Recognition of Error Symptoms in Large Systems

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryJoint Services Electronics Program / N00014-84-C-0149IBM Corporatio

Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors

MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV–vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately -500 mV (vs. the standard hydrogen electrode). Across this potential window the UV–vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled low-spin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate

Oxidation of arsenite by Agrobacterium albertimagni, AOL15, sp. nov., isolated from Hot Creek, California

An arsenite-oxidizing bacterium, Agrobacterium albertimagni strain AOL15 (ATCC BAA-24), was isolated from the surface of aquatic macrophytes collected in Hot Creek, California. Under laboratory conditions, whole cell suspensions of AOL15 oxidized arsenite with a Ks of 3.4 ± 2.2 μM and a Vmax of 1.81 ± 0.58 × 10-12 μmole · cell-1 · min-1 (or 0.043 ± 0.017 μmole · mg protein-1 · min-1). The Ks value for AOL15 is the lowest value to date reported for whole cell suspensions and is comparable to ambient concentrations of arsenic of 2.7 μM reported for Hot Creek, indicating that AOL15 can oxidize arsenite under ambient conditions. Previous studies at this site revealed a rapid in situ oxidation of geothermally-derived arsenite while field incubation studies demonstrated that this oxidation was bacterially mediated. The isolation of the arsenite oxidizer AOL15 from this environment supports these previous observations. Arsenite does not support chemolithoautotrophic growth of AOL15 and toxicity studies with AOL15 showed that arsenite (at 5 mM) is toxic to AOL15, yet arsenate concentrations as high as 50 mM do not show any toxic effects. These results suggest that the oxidation of arsenite by AOL15 is a detoxification mechanism

DddY, a periplasmic dimethylsulfoniopropionate lyase found in taxonomically diverse species of Proteobacteria

The abundant compatible solute dimethylsulfoniopropionate (DMSP) is made by many marine algae. Different marine bacteria catabolise DMSP by various mechanisms, some of which liberate the environmentally important gas dimethyl sulfide (DMS). We describe an enzyme, DddY, which cleaves DMSP into DMS plus acrylate and is located in the bacterial periplasm, unlike other DMSP lyases that catalyse this reaction. There are dddY-like genes in strains of Alcaligenes, Arcobacter and Shewanella, in the β-, ɛ- and γ-proteobacteria, respectively. In Alcaligenes, dddY is in a cluster of ddd and acu genes that resemble, but also have significant differences to, those in other bacteria that catabolise both DMSP and acrylate. Although production of DMS and transcription of Alcaligenes dddY are both apparently inducible by pre-growth of cells with DMSP, this substrate must be catabolised to form acrylate, the bona fide coinducer