HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Holmes, J. D. Articles by Sodeau, J. R. Search for Related Content PubMed PubMed Citation Articles by Holmes, J. D. Articles by Sodeau, J. R. Agricola Articles by Holmes, J. D. Articles by Sodeau, J. R.

Cadmium-specific formation of metal sulfide ‘Q-particles’ by Klebsiella pneumoniae

School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK

¹ Author for correspondence: David J. Richardson. Tel: +44 1603 593250. Fax: +44 1603 592250. e-mail: d.richardson@uea.ac.uk

ABSTRACT

Summary: Klebsiella pneumoniae overcomes cadmium toxicity through the ‘biotransformation’ of cadmium ions into photoactive, nanometre-sized CdS particles deposited on the cell surface. The kinetics of particle formation during batch culture growth was monitored by electron microscopy (EM), energy-dispersive X-ray analysis and electronic absorption spectroscopy (EAS). During the deceleration phase of bacterial growth, the presence of CdS particles on the outer cell wall of K. pneumoniae ( 5 nm in diameter) was detected by EM. The size of these electron-dense particles continued to increase throughout the stationary phase of growth, with some of the particles reaching a diameter >200 nm. The formation of the extracellular CdS particles contributed to around 3-4% of the total cell biomass. EAS undertaken on these extracellular ‘bio-CdS’ particles suggested that the large ‘superparticles’ observed by EM, e.g. 200 nm, were aggregates of smaller particles termed ‘Q-particles’, ~ 4 nm in diameter. Metal sulfide particles were not formed in batch cultures of K. pneumoniae grown in the presence of lead, zinc, mercury, copper or silver ions. Growth in the presence of lead ions resulted in the formation of extracellular electron-dense particles containing lead but not sulfide or phosphate. Intracellular phosphorus-containing electron-opaque particles were formed during growth in the presence of copper and mercury. Intracellular electron-dense particles were formed in the presence of zinc ions but these did not contain phosphorus. From these results it was thought that metal sulfide formation in K. pneumoniae showed some cadmium-specificity. When cadmium and zinc ions were both added to the growth medium, metal sulfide particles were formed that were predominantly composed of cadmium, e.g. 48.6% cadmium and 0.04% zinc. Similarly, when cadmium and lead ions were both present during growth only CdS particles formed. In both cases analysis of the cells by EAS confirmed the presence of CdS only. These observations suggest that the mechanism of CdS formation is unlikely to occur simply through a cadmium-induced release of hydrogen sulfide by the cells into the external environment. If hydrogen sulfide production was the mechanism of sulfide formation then metal sulfide particles containing lead and zinc ions in addition to cadmium ions should have been produced.

This article has been cited by other articles:

				C. L. Wang, P. D. Maratukulam, A. M. Lum, D. S. Clark, and J. D. Keasling Metabolic Engineering of an Aerobic Sulfate Reduction Pathway and Its Application to Precipitation of Cadmium on the Cell Surface Appl. Envir. Microbiol., October 1, 2000; 66(10): 4497 - 4502. [Abstract] [Full Text]