Physical and biochemical interactions of soil fungi with asbestos fibers

Abstract

Iron, a structural component of most asbestos, is thought to play a crucial role in asbestos toxicity. Surface iron favors fiber uptake by mammalian cells and promotes the generation of free radicals with consequent DNA and lipid damage. In some cases, chemical removal of iron from asbestos fibers has reduced several cellular responses to asbestos. Since iron represents an essential element for soil microorganisms, many of them have developed mechanisms to scavenge this element from poorly soluble forms. We have investigated the ability of some soil fungi to produce iron chelators capable of extracting iron from crocidolite (blue asbestos). Many of the species/isolates investigated could remove significant amounts of iron from crocidolite fibers, Fusarium oxysporum being the most effective. The fungal responses following exposure to asbestos fibers also have been investigated with morphological and biochemical approaches. In liquid cultures, the fibers were visibly cleared from the suspension because they were tightly bound to the fungal hyphae. Modifications in the fungal protein profiles were observed following exposure to asbestos fibers. By binding the fibers and depriving them of iron, selected species/strains of soil fungi might represent interesting tools for the bioremediation of asbestos-contaminated soils.

Inorganic Materials and Living Organisms: Surface Modifications and Fungal Responses to Various Asbestos Forms

“…Previous ultrastructural studies have shown that the fibrils are, in this case, in intimate contact with the fungus. [24,25] None of the fibers examined significantly inhibited biomass production of F. oxysporum grown in liquid culture (Figure 1), either in direct contact with the fungus or when kept in a separate chamber by a dialysis membrane. The presence of asbestos fibers, however, caused the release of a dark yellow soluble pigment in the culture medium.…”

“…[2,16,17,36,37] Biochemical response of fungi to asbestos fibers: Modification in protein expression: The modification in protein expression following interaction with asbestos may be a fungal response either to physical contact with the fibers or to a possible oxidative stress caused by the fiber or by mobilized iron. The SEM analysis of mycelia grown in direct contact with the fibers showed the physical integrity of hyphae; [25] thus, the extracellular protein pool changes in the presence of fibers are likely to be due to active synthesis. Protein induction or inhibition due to stress is reported in several studies on fungi and other microorganisms, [38][39][40][41] particularly for metal-induced stress, for example, extracellular protein induction in ericoid fungi grown in the presence of zinc.…”

“…pannorum. [25] Superoxide dismutases are oxidative-stress response enzymes: Mn-SOD expression is increased in rat lung epithelial cells after asbestos-fiber inhalation [46] and in vitro treatment of human lymphocytes with SOD inhibited cell death due to previous crocidolite incubation. [47] In this respect, mammals and fungal cells seem to have developed a homologous reaction in the presence of asbestos fibers.…”

“…[24,25] Crocidolite, however, is not the most common type of asbestos, being confined mainly to relatively small deposits in South Africa, China, and Australia. The greatest percentage of the asbestos mined and manufactured is chrysotile, the most common fibrous serpentine.…”

FUNGAL LEACHING OF IRON ORE: ISOLATION, CHARACTERIZATION AND BIOLEACHING STUDIES OF <i>PENICILLIUM VERRUCULOSUM</i>

“…Microbes convert metal compounds into their water soluble forms and are biocatalysts of leaching processes. Many microbes have mechanisms that enable access to ion from poorly soluble forms (Martino et al, 2004). One possible way to obtain iron from low grade ores is through the microbial leaching.…”