Toxicity of Al to Desulfovibrio desulfuricans

Abstract

The toxicity of Al to Desulfovibrio desulfuricans G20 was assessed over a period of 8 weeks in a modified lactate C medium buffered at four initial pHs (5.0, 6.5, 7.2, and 8.3) and treated with five levels of added Al (0, 0.01, 0.1, 1.0, and 10 mM). At pH 5, cell population densities decreased significantly and any effect of Al was negligible compared to that of the pH. At pHs 6.5 and 7.2, the cell population densities increased by 30-fold during the first few days and then remained stable for soluble-Al concentrations of <5 ؋ 10 ؊5 M. In treatments having total-Al concentrations of >1 mM, soluble-Al concentrations exceeded 5 ؋ 10 ؊5 M and limited cell population growth substantially and proportionally. At pH 8.3, soluble-Al concentrations were below the 5 ؋ 10 ؊5 M toxicity threshold and cell population density increases of 20-to 40-fold were observed. An apparent cell population response to added Al at pH 8.3 was attributed to the presence of large, spirilloidal bacteria (accounting for as much as 80% of the cells at the 10 mM added Al level). Calculations of soluble-Al speciation for the pH 6.5 and 7.2 treatments that showed Al toxicity suggested the possible presence of the Al 13 O 4 (OH) 24 (H 2 O) 12 7؉ "tridecamer" cation and an inverse correlation of the tridecamer concentration and the cell population density. Analysis by 27 Al nuclear magnetic resonance spectroscopy, however, yielded no evidence of this species in freshly prepared samples or those taken 800 days after inoculation. Exclusion of the tridecamer species from the aqueous speciation calculations at pHs 6.5 and 7.2 yielded inverse correlations of the neutral Al(OH) 3 and anionic Al(OH) 4 ؊ monomeric species with cell population density, suggesting that one or both of these ions bear primary responsibility for the toxicity observed.Aluminum, the most abundant metal and the third most abundant element in the earth's crust (37), finds surprisingly little use in biological systems. Although the inherent chemistry of Al certainly is a factor, the chemical conditions existing on the earth at the time the earliest organisms were developing may also have played a role (42, 43). These conditions, which include neutral pH and the absence of oxygen, were such that the solubility of Al was minimal relative to that of divalent metals such as Mg, Ca, and Fe(II). Even if availability were not limiting, however, several other chemical properties of Al strongly militate against its use in cellular metabolism (5). The inherently slow rate of inner-sphere ligand exchange for Al 3ϩ (10 5 to 10 8 times slower than for Mg 2ϩ , Ca 2ϩ , or Fe 2ϩ [41]) makes its complexes relatively inert. Further inertness stems from the lack of any electron transfer chemistry. Moreover, Al 3ϩ forms complexes with greater thermodynamic stability than that of those formed by the divalent metals because of its smaller size and higher valence. Thus, the ability of Al to form strong, relatively inert complexes not only prevents its use by the cyclic feedback-regulated processes in cellu...

Aluminum and sulphate removal by a highly Al-resistant dissimilatory sulphate-reducing bacteria community

“…TEM-EDS analysis showed that the precipitates resulting from the biological activity were only formed outside the bacterial cells and were mainly composed by aluminum. In addition, XRD analysis showed that the precipitates were composed by amorphous aggregates, which is consistent with the formation of aluminium hydroxide reported as amorphous (Amonette et al 2003;Berkowitz et al 2005;Mikutta et al 2011). Therefore, the precipitation of aluminum as hydroxide after the lactate consumption could be the mechanism involved in Al removal by DSRB community.…”

“…at the neutral pH values, usually favourable for DSRB growth and activity ), lactate was used in the present study not only as a carbon source but also as an organic ligand that allows maintaining this metal soluble in the nutrient medium. In fact, aluminum lactate (AlLac 3 ) is largely used in toxicology experimentation because it is very soluble in water (Zatta et al 1998;Amonette et al 2003) and the solubility is even maintained at neutral pH (Amonette et al 2003).…”

Role of Lipid Composition and Lipid Peroxidation in the Sensitivity of Fungal Plant Pathogens to Aluminum Chloride and Sodium Metabisulfite

“…Theses results are in agreement with other studies that have postulated that, under certain conditions, aluminum chloride and sodium metabisulfite may act through cell disruption, compromised membrane permeability, and lipid peroxidation (1,3,6,15,17,34).…”

“…For example, fungi that are more tolerant to the antimicrobial effects of these salts may have greater antioxidant activities that would reduce or nullify the effect of peroxidation by breaking the propagation cycle (8). Furthermore, it is not improbable that other modes of action of aluminum chloride and sodium metabisulfite exist, as other antimicrobial activities of these salts (reactions with protein disulfide groups [4,15,26] and inhibition of enzyme activity through the inactivation of cofactors [30] and coenzymes [23,26,27,28], in the case of sulfites, and replacement of divalent metal complexes [1] and complexation with ATP [11], DNA [31], and phosphates [24], for aluminum) have been reported and cannot be fully explained by lipid peroxidation. This study is the first, to our knowledge, to propose lipid peroxidation as a component of the inhibitory effects of aluminum chloride and sodium metabisulfite on fungal potato pathogens.…”

Ultrastructural Alterations of Erwinia carotovora subsp. atroseptica Caused by Treatment with Aluminum Chloride and Sodium Metabisulfite

“…Aluminum and bisulfite salts are toxic to several microorganisms including fungi (7,15,16) and bacteria (1,8). Aluminum chloride and sodium metabisulfite were shown to be toxic at low concentrations against Erwinia carotovora subsp.…”