Energy-dispersive X-ray analysis of the extracellular cadmium sulfide crystallites of Klebsiella aerogenes

Abstract

Klebsiella aerogenes forms electron-dense particles on the cell surface in response to the presence of cadmium ions in the growth medium. These particles ranged from 20 to 200 nm in size, and quantitative energy dispersive X-ray analysis established that they comprise cadmium and sulfur in a 1:1 ratio. This observation leads to the conclusion that the particles are cadmium sulfide crystallites. A combination of atomic absorption spectroscopy, inductively coupled plasma mass spectrometry, and acid-labile sulfide analysis revealed that the total intracellular and bound extracellular cadmium:sulfur ratio is also 1:1, which suggests tha the bulk of the cadmium is fixed as extracellular cadmium sulfide. The tolerance of K. aerogenes to cadmium ions and the formation of the cadmium sulfide crystallites were dependent on the buffer composition of the growth medium. The addition of cadmium ions to phosphate-buffered media resulted in cadmium phosphate precipitates that remove the potentially toxic cadmium ions from the growth medium. Electron-dense particles formed on the surfaces of bacteria grown under these conditions were a combination of cadmium sulfide and cadmium phosphates. The specific bacterial growth rate in the exponential phase of batch cultures was not affected by up to 2mM cadmium in Tricine-buffered medium, but formation of cadmium sulfide crystallites was maximal during the stationary phase of batch culture. Cadmium tolerance was much lower (10 to 150 microM) in growth media buffered with Tris, Bistris propane, Bes, Tes, or Hepes. These results illustrate the importance of considering medium composition when comparing levels of bacterial cadmium tolerance.

Identification of SLF1 as a New Copper Homeostasis Gene Involved in Copper Sulfide Mineralization in Saccharomyces cerevisiae

“…The first potential translation initiation ATG triplet is a perfect match with the Kozak consensus in yeast cells, with the sequence (A/C)A(A/C)AAT GTC(C/T) (18). Northern analysis revealed an mRNA of nearly 1,500 nucleotides, consistent with a protein of 447 residues.…”

“…Deposition of Cd(II) ions into cadmium sulfide mineral particles occurs in certain strains of bacteria. X-ray analysis of extracellular cadmium sulfide crystallites in Klebsiella aerogenes revealed particles ranging in size from 20 to 200 nm, and the crystallites contained cadmium and sulfur in a 1:1 ratio (18).…”

Survival Strategies of the Plant-Associated Bacterium Enterobacter sp. Strain EG16 under Cadmium Stress

“…The cells were then fixed in 4% glutaraldehyde, washed three times in phosphate buffer, fixed in 1% osmium tetroxide, washed again in phosphate buffer, dehydrated though a graded series of ethanol solutions (30%, 50%, 70%, 90%, and 100%), soaked in propylene oxide, and finally embedded in Epon 812 epoxy resin for ultrathin sections (Leica, Austria) and subjected to transmission electron microscopy (TEM) analysis (JEOL, Japan). Electron-dense granules found via TEM were further examined by energy-dispersive X-ray (EDX) analysis as performed by Holmes et al (2). Each treatment was prepared with three replicates.…”

“…Metal extraction activities are major sources for heavy metals in the environment (1). Cadmium is highly toxic to plants, animals, microorganisms, and humans even at quite low concentrations (2,3). Although Cd is non-redox active, it can cause oxidative stress by generating reactive oxygen species (ROS) (4), which can lead to DNA damage (5), inhibit the DNA mismatch repair system (6), and disrupt the synthesis of nucleic acids and proteins (7).…”

Biosynthesis and stabilization of Au and Au–Ag alloy nanoparticles by fungus,Fusarium semitectum

“…Microorganisms, including viruses, bacteria, and fungi [3,4], grow into unique and structurally interesting forms that have been used by many researchers as templates for the self-organization of inorganic materials with the aim of realizing functional macrostructures. In such assemblies, the inherent uniformity of the biological structures can be combined with the functional properties of inorganic nanoparticles [5][6][7] (such as conductivity and optical activity) to realize functional macrostructures. As an example, a dense assembly of nanoparticles on filamentous fungi [8] with typical hyphal diameters of a few micrometers (varying from species to species) and lengths varying from tens of micrometers to a few millimeters could find immediate applications as circuit components.…”