Gel sequestration of heavy metals by Klebsiella oxytoca isolated from iron mat.

The enterobacterium Klebsiella oxytoca strain BAS-10 was isolated from sediments under an iron mat formed in a stream receiving leached waters from pyrite mine tailings. Under anaerobic laboratory conditions, BAS-10 fermented Fe(III)-citrate and Na-citrate giving CH(3)COOH and CO(2). In the presence of ferric citrate, BAS-10 secreted quantities of a thick gel containing glucose and/or mannose, if not other sugars. Sugar residues were observed in microbial aggregates using the sugar-specific concanavalin A lectin conjugated with fluorescein and imaged by a scanning confocal laser microscope. The gel bound Fe(III) which quickly precipitated. During fermentation, however, half the initial Fe(III) concentration was reduced to Fe(II) which did not bind to the gel and remained in solution. BAS-10 showed a high tolerance to heavy metals. Its growth was not inhibited by 1 mM Zn-, Pb- or Cd-acetate. These cations also co-precipitated with the iron gel, suggesting a possible application of this strain for abatement of toxic metals under anaerobic conditions.

Heavy metal coprecipitation with hydrozincite [Zn(5)(CO(3))(2)(OH)(6)] from mine waters caused by photosynthetic microorganisms.

An iron-poor stream of nearly neutral pH polluted by mine tailings has been investigated for a natural phenomenon responsible for the polishing of heavy metals in mine wastewaters. A white mineralized mat, which was determined to be hydrozincite [Zn(5)(CO(3))(2)(OH)(6)] by X-ray diffraction analysis, was observed in the stream sediments mainly in spring. The precipitate shows a total organic matter residue of 10% dry weight and contains high concentrations of Pb, Cd, Ni, Cu, and other metals. Scanning electron microscopy analysis suggests that hydrozincite is mainly of biological origin. Dormant photosynthetic microorganisms have been retrieved from 1-year-old dry hydrozincite. The autofluorescent microorganisms were imaged by a scanning confocal laser microscope. A photosynthetic filamentous bacterium, classified as Scytonema sp. strain ING-1, was found associated with microalga Chlorella sp. strain SA1. This microbial community is responsible for the natural polishing of heavy metals in the water stream by coprecipitation with hydrozincite.

Adhesion of acinetobacter venetianus to diesel fuel droplets studied with In situ electrochemical and molecular probes

The adhesion of a recently described species, Acinetobacter venetianus VE-C3 (F. Di Cello, M. Pepi, F. Baldi, and R. Fani, Res. Microbiol. 148:237-249, 1997), to diesel fuel (a mixture of C12 to C28 n-alkanes) and n-hexadecane was studied and compared to that of Acinetobacter sp. strain RAG-1, which is known to excrete the emulsifying lipopolysaccharide, emulsan. Oxygen consumption rates, biomass, cell hydrophobicity, electrophoretic mobility, and zeta potential were measured for the two strains. The dropping-mercury electrode (DME) was used as an in situ adhesion sensor. In seawater, RAG-1 was hydrophobic, with an electrophoretic mobility (&mgr;) of -0.38 x 10(-8) m2 V-1 s-1 and zeta potential (zeta) of -4.9 mV, while VE-C3 was hydrophilic, with &mgr; of -0.81 x 10(-8) m2 V-1 s-1 and zeta of -10.5 mV. The microbial adhesion to hydrocarbon (MATH) test showed that RAG-1 was always hydrophobic whereas the hydrophilic VE-C3 strain became hydrophobic only after exposure to n-alkanes. Adhesion of VE-C3 cells to diesel fuel was partly due to the production of capsular polysaccharides (CPS), which were stained with the lectin concanavalin A (ConA) conjugated to fluorescein isothiocyanate and observed in situ by confocal microscopy. The emulsan from RAG-1, which was negative to ConA, was stained with Nile Red fluorochrome instead. Confocal microscope observations at different times showed that VE-C3 underwent two types of adhesion: (i) cell-to-cell interactions, preceding the cell adhesion to the n-alkane, and (ii) incorporation of nanodroplets of n-alkane into the hydrophilic CPS to form a more hydrophobic polysaccharide-n-alkane matrix surrounding the cell wall. The incorporation of n-alkanes as nanodroplets into the CPS of VE-C3 cells might ensure the partitioning of the bulk apolar phase between the aqueous medium and the outer cell membrane and thus sustain a continuous growth rate over a prolonged period.