Evolution from photosynthetic bacteria to cyanobacteria based on carotenoids and carotenogenesis genes

1. 在紫硫菌(2S)-螺旋黄素-2-醇中发现了类胡萝卜素，其部分结构与藻青菌(2S)-粘液醇相似，立体化学结构与藻青菌(2S)-粘液醇相同。已知两种不同的p-胡萝卜素酮酶，CrtO和CrtW。CrtO催化β-胡萝卜素生成棘烯酮，CrtW催化myxol生成酮醇。斑点藻有两种CrtWs，一种为β-胡萝卜素，另一种为黏液醇。紫绿杆菌中的植物烯去饱和酶蓝藻需要三种酶，即CrtP、CrtQ和CrtH将植物烯去饱和转化为番茄红素。Gloeobacter不使用这些酶，而是使用细菌型的CrtI。这个物种是第一个在蓝藻中使用CrtI的例子。对水藻、褐藻和丝状蓝藻等19种蓝藻的类胡萝卜素进行了鉴定。没有鉴定出粘醇糖苷的糖苷部分。它们有独特的类酮胡萝卜素和醇苷。对于胡萝卜素的生成，可能包括番茄红素环化酶、β-胡萝卜素羟化酶（CrtR）、β-胡萝卜素2-羟化酶（crtg样）、β-胡萝卜素酮化酶（CrtO、CrtW）和黏液醇合成酶。各种类胡萝卜素组合物可由于存在或不存在胡萝卜素生成基因和/或酶的底物特异性而产生。这些发现对类胡萝卜素从光合细菌到蓝藻细菌的进化非常有趣。

1. Carotenoids in a novel purple sulfur bacterium(2S)-Spirilloxanthin-2-ol, whose partial structure is similar to that of myxol and stereochemistry is the same with that of (2S)-myxol in cyanobacteria, was identified.2. p-Carotene ketolases in Anabaena sp. PCC 7120Two distinct p-Carotene ketolases, CrtO and CrtW, have been known. CrtO catalyzed β-carotene to echinenone, and CrtW catalyzed myxol to ketomyxol. Nostoc punctiforme have two CrtWs, and the substrate of one is β-carotene, while the other is myxol.3. Phytoene desaturase in Gloeobacter violaseusFor desaturation of phytoene to lycopene, cyanobacteria need three enzymes, CrtP, CrtQ and CrtH. Gloeobacter did not use these enzymes, but used bacterial-type, CrtI. This species is the first example to use CrtI in cyanobacteria.4. Carotenoids in some cyanobacteriaCarotenoids of 19 species including Anabaena, Nostoc and filamentous cyanobacteria, were identified. Glycoside moieties of myxol glycosides were not identified. They had unique ketocarotenoids and myxol glycosides. For carotenogenesis, lycopene cyclase, β-carotene hydroxylase (CrtR), β-carotene 2-hydroxylase (CrtG-like), β-carotene ketolases (CrtO, CrtW) and myxol synthesis enzymes might be included. Various carotenoid compositions may be owing to presence or absence of carotenogenesis gene(s) and/or the substrate specificity of the enzyme(s). These findings are very interesting on the evolution of carotenoids from photosynthetic bacteria to cyanobacteria.