羟基酸乙醇酸盐是环境中高度丰富的碳源。乙醇酸盐由单细胞光合生物产生,并以petram鳞片排泄到环境中,作为异养细菌的生长底物。在微生物代谢中,乙醇酸首先被乙醇酸氧化酶氧化为乙醛酸。最近描述的β-羟基天冬氨酸循环(BHAC)随后介导乙醛酸的碳中和同化进入普遍存在的α-和γ-变形杆菌的中心代谢。尽管BHAC的反应顺序在反硝化副球菌中得到了阐明,在这种相关的α-变形杆菌模型生物中,关于乙醇酸盐和乙醛酸盐同化的调节知之甚少。这里,我们表明,在反硝化假单胞菌中乙醇酸代谢的调节是惊人的复杂,涉及两个监管机构,IclR型转录因子BhcR作为BHAC基因簇的激活剂,和GntR型转录调节因子GlcR,一种以前未知的抑制物质,控制乙醇酸氧化酶的产生。此外,在全球一级实施了额外的监管层,它涉及转录调节因子CceR,它控制脱氮假单胞菌糖酵解和糖异生之间的转换。一起,这些调节剂控制脱氮假单胞菌的乙醇酸代谢,允许生物体同时吸收乙醇酸盐和其他碳底物,而不是顺序。我们的结果表明,α变形菌的代谢网络显示出高度的灵活性,可以对环境中多种底物的可用性作出反应。重要藻类表现大约。我们星球上50%的光合作用二氧化碳固定。在这个过程中,它们释放出二碳分子乙醇酸盐.由于藻类的丰富,大量的乙醇酸盐被释放。因此,这种分子可作为环境中细菌的碳源。这里,我们描述了模型生物反硝化副球菌中乙醇酸代谢的调节。该细菌使用最近表征的β-羟基天冬氨酸循环以碳和能量有效的方式同化乙醇酸盐。我们发现乙醇酸同化受三种不同转录调节因子的动态控制:GlcR,BhcR,还有CceR.这允许脱氮假单胞菌以同时的方式与其他碳底物一起同化乙醇酸盐。总的来说,这种对反硝化假单胞菌中乙醇酸代谢的灵活和多层调节代表了一种资源高效的策略,可以在波动的环境条件下最佳利用这种全球丰富的分子.
The hydroxyacid glycolate is a highly abundant carbon source in the environment. Glycolate is produced by unicellular photosynthetic organisms and excreted at petagram scales to the environment, where it serves as growth substrate for heterotrophic bacteria. In microbial metabolism, glycolate is first oxidized to glyoxylate by the enzyme glycolate oxidase. The recently described β-hydroxyaspartate cycle (BHAC) subsequently mediates the carbon-neutral assimilation of glyoxylate into central metabolism in ubiquitous Alpha- and Gammaproteobacteria. Although the reaction sequence of the BHAC was elucidated in Paracoccus denitrificans, little is known about the regulation of glycolate and glyoxylate assimilation in this relevant alphaproteobacterial model organism. Here, we show that regulation of glycolate metabolism in P. denitrificans is surprisingly complex, involving two regulators, the IclR-type transcription factor BhcR that acts as an activator for the BHAC gene cluster, and the GntR-type transcriptional regulator GlcR, a previously unidentified repressor that controls the production of glycolate oxidase. Furthermore, an additional layer of regulation is exerted at the global level, which involves the transcriptional regulator CceR that controls the switch between glycolysis and gluconeogenesis in P. denitrificans. Together, these regulators control glycolate metabolism in P. denitrificans, allowing the organism to assimilate glycolate together with other carbon substrates in a simultaneous fashion, rather than sequentially. Our results show that the metabolic network of Alphaproteobacteria shows a high degree of flexibility to react to the availability of multiple substrates in the environment.IMPORTANCEAlgae perform ca. 50% of the photosynthetic carbon dioxide fixation on our planet. In the process, they release the two-carbon molecule glycolate. Due to the abundance of algae, massive amounts of glycolate are released. Therefore, this molecule is available as a source of carbon for bacteria in the environment. Here, we describe the regulation of glycolate metabolism in the model organism Paracoccus denitrificans. This bacterium uses the recently characterized β-hydroxyaspartate cycle to assimilate glycolate in a carbon- and energy-efficient manner. We found that glycolate assimilation is dynamically controlled by three different transcriptional regulators: GlcR, BhcR, and CceR. This allows P. denitrificans to assimilate glycolate together with other carbon substrates in a simultaneous fashion. Overall, this flexible and multi-layered regulation of glycolate metabolism in P. denitrificans represents a resource-efficient strategy to make optimal use of this globally abundant molecule under fluctuating environmental conditions.