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D Ahmann

Publications and source records attributed to D Ahmann.

4 recordsLinked to original sources
PubMed1997

Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov.

A newly discovered arsenate-reducing bacterium, strain OREX-4, differed significantly from strains MIT-13 and SES-3, the previously described arsenate-reducing isolates, which grew on nitrate but not on sulfate. In contrast, strain OREX-4 did not respire nitrate but grew on lactate, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly used by sulfate reducers. Scorodite (FeAsO42. H2O) an arsenate-containing mineral, provided micromolar concentrations of arsenate that supported cell growth. Physiologically and phylogenetically, strain OREX-4 was far-removed from strains MIT-13 and SES-3: strain OREX-4 grew on different electron donors and electron acceptors, and fell within the gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell together in the epsilon-subdivision of the Proteobacteria. Together, these results suggest that organisms spread among diverse bacterial phyla can use arsenate as a terminal electron acceptor, and that dissimilatory arsenate reduction might occur in the sulfidogenic zone at arsenate concentrations of environmental interest. 16S rRNA sequence analysis indicated that strain OREX-4 is a new species of the genus Desulfotomaculum, and accordingly, the name Desulfotomaculum auripigmentum is proposed.

Arsenates↗
PubMed1991

Rhizobium meliloti exopolysaccharides: genetic analyses and symbiotic importance.

Genetic experiments have indicated that succinoglycan (EPS I), the acidic Calcofluor-binding exopolysaccharide, of the nitrogen-fixing bacterium Rhizobium meliloti strain Rm1021 is required for nodule invasion and possibly for later events in nodule development on alfalfa and other hosts. Fourteen exo loci on the second megaplasmid have been identified that are required for, or affect, the synthesis of EPS I. Mutations in certain of these loci completely abolish the production of EPS I and result in mutants that form empty Fix- nodules. We have identified two loci, exoR and exoS, that are involved in the regulation of EPS I synthesis in the free-living state. Certain exo mutations which completely abolish EPS I production are lethal in an exoR95 or exoS96 background. Histochemical analyses of the expression of exo genes during nodulation using exo::TnphoA fusions have indicated that the exo genes are expressed most strongly in the invasion zone. In addition, we have discovered that R. meliloti has a latent capacity to synthesize a second exopolysaccharide (EPS II) that can substitute for the role(s) of EPS I in nodulation of alfalfa but not of other hosts. Possible roles for exopolysaccharides in symbiosis are discussed.

Genes, Bacterial↗
PubMed1975

Biological markers in breast carcinoma. I. Incidence of abnormalities of CEA, HCG, three polyamines, and three minor nucleosides.

Patients with breast carcinoma were screened for abnormal concentrations of CEA, HCG, putrescine, spermidine, spermine, pseudouridine, N2, N2-dimethylguanosine, and 1-methylinosine. Abnormal polyamine levels occurred in less than 15% of the patients. Among the nucleosides, N2, N2-dimethylguanosine was the most frequently abnormal, occurring in 57% of the patients with metastatic disease. CEA levels were abnormal in 30% of postoperative N+ patients and 74% of patients with metastatic disease, while HCG elevations were found in 45% and 50%, respectively. All the patients with one or more marker abnormalities could be detected by measuring only CEA, N2, N2-dimethylguanosine, and HCG. Among these three tests, a singular marker abnormality occurred in 35.8% of the patients, and all three tests were abnormal in 21.8% of the patients. The performance of these three tests in each patient revealed one or more abnormalities 97% of the patients with metastatic disease, and 67% of the postoperative N+ patients.

Breast Neoplasms↗