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Considerable progress has been made towards enhancing our understanding of the phylogeny, ecology and biogeochemical role of dissimilatory iron-reducing bacteria. The known phylogenetic range of iron-reducing bacteria has expanded considerably, as has the known range of iron minerals that serve as a source of Fe(III) for anaerobic respiration. In addition, the number of biotechnological applications of iron-reducing bacteria, including remediation of soils and sediments contaminated with metals, radionuclides and organics, is rapidly expanding.

Intact magnetosomes of Aquaspirillum magnetotacticum were purified from broken cells by a magnetic separation technique. Electron microscopic and chemical analyses revealed the magnetite to be enclosed by a lipid bilayer admixed with proteins. Lipids were recovered in fractions expected to contain (i) neutral lipids and free fatty acids, (ii) glycolipids and sulfolipids, and (iii) phospholipids (in a weight ratio of 1:4:6). Phospholipids included phosphatidylserine and phosphatidylethanolamine. Two of the numerous proteins detected in the magnetosome membrane were not found in other cell membranes or soluble fractions.

Presents a study which investigated the magnetic properties of intracellular magnetite crystals in the bacterium, Aquaspirillum magnetotacticum. Experimental details; Results and discussion; Conclusions.

This investigation documents the formation of Green Rust (GR) and immobilization of Ni[sup 2+] in response to bacterial reduction of hydrous ferric oxide (HFO). In the absence of Ni[sup 2+], 79% of the total Fe(III) present as HFO was reduced; at 10[sup -3] and 10[sup -4] M Ni[sup 2+], 36% of the total Fe(III) was reduced, whereas 45 to 50% of the total Fe(III) was reduced at 10[sup -5] M Ni[sup 2+]. The inhibitory effect of 10[sup -3] and 10[sup -4] M Ni[sup 2+] on Fe(III)-reduction corresponded to a 50% decrease in number of viable cells relative to the Ni[sup 2+]-free condition, and a 25% decrease at 10[sup -5] M Ni[sup 2+]. A prominent GR peak at d = 10.9 nm was evident in X-ray diffraction patterns of postreduction residual solids from the cultures. Minor peaks arising for vivianite and magnetite were also present. In samples prepared for scanning electron microscopy, thin hexagonal plates of GR were easily distinguished as a solid phase transformation product of HFO. Small hexagonal sheets and fragments of larger GR plates were also observed in transmission electron microscopy whole mounts together with bacteria that were mineralized by surface precipitates of microcrystalline magnetite. Energy dispersive spectroscopy (EDS) confirmed that GR contained Fe and P, as well as Ni in those samples taken from the Ni[sup 2+]-amended experiments. EDS detected neither P nor Ni in the magnetite precipitates associated with the bacterial cells. Dissolved Ni2 + concentrations decreased in an exponential fashion with respect to time in all experimental systems, corresponding to an overall first-order rate constant k of -0.030 day[sup -1]. At the same time, a strong linear relationship (r[sup 2] = 0.99) between the dissolved and solid phase Ni[sup 2+]/Fe[sup 2+] ratios over the entire period of the Fe(III)reduction experiments provided evidence that the solid-phase partitioning of Ni[sup 2+] in GR extended from equilibrium solid-solution behavior. [ABSTRACT FROM AUTHOR]