Deflocculation of Activated Sludge by the Dissimilatory Fe(III)-Reducing Bacterium Shewanella alga BrY.

The influence of microbial Fe(III) reduction on the deflocculation of autoclaved activated sludge was investigated. Fe(III) flocculated activated sludge better than Fe(II). Decreasing concentrations of Fe(III) caused an increase in sludge bulk water turbidity, while bulk water turbidity remained relatively constant over a range of Fe(II) concentrations. Cells of the dissimilatory metal-reducing bacterium Shewanella alga BrY coupled the oxidation of H(inf2) to the reduction of Fe(III) bound in sludge flocs. Cell adhesion to the Fe(III)-sludge flocs was a prerequisite for Fe(III) reduction. The reduction of Fe(III) in sludge flocs by strain BrY caused an increase in bulk water turbidity, suggesting that the sludge was deflocculated. The results of this study support previous research suggesting that microbial Fe(III) respiration may have an impact on the floc structure and colloidal chemistry of activated sludge.

Melanin production by a filamentous soil fungus in response to copper and localization of copper sulfide by sulfide-silver staining.

Gaeumannomyces graminis var. graminis, a filamentous soil ascomycete, exhibited enhanced cell wall melanin accumulation when exposed to as little as 0.01 mM CuSO(inf4) in minimal broth culture. Because its synthesis was inhibited by tricyclazole, the melanin produced in response to copper was dihydroxynaphthalene melanin. An additional hyphal cell wall layer was visualized by electron microscopy when hyphae were grown in the presence of copper and fixed by cryotechniques. This electron-dense layer was between the outer cell wall and the inner chitin layer and doubled the total wall thickness. In copper-grown cells that were also treated with tricyclazole, this electron-dense layer was absent. Atomic absorption spectroscopy demonstrated that up to 3.5 mg of Cu per g of fungal mycelium was adsorbed or taken up by hyphae grown in 0.06 mM CuSO(inf4). A method for silver enhancement was developed to determine the cellular location of CuS. CuS was present in cell walls and septa of copper-grown hyphae. Electron microscopy of silver-stained cells suggested that CuS was associated with the melanin layer of cell walls.