脲基甲酸水解酶在蓝藻中出现的时间早于脲酶。
