Silver tolerance and accumulation in yeasts.
Debaryomyces hansenii (NCYC 459 and strain 75-21), Candida albicans (3153A), Saccharomyces cerevisiae (X2180-1B), Rhodotorula rubra (NCYC 797) and Aureobasidium pullulans (IMI 45533 and ATCC 42371) were grown on solid medium supplemented with varying concentrations of AgNO3. Although Ag+ is highly toxic towards yeasts, growth on solid media was still possible at Ag concentrations of 1-2 mM. Further subculture on higher Ag concentrations (up to 5 mM) resulted in elevated tolerance. The extent of Ag tolerance depended on whether Ag-containing plates were exposed to light prior to inoculation since light-mediated reduction of Ag+ to Ag0 resulted in the production of a less toxic silver species. Experimental organisms exhibited blackening of colonies and the surrounding agar during growth on AgNO3-containing medium especially at the highest Ag concentrations tested. All organisms accumulated Ag from the medium; electron microscopy revealed that silver was deposited as electron-dense granules in and around cell walls and in the external medium. X-ray microprobe analysis indicated that these granules were metallic Ag0 although AgCl was also present in some organisms. Volatile and non-volatile reducing compounds were produced by several test organisms which presumably effected Ag+ reduction to Ag0.
Kierans
M
M
Department of Biological Sciences, University of Dundee, UK.
Staines
A M
AM
Bennett
H
H
Gadd
G M
GM
D002176:Candida albicans / Q000187:drug effects; D004361:Drug Tolerance / Q000502:physiology; D004577:Electron Probe Microanalysis; D008854:Microscopy, Electron; D012248:Rhodotorula / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000187:drug effects; D012834:Silver / Q000378:metabolism / Q000633:toxicity*; D015003:Yeasts / Q000187:drug effects* / Q000378:metabolism
D012834:Silver