Ecology of sulfate reducing bacteria in relation to the fate and stability of metal(loid)s in a mining-impacted freshwater sediment.

摘要

Redox transformations of metal(loid)s in soils and sediments are governed by microbial activity working in the context of ambient physicochemical conditions. Resulting valence state changes alter metal(loid) speciation, often influencing solubility and toxicity. Sulfate-reducing bacteria (SRB) carry out one such transformation, and under reducing conditions at circumneutral pH, microbially-produced sulfide can precipitate aqueous-phase metals as poorly-soluble metal sulfides. I investigated the possible effect of microbial sulfidogenesis on trace element distribution in freshwater sediments of Lake Coeur d'Alene, ID, an environment historically impacted by lead and silver mining. Previous observations showed that these sediments are highly reduced and support abundant cultivable SRB populations, leading me to hypothesize that SRB activity may help restrict contaminant mobility. The approach I used to test my hypothesis was to collect sediment cores over an annual cycle, and to estimate SRB abundance and activity in relation to physicochemical parameters known to influence or be indicative of metal(loid) speciation and phase association. Two study sites were located in the contaminated Coeur d'Alene River delta, a third in the nearby pristine St. Joe River delta. Culture-based most probable number estimates revealed 102--106 SRB gm-1 wet eight sediment. Investigation of enrichment cultures led to the discovery of novel, metal-tolerant SRB strains A10T, CY1T and CY2. Small-subunit ribosomal gene sequence phylogeny combined with strain-specific differences in physiology, cell wall chemistry, and DNA-DNA similarity values supported recognition of A10T [Desulfosporosinus idahoensis ] as a novel species within the genus Desulfosporosinus, and strains CY1T [Desulfovibrio ferrireducens] and CY2 as one novel species within the genus Desulfovibrio. Analysis of parameters indicative of microbial sulfidogenesis, including acid volatile sulfide (AVS), ex situ rates of 35SO 4 respiration, as well as non-culture based estimates of total SRB abundance lend support to the hypothesis that microbial sulfidogenesis occurs in the Lake Coeur d'Alene system, occurs preferentially in contaminated areas of the lake, but may be limited by availability of suitable substrates, including the terminal electron acceptor, SO42-. However, because iron is extraordinarily abundant in this system (10--15% by dry weight) the overall influence of microbial sulfidogenesis on trace element mobility may be limited.