Year: 2000
Type: article
Abstract: This study was designed to determine whether chemolithotrophic bacteria that derive " metabolic energy from iron oxidation can be sustained by the flux of ferrous iron released by dissolution of fayalite (Fe2Si04) and to evaluate the impact of metabolic products on the dissolution kinetics.When fayalite was dissolvqd abiotically, almost all dissolved iron remained as Fe2+over the duration of the experiment.However, in the presence of l%iobacihsferrooxidans aqueous iron was oxidized to Fe3+.Dead cells did not induce si-gificant ferrous iron oxidation and had minimal effect on the reaction rate.These results confirm that T.ferrooxidans was active in our experiments and can be sustained by fayalite dissolution.In the presence of Z ferrooxidam the total Fe accumulated in solution was only 5 to 50% of that in abiotic experiments.Silicon was not strongly incorporated into secondary minerals.Thus, Si release rates can be used to evaluate fayalite dissolution rates.The data indicate inhibition of fayalite dissolution in the presence of microorganisms.TEM and SEM analyses confirm that fayalite in the biotic experiments was much less extensively reacted than in the organism-free experiments.However, some precipitation of secondary iron oxyhydroxide minerals, especially in .proximity to cells, leads to solutions with different stoichiometry than that of fayalite.The iron oxyhydroxides occur as aggregates of few nanometer diameter particles.These are unlikely to suppress the reaction rate via diffusion inhibition.Consequently, abiotic experiments were conducted to test the hypothesis that the ferric iron byproduct of $ microbial metabolism was responsible for the decreased dissolution rates in biological experiments..4ddition of aqueous Fe3+inhibited both silica and iron release byapproximately 30°/0compared to the abiotic control, but added Fe*+and Mg2+had no ' effect.The similarity between the extent of inhibition due to addition of very low concentrations of Fe3+and the rate suppression observed in biological experiments suggests that Fe3+adsorption to surfaces sites is the primary cause for lower rate of accumulation of iron in solution in biological experiments.We propose biological inhibition of fayalite dissolution is due to binding of ferric iron to ferrous iron sites on the \ fayalite stiace.This may generate a laihunite-like (-Fe+O.gFe+o.gSi04)stiace layer that is fundamentally iess reactive than fayalite.-----..-m.
Language: English
Subfield: Metals and Alloys
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1932089392