The magnetococcus, a magnetotactic bacterium, has been grown in a complex simulated natural environment. Sufficiently pure samples of cells were obtained magnetically making axenic cultures unnecessary for many purposes. The magnetococcus is a Gram-negative coccus, 1.6 micron in diameter and readily distinguished by highly refractile inclusions and its magnetotactic behavior. This organism is actively motile by means of two bundles of flagella. Electron dense ferromagnetic inclusions were localized between the flagellar bundles. Collections of magnetococci were morphologically homogeneous and negligibly contaminated by extraneous bacteria. DNA extracted from pooled collections of cells was homogeneous by analytical CsC1 centrifugation. The guanine-cytosine content was 61.7%. Total iron by percent cellular dry weight was 3.8%. Comparisons with a previously described magnetotactic marine coccus were made.

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Methanosarcina barkeri was adapted to grow on carbon monoxide by sequential transfer of the culture in medium that contained CO (100% of culture headspace). These experiments document the ability of the organism to grow slowly (65-h doubling time) and to produce methane and CO2 either on CO as the sole carbon and energy source or by the simultaneous consumption of methanol and CO. During growth on CO as carbon and energy source, net hydrogen formation occurred when the CO partial pressure in the culture headspace was greater than 20% CO, but hydrogen was consumed when the CO concentration was below this value.Carbon monoxide is an abundant atmospheric pollutant generated by incomplete conbustion of fossil fuels. Carbon monoxide is also formed as a metabolite of microbial metabolism, especially heme degradation by aerobic microorganisms (5,19). The physiological features of anaerobic bacteria that are able to grow on various one-carbon substrates as the sole carbon and electron source (i.e., unicarbonotrophic growth) and to grow mixotrophically on mixtures of onecarbon substrates, including CO, have been reviewed (20). Several genera of anaerobic bacteria have been shown to grow on CO as the energy source, including: Rhodopseudomonas (18), Methanobacterium (2), Butyribacterium (4), Eubacterium (13), Clostridium (9), and Acetobacterium (8).Kluyver and Schnellen (10) demonstrated that Methanosarcina barkeri produced 1 mol of methane and 3 mol of CO2 from 4 mol of CO when cell suspensions were incubated under 1 atm (ca. 101.29 kPa) (100%) of this gas. Later, Daniels et al.(2) showed that M. barkeri oxidized small amounts of added CO during growth on H2-CO2 and that cell extracts contained a methyl viologen-linked CO dehydrogenase activity. The significance of CO metabolism by some anaerobes like Clostridium pasteurianum is enigmatic because this anaerobe consumes CO via CO dehydrogenase activity, but it is not capable of growth on this substrate (3). However, it was established that acetogenic species, like Clostridium thermoaceticum, made acetate during growth with CO as the carbon and energy source (9). Carbon monoxide dehydrogenase has been proposed to function in carbonylation of a methyl group during acetyl-coenzyme Aacetate synthesis in both acetogenic (6) and methanogenic (7, 17) anaerobes. Krzycki and Zeikus (11) reported that the level of this enzyme increased fivefold when M. barkeri was grown on acetate versus on H2-CO2 or methanol as the sole carbon and energy source. This result suggested that CO dehydrogenase of M. barkeri may also function in acetate dissimilation by a biochemical mechanism that involves the production and consumption of a carbonyl group as an intermediary step in methane and CO2 formation. In the present note, we show that M. barkeri is able to grow either * Corresponding author. unicarbonotrophically with CO as the sole carbon and energy source or mixotrophically with CO and methanol.M. barkeri neotype strain MS was routinely cultivated under strictly anoxic conditions in a phosphat...

The morphological, biochemical, and magnetotactic properties of a single magnetic bacterium are reported. Although this bacterium has not been cultured axenically, the unusual magnetotactic behavior has allowed the collection of cell material of sufficient quantity and purity to allow characterization. The results indicate that this organism represents a new genus of colorless, sulfur-depositing bacteria, albeit of uncertain affiliation. The name proposed for this new genus/species, Bilophococcus magnetotacticus, reflects the most distinctive traits of morphology, motility, and magnetic mineral formation. Classification is based on type descriptive material.

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A chemotaxis system for Pseudomonas aeruginosa was defined by using the method of Adler. Cells were attracted to compounds in the order ammonium chloride > amino acids > organic acids. Two sugars were assayed and elicited no response. Comparisons with other model systems are discussed.

Magnetite particles isolated from magnetococcoid bacterial cells have been studied by high resolution transmission electron microscopy (h.r.t.e.m.). The particles show lattice images consistent with the magnetite structure and have a hexagonal prism habit truncated by {011} and {100} planes. The particles have a high degree of crystal perfection and are single domain structures. Some crystals showed a superimposed ‘graininess’ and ill-defined edges. In some crystals regular growth points on the crystal edge could be observed while in other crystals the material at the crystal edge appeared to be amorphous. These results suggest that the crystals are often surrounded by an amorphous phase. These observations are consistent with a model of crystal formation which involves nucleation of the magnetite phase at one primary site followed by slow crystal growth. It is proposed that crystal growth proceeds by dissolution of kinetically favoured precursor iron oxide phases aggregated or precipitated at the magnetite surface of the primary crystal followed by incorporation of soluble ferric-ferrous hydroxo-complexes into the magnetite lattice. The possible roles of the surrounding membrane in magnetite synthesis are discussed.