Huang Jun-Chao, Chen Feng, Sandmann Gerhard
Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China.
J Biotechnol. 2006 Mar 23;122(2):176-85. doi: 10.1016/j.jbiotec.2005.09.002. Epub 2005 Oct 19.
The unicellular green alga Haematococcus pluvialis is used as a biological production system for astaxanthin. It accumulates large amounts of this commercially interesting ketocarotenoid under a variety of environmental stresses. Here we report the identification and expression of three different beta-carotene ketolase genes (bkt) that are involved in the biosynthesis of astaxanthin in a single strain of the alga. Bkt1 and bkt2 proved to be the crtO and bkt previously isolated from two different strains of H. pluvialis. Bkt3 is a novel third gene, which shared 95% identical nucleotide sequence with bkt2. Nitrogen deficiency alone could not induce the alga cells to produce astaxanthin in 3 days even though it enhances the expression of the bkt genes to three times of that in normal growing cells within 16 h. High light irradiation (125 micromol m(-2)s(-1)) or 45 mM sodium acetate greatly increased the expression of bkt genes to 18 or 52 times of that in normal growing cells, resulting in an accumulation of substantial astaxanthin (about 6 mg g(-1) dry biomass) in 3 days. It is suggested that the existence of the multiple bkt genes and their strong up-regulation by different stress conditions is one of the reasons that H. pluvialis accumulates large amounts of astaxanthin in an instant response to stress environments.
单细胞绿藻雨生红球藻被用作虾青素的生物生产系统。在多种环境胁迫下，它会积累大量这种具有商业价值的酮类胡萝卜素。在此，我们报告了在该藻类的一个单一菌株中参与虾青素生物合成的三种不同的β - 胡萝卜素酮酶基因（bkt）的鉴定和表达。结果证明，Bkt1和bkt2分别是先前从雨生红球藻的两个不同菌株中分离得到的crtO和bkt。Bkt3是一个新的第三个基因，其与bkt2的核苷酸序列有95%的同一性。单独的氮缺乏在3天内无法诱导藻类细胞产生虾青素，尽管它能在16小时内将bkt基因的表达增强至正常生长细胞中的三倍。高光照射（125 μmol m(-2)s(-1)）或45 mM醋酸钠可使bkt基因的表达大幅增加至正常生长细胞中的18倍或52倍，从而在3天内积累大量虾青素（约6 mg g(-1)干生物量）。这表明多个bkt基因的存在及其在不同胁迫条件下的强烈上调是雨生红球藻在应激环境中能迅速积累大量虾青素的原因之一。
