Daghino Stefania, Martino Elena, Fenoglio Ivana, Tomatis Maura, Perotto Silvia, Fubini Bice
University of Torino, Dipartimento Biologia Vegetale and Center of Excellence for Plant and Microbial Biosensing (CEBIOVEM), viale Mattioli 25, 10125 Torino, Italy.
Chemistry. 2005 Sep 19;11(19):5611-8. doi: 10.1002/chem.200500046.
In a previous study several strains of soil fungi were reported to remove iron in vitro from crocidolite asbestos, a process that was envisaged as a possible bioremediation route for asbestos-polluted soils. Here, we get some new insight into the chemical basis of the fiber/fungi interaction by comparing the action of the most active fungal strain Fusarium oxysporum on three kind of asbestos fibers--chrysotile, amosite, and crocidolite--and on a surface-modified crocidolite. None of the fibers examined significantly inhibited biomass production. Even the smallest fibrils were visibly removed from the supernatant following adhesion to fungal hyphae. F. oxysporum, through release of chelators, extracted iron from all fibers; the higher the amount of iron at the exposed surface, the larger the amount removed, that is, crocidolite > amosite >> chrysotile. When considering the fraction of total iron extracted, however, the ranking was chrysotile > crocidolite > amosite > heated crocidolite, because of the different accessibility of the chelators to the metal ions in the crystal structure. Chrysotile was the easiest to deplete of its metal content. Iron removal fully blunted HO* radical release from crocidolite and chrysotile but only partially from amosite. The removal, in a long-term experiment, of more iron than is expected to be at the surface suggests a diffusion of ions from the bulk solid towards the surface depleted of iron by fungal activity. Thus, if the fibers could be treated with a continuous source of chelators, iron extraction would proceed up to a full inactivation of free radical release. The fungal metabolic response of F. oxysporum grown in the presence of chrysotile, amosite and crocidolite revealed that new extracellular proteins are induced--including manganese-superoxide dismutase, the typical antioxidant defense--and others are repressed, upon direct contact with the fibers. The protein profile induced by heated crocidolite was different, a result suggesting a key role for the state of the fiber/hyphae interface in protein induction.
在之前的一项研究中，据报道几种土壤真菌菌株可在体外从青石棉中去除铁，这一过程被设想为石棉污染土壤可能的生物修复途径。在此，我们通过比较最具活性的真菌菌株尖孢镰刀菌对三种石棉纤维——温石棉、铁石棉和青石棉——以及一种表面改性青石棉的作用，对纤维/真菌相互作用的化学基础有了一些新的认识。所检测的纤维均未显著抑制生物量的产生。即使是最小的纤维原，在附着于真菌菌丝后也能明显地从上清液中去除。尖孢镰刀菌通过释放螯合剂从所有纤维中提取铁；暴露表面的铁含量越高，去除的量就越大，即青石棉>铁石棉>>温石棉。然而，考虑到提取的总铁分数时，排序为温石棉>青石棉>铁石棉>加热后的青石棉，这是因为螯合剂对晶体结构中金属离子的可及性不同。温石棉最容易耗尽其金属含量。铁的去除完全抑制了青石棉和温石棉中HO*自由基的释放，但仅部分抑制了铁石棉中的释放。在一项长期实验中，去除的铁比预期表面的铁更多，这表明离子从块状固体向因真菌活性而铁耗尽的表面扩散。因此，如果纤维能用连续的螯合剂源处理，铁的提取将进行到自由基释放完全失活。在温石棉、铁石棉和青石棉存在的情况下生长的尖孢镰刀菌的真菌代谢反应表明，直接接触纤维后会诱导新的细胞外蛋白质——包括锰超氧化物歧化酶，典型的抗氧化防御蛋白——而其他一些蛋白质则受到抑制。加热后的青石棉诱导的蛋白质谱不同，这一结果表明纤维/菌丝界面状态在蛋白质诱导中起关键作用。
