Gel sequestration of heavy metals by Klebsiella oxytoca isolated from ironmat

The enterobacterium Klebsiella oxytoca strain BAS-10 was isolated from sedi ments under an iron mat Termed in a stream receiving leached waters from py rite mine tailings. Under anaerobic laboratory conditions, BAS-10 fermented Fe(III)-citrate and Na-citrate giving CH3COOH and CO2. In the presence of ferric citrate, BAS-10 secreted quantities of a thick gel containing glucos e and/or mannose, if not other sugars. Sugar residues were observed in micr obial aggregates using the sugar-specific concanavalin A lectin conjugated with fluorescein and imaged by a scanning confocal laser microscope. The ge l bound Fe(III) which quickly precipitated. During fermentation, however, h alf the initial Fe(III) concentration was reduced to Fr(II) which did not b ind to the gel and remained in solution. BAS-10 showed a high tolerance to heavy metals. Its growth was nor 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 c onditions. (C) 2001 Federation of European Microbiological Societies, Publi shed by Elsevier Science B.V. All rights reserved.