Juarez Angela Beatriz, Barsanti Laura, Passarelli Vincenzo, Evangelista Valter, Vesentini Nicoletta, Conforti Visitacion, Gualtieri Paolo
Departimento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, C1428EHA, Buenos Aires, Argentina.
J Environ Monit. 2008 Nov;10(11):1313-8. doi: 10.1039/b809566c. Epub 2008 Sep 18.
In microorganisms and plants, chromium (Cr) is not essential for any metabolic process, and can ultimately prove highly deleterious. Due to its widespread industrial use, chromium has become a serious pollutant in diverse environmental settings. The presence of Cr leads to the selection of specific algal populations able to tolerate high levels of Cr compounds. The varying Cr-resistance mechanisms displayed by microorganisms include biosorption, diminished accumulation, precipitation, reduction of Cr(6+) to Cr(3+), and chromate efflux. In this paper we describe the effects of Cr(6+) (the most toxic species) on the photosynthetic and photoreceptive apparatus of two fresh water microalgae, Eudorina unicocca and Chlorella kessleri. We measured the effect of this heavy metal by means of in vivo absorption microspectroscopy of both the thylakoid compartments and the eyespot. The decomposition of the overall absorption spectra in pigment constituents indicates that Cr(6+) effects are very different in the two algae. In E. unicocca the metal induced a complete pheophinitization of the chlorophylls and a modification of the carotenoids present in the eyespot after only 120 h of exposition at a concentration equal or greater than 40 microM, which is the limit for total Cr discharge established by US EPA regulations. In C. kessleri, chromium concentrations a hundred times higher than this limit had no effect on the photosynthetic machinery. The different tolerance level of the two algae is suggested to be due to the different properties of the mucilaginous envelope and cell wall covering, respectively, the colonies of Eudorina and the single cells of Chlorella, which binds chromium cations to a different extent.
在微生物和植物中，铬（Cr）对任何代谢过程都不是必需的，最终可能证明具有高度危害性。由于其在工业上的广泛应用，铬已成为各种环境中的严重污染物。铬的存在导致能够耐受高浓度铬化合物的特定藻类种群的选择。微生物表现出的不同抗铬机制包括生物吸附、积累减少、沉淀、将Cr(6+)还原为Cr(3+)以及铬酸盐外流。在本文中，我们描述了Cr(6+)（毒性最大的物种）对两种淡水微藻——单球团藻（Eudorina unicocca）和凯氏小球藻（Chlorella kessleri）的光合和光感受装置的影响。我们通过对类囊体区室和眼点进行体内吸收光谱测量来测定这种重金属的影响。色素成分中总吸收光谱的分解表明，Cr(6+)对两种藻类的影响非常不同。在单球团藻中，在浓度等于或大于40微摩尔的情况下暴露仅120小时后，这种金属就导致叶绿素完全脱镁，并改变了眼点中存在的类胡萝卜素，这一浓度是美国环境保护局（US EPA）规定的总铬排放限值。在凯氏小球藻中，比这个限值高一百倍的铬浓度对光合机制没有影响。两种藻类不同的耐受水平被认为是由于分别覆盖单球团藻群体和小球藻单细胞的黏液包膜和细胞壁具有不同特性，它们对铬阳离子的结合程度不同。
