德国马克斯·普朗克陆地微生物研究所Tobias J. Erb和Lennart Schada von Borzyskowski团队合作发现海洋变形杆菌通过β-羟基天冬氨酸循环代谢乙醇酸。11月13日，国际学术期刊《自然》在线发表了这一成果。
研究人员发现海洋中普遍存在的变形杆菌能够通过β-羟基天冬氨酸循环（BHAC）吸收乙醛酸。BHAC是在56年前第一次被提出。研究人员阐明了BHAC的生物化学特性，并解析了其关键酶的结构，包括以前未知的主要亚胺还原酶。总体而言，BHAC只需四个酶促反应即可将乙醛酸酯催化生产草酰乙酸，据研究人员介绍，这是迄今为止揭示的最有效的乙醛酸酯同化途径。海洋基因组分析表明，BHAC是全球分布的，平均丰富程度比甘油酸途径高出20倍，后者是唯一已知的主要乙醛酸同化途径。在浮游植物开花的研究中，研究人员发现乙醇酸以高纳摩尔浓度存在，并被原核生物吸收，其吸收速率可在一周之内使乙醇酸池完全转化。在开花期间，编码BHAC关键酶的基因在细菌群落的存在量可达1.5％并被主动转录，从而支持BHAC在乙醇酸同化中的作用，这暗示了自养性浮游植物与异养性浮游植物之间先前未知的营养相互作用。
据悉，乙醇酸是海洋中最丰富的有机碳来源之一，海洋浮游植物每年分泌产生的乙醇酸约占海洋环境中1毫克的乙醇酸通量。尽管普遍认为乙醇酸被海洋细菌氧化为乙醛酸，但人们对这种C2代谢产物的进一步代谢命运知之甚少。
附：英文原文
Title: Marine Proteobacteria metabolize glycolate via the β-hydroxyaspartate cycle
Author: Lennart Schada von Borzyskowski, Francesca Severi, Karen Krger, Lucas Hermann, Alexandre Gilardet, Felix Sippel, Bianca Pommerenke, Peter Claus, Nia Socorro Cortina, Timo Glatter, Stefan Zauner, Jan Zarzycki, Bernhard M. Fuchs, Erhard Bremer, Uwe G. Maier, Rudolf I. Amann, Tobias J. Erb
Issue&Volume: 2019-11-13
Abstract: One of the most abundant sources of organic carbon in the ocean is glycolate, the secretion of which by marine phytoplankton results in an estimated annual flux of one petagram of glycolate in marine environments1. Although it is generally accepted that glycolate is oxidized to glyoxylate by marine bacteria2,3,4, the further fate of this C2 metabolite is not well understood. Here we show that ubiquitous marine Proteobacteria are able to assimilate glyoxylate via the β-hydroxyaspartate cycle (BHAC) that was originally proposed 56 years ago5. We elucidate the biochemistry of the BHAC and describe the structure of its key enzymes, including a previously unknown primary imine reductase. Overall, the BHAC enables the direct production of oxaloacetate from glyoxylate through only four enzymatic steps, representing—to our knowledge—the most efficient glyoxylate assimilation route described to date. Analysis of marine metagenomes shows that the BHAC is globally distributed and on average 20-fold more abundant than the glycerate pathway, the only other known pathway for net glyoxylate assimilation. In a field study of a phytoplankton bloom, we show that glycolate is present in high nanomolar concentrations and taken up by prokaryotes at rates that allow a full turnover of the glycolate pool within one week. During the bloom, genes that encode BHAC key enzymes are present in up to 1.5% of the bacterial community and actively transcribed, supporting the role of the BHAC in glycolate assimilation and suggesting a previously undescribed trophic interaction between autotrophic phytoplankton and heterotrophic bacterioplankton.
DOI: 10.1038/s41586-019-1748-4
Source: https://www.nature.com/articles/s41586-019-1748-4
Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
投稿链接：http://www.nature.com/authors/submit_manuscript.html
本期文章：《自然》：Online/在线发表
