Glutamic acid leaching of synthetic covellite - A model system combining experimental data and geochemical modeling.

For Kupferschiefer mining established pyrometallurgical and acidic bioleaching methods face numerous problems. This is due to the finely grained and dispersed distribution of the copper minerals, the complex mineralogy, comparably low copper content, and the possibly high carbonate and organic content in this ore. Leaching at neutral pH seemed worth a try: At neutral pH the abundant carbonates do not need to be dissolved and therewith would not consume excessive amounts of provided acids. Certainly, copper solubility at neutral pH is reduced compared to an acidic environment; however, if copper complexing ligands would be supplied abundantly, copper contents in the mobile phase could easily reach the required economic level. We set up a model system to study the effect of parameters such as pH, microorganisms, microbial metabolites, and organic ligands on covellite leaching to get a better understanding of the processes in copper leaching at pH ≥ 6. With this model system we could show that glutamic acid and the microbial siderophore desferrioxamine B promote covellite dissolution. Both experimental and modeling data showed that pH is an important parameter in covellite dissolution. An increase of pH from 6 to 9 could elevate copper extraction in the presence of glutamic acid by a factor of five. These results have implications for both development of a biotechnological process regarding metal extraction from Kupferschiefer, and for the interaction of bacterial metabolites with the lithosphere and potential mobilization of heavy metals in alkaline environments.

Compliance of the digital artery is decreased in patients with essential hypertension.

The compliance of the arterial vascular system is decreased in hypertensive subjects. On the other hand, the vessel wall properties such as compliance depend on blood pressure (BP). The aim of the present study was to determine the compliance of the digital arteries and to test the hypothesis that decreased compliance is either caused by a downward shift of the compliance-pressure relation or, alternatively, by a change in the compliance-pressure relation itself. We used impedance plethysmography and a finger BP measuring device to determine beat-to-beat the pressure-pulse amplitude (delta P), the volume-pulse amplitude (delta V) and the compliance from digital arteries of 10 hypertensive patients and 10 similarly aged normal subjects. The mean local blood pressure (MLBP) in the digital arteries was changed by vertically varying the position of the right hand in relation to the heart. The compliance of the digital arteries in hypertensive patients (2.76 microliters/mm Hg per 100 ml tissue) is significantly (P < 0.05) decreased compared with that in normal subjects (4.03 microliters/mm Hg per 100 ml tissue). A reduction of MLBP by 50 mm Hg leads to an increase of compliance in normotensive subjects from 4.03 to 12.68 microliters/mm Hg per 100 ml tissue but in hypertensive patients only from 2.76 to 6.16 microliters/mm Hg per 100 ml tissue. The slope of the curve in the low pressure range was also markedly decreased in hypertensive patients compared with controls. We conclude, that the compliance-pressure relation is not merely shifted but also extensively alterated in hypertensive patients.

Mutagenesis of acetobacter methanolicus MB58 with the transposon Tn5.

Transposon mutagenesis was applied to the isolation of mutants of the facultatively methylotrophic Acetobacter methanolicus MB 58. The transposon Tn5 (pSU2011) was transferred from Escherichia coli SM 10 by means of conjugation to Acetobacter methanolicus MB 58. Four out of 1850 stable Km-resistant transconjugants were identified that were formaldehyde sensitive and failed to grow on methanol.

Detoxification of formaldehyde by acetic acid bacteria.

Formaldehyde resistance of methylotrophic and non-methylotrophic Acetobacter strains was investigated. A facultatively methylotrophic Acetobacter methanolicus (MB58) gets rid of free formaldehyde by assimilating it. Heterotrophically growing cells tolerate 12 mM free formaldehyde. Non-methylotrophic but methanol oxidizing Acetobacter pasteurianus strains possess the same level of formaldehyde resistance. Formaldehyde resistance can be drastically lowered down to 4 mM by blocking the formate dehydrogenase by means of hypophosphite. Acetobacter spp. Martin 1 and LMG 76.10 are not able to oxidize methanol or formaldehyde via formate to CO2 and possess a significantly lower formaldehyde resistance (4 mM). Hence high formaldehyde resistance of the Acetobacter spp. investigated is based above all on a properly operating linear dissimilatory sequence. The dissimilatory RuMP cycle can hardly help detoxify formaldehyde.