Ouchane S, Picaud M, Vernotte C, Astier C
Centre de G'en'etique Mol'eculaire du Centre National de la Recherche Scientifique (UPR 9061) associ'ee a l'Universit'e Pierre et Marie Curie, Gif sur Yvette, France.
EMBO J. 1997 Aug 1;16(15):4777-87. doi: 10.1093/emboj/16.15.4777.
Carotenoids are essential to protection against photooxidative damage in photosynthetic and non-photosynthetic organisms. In a previous study, we reported the disruption of crtD and crtC carotenoid genes in the purple bacterium Rubrivivax gelatinosus, resulting in mutants that synthesized carotenoid intermediates. Here, carotenoid-less mutants have been constructed by disruption of the crtB gene. To study the biological role of carotenoids in photoprotection, the wild-type and the three carotenoid mutants were grown under different conditions. When exposed to photooxidative stress, only the carotenoid-less strains (crtB-) gave rise with a high frequency to four classes of mutants. In the first class, carotenoid biosynthesis was partially restored. The second class corresponded to photosynthetic-deficient mutants. The third class corresponded to mutants in which the LHI antenna level was decreased. In the fourth class, synthesis of the photosynthetic apparatus was inhibited only in aerobiosis. Molecular analyses indicated that the oxidative stress induced mutations and illegitimate recombination. Illegitimate recombination events produced either functional or non-functional chimeric genes. The R. gelatinosus crtB- strain could be very useful for studies of the SOS response and of illegitimate recombination induced by oxidants in bacteria.
类胡萝卜素对于光合生物和非光合生物抵御光氧化损伤至关重要。在之前的一项研究中，我们报道了在紫色细菌嗜胶红假单胞菌中crtD和crtC类胡萝卜素基因的破坏，导致合成类胡萝卜素中间体的突变体。在此，通过破坏crtB基因构建了无类胡萝卜素突变体。为了研究类胡萝卜素在光保护中的生物学作用，野生型和三种类胡萝卜素突变体在不同条件下生长。当暴露于光氧化应激时，只有无类胡萝卜素菌株（crtB-）高频产生四类突变体。在第一类中，类胡萝卜素生物合成部分恢复。第二类对应于光合缺陷突变体。第三类对应于LHI天线水平降低的突变体。在第四类中，光合装置的合成仅在需氧条件下受到抑制。分子分析表明，氧化应激诱导了突变和非法重组。非法重组事件产生了功能性或非功能性嵌合基因。嗜胶红假单胞菌crtB-菌株对于研究细菌中的SOS反应和氧化剂诱导的非法重组可能非常有用。
