Australian Water Quality Centre, South Australian Water Corporation, 250 Victoria Square, Adelaide, South Australia 5000, Australia.
Environ Sci Technol. 2011 Feb 1;45(3):992-8. doi: 10.1021/es102992p. Epub 2010 Dec 21.
The production of odiferous metabolites, such as 2-methlyisoborneol (MIB), is a major concern for water utilities worldwide. Although MIB has no known biological function, the presence of the earthy/musty taste and odor attributed to this compound result in the reporting of numerous complaints by consumers, which undermines water utility performance and the safe and adequate provision of potable waters. Cyanobacteria are the major producers of MIB in natural waters, by mechanisms that have heretofore remained largely unstudied. To investigate the fundamental biological mechanism of MIB biosynthesis in cyanobacteria, the genome of a MIB-producing Pseudanabaena limnetica was sequenced using Next Generation Sequencing, and the recombinant proteins derived from the putative MIB biosynthetic genes were biochemically characterized. We demonstrate that the biosynthesis of MIB in cyanobacteria is a result of 2 key reactions: 1) a S-adenosylmethionine-dependent methylation of the monoterpene precursor geranyl diphosphate (GPP) to 2-methyl-GPP catalyzed by geranyl diphosphate 2-methyltransferase (GPPMT) and 2) further cyclization of 2-methyl-GPP to MIB catalyzed by MIB synthase (MIBS) as part of a MIB operon. Based on a comparison of the component MIB biosynthetic genes in actinomycetes and cyanobacterial organisms, we hypothesize that there have been multiple rearrangements of the genes in this operon.
产生有气味的代谢物，如 2-甲基异莰醇（MIB），是全球水务公司的主要关注点。虽然 MIB 没有已知的生物学功能，但由于这种化合物具有土腥味和霉味，导致消费者报告了大量投诉，从而破坏了水务公司的绩效以及安全和充足的饮用水供应。蓝藻是天然水中 MIB 的主要生产者，其产生机制迄今仍在很大程度上未被研究。为了研究蓝藻中 MIB 生物合成的基本生物学机制，我们使用下一代测序技术对产生 MIB 的拟鱼腥藻（Pseudanabaena limnetica）的基因组进行了测序，并对来自假定的 MIB 生物合成基因的重组蛋白进行了生化特性分析。我们证明，蓝藻中 MIB 的生物合成是 2 个关键反应的结果：1）依赖 S-腺苷甲硫氨酸的单萜前体香叶基二磷酸（GPP）的甲基化反应，由香叶基二磷酸 2-甲基转移酶（GPPMT）催化，生成 2-甲基-GPP；2）2-甲基-GPP 在 MIB 合酶（MIBS）的作用下进一步环化生成 MIB，该酶是 MIB 操纵子的一部分。通过比较放线菌和蓝藻生物中 MIB 生物合成基因的成分，我们假设该操纵子中的基因发生了多次重排。
