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D A Bazylinski

Publications and source records attributed to D A Bazylinski.

At least 19 recordsLinked to original sources
PubMed2004

Spatiotemporal distribution of marine magnetotactic bacteria in a seasonally stratified coastal salt pond.

The occurrence and distribution of magnetotactic bacteria (MB) were studied as a function of the physical and chemical conditions in meromictic Salt Pond, Falmouth, Mass., throughout summer 2002. Three dominant MB morphotypes were observed to occur within the chemocline. Small microaerophilic magnetite-producing cocci were present at the top of the chemocline, while a greigite-producing packet-forming bacterium occurred at the base of the chemocline. The distributions of these groups displayed sharp changes in abundance over small length scales within the water column as well as strong seasonal fluctuations in population abundance. We identified a novel, greigite-producing rod in the sulfidic hypolimnion that was present in relatively constant abundance over the course of the season. This rod is the first MB that appears to belong to the gamma-Proteobacteria, which may suggest an iron- rather than sulfur-based respiratory metabolism. Its distribution and phylogenetic identity suggest that an alternative model for the ecological and physiological role of magnetotaxis is needed for greigite-producing MB.

DNA, Bacterial↗
PubMed2001

Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures.

McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.

Bacterial Physiological Phenomena↗
PubMed2000

Elongated prismatic magnetite crystals in ALH84001 carbonate globules: potential Martian magnetofossils.

Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment. In this study, we describe six properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria), properties that, collectively, are not observed in any known population of inorganic magnetites. These criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories. Of the ALH84001 magnetites that we have examined, the elongated prismatic magnetite particles (similar to 27% of the total) are indistinguishable from the MV-1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals.

Biomarkers↗
PubMed2000

N2-dependent growth and nitrogenase activity in the metal-metabolizing bacteria, Geobacter and Magnetospirillum species.

Cells of Geobacter metallireducens, Magnetospirillum strain AMB-1, Magnetospirillum magnetotacticum and Magnetospirillum gryphiswaldense showed N2-dependent growth, the first anaerobically with Fe(III) as the electron acceptor, and the latter three species microaerobically in semi-solid oxygen gradient cultures. Cells of the Magnetospirillum species grown with N2 under microaerobic conditions were magnetotactic and therefore produced magnetosomes. Cells of Geobacter metallireducens reduced acetylene to ethylene (11.5+/-5.9 nmol C2H4 produced min(-1) mg(-1) cell protein) while growing with Fe(III) as the electron acceptor in anaerobic growth medium lacking a fixed nitrogen source. Cells of the Magnetospirillum species, grown in a semi-solid oxygen gradient medium, also reduced acetylene at comparable rates. Uncut chromosomal and fragments from endonuclease-digested chromosomal DNA from these species, as well as Geobacter sulphurreducens organisms, hybridized with a nifHDK probe from Rhodospirillum rubrum, indicating the presence of these nitrogenase structural genes in these organisms. The evidence presented here shows that members of the metal-metabolizing genera, Geobacter and Magnetospirillum, fix atmospheric dinitrogen.

Acetylene↗
PubMed1999

Genome analysis of several marine, magnetotactic bacterial strains by pulsed-field gel electrophoresis.

The genomic DNA of three strains of marine magnetotactic bacteria, including two facultatively anaerobic vibrios, strains MV-1 and MV-2, and the microaerophilic coccus, strain MC-1, was analyzed by pulsed-field gel electrophoresis (PFGE). Digestion of the genomic DNA of strain MV-1 by the restriction endonucleases AvrII, BamHI, HindIII, NheI, SalI, SfiI, SgfI, SgrAI, and XbaI resulted in a large number of fragments below 400 kb that were difficult to resolve by PFGE. Digestion of MV-1 DNA with NotI and RsrII resulted in no fragments. Treatment of genomic DNA of strains MV-1 and MV-2 with PacI, PmeI, and SpeI yielded a manageable number of fragments (ca. 20) that were relatively easily resolved with PFGE, while PacI and SpeI were effective for strain MC-1. There was no evidence for the presence of plasmids and linear chromosomes in any of the strains, and strains MV-1 and MV-2 appear to contain a single, circular chromosome. Genome sizes of strains MV-1, MV-2, and MC-1 were estimated to be between 3.6 and 3.9 Mb (mean +/- SD; 3.7 +/- 0.2), 3. 3 and 3.7 Mb (3.6 +/- 0.2), and 4.3 and 4.7 Mb (4.5 +/- 0.3), respectively. The restriction fragment patterns of the vibrioid strains MV-1 and MV-2 were extremely similar, suggesting that the strains are closely related.

DNA Restriction Enzymes↗
PubMed1999

Improved technique for the isolation of magnetotactic spirilla from a freshwater sediment and their phylogenetic characterization.

An improved technique for the isolation of magnetotactic bacteria was used for the axenic cultivation of microaerophilic magnetotactic spirilla. Magnetotactic bacteria were first separated from non-magnetic contaminants by exploiting their active migration along magnetic field lines by a capillary "racetrack" method. The purified magnetic cells were then inoculated into a two-layer isolation medium with opposing oxygen and sulfide gradients. Several strains of magnetotactic spirilla were isolated from a freshwater sediment sample using this method. Based on their morphology, physiology and comparative analysis of almost complete 16S rRNA gene sequences, all newly isolated strains were identified as members of the genus Magnetospirillum. While five of the isolates were closely related to previously described species (> 99% sequence similarity), two isolates appear to represent a third phylogenetic cluster within the genus Magnetospirillum.

Bacteria↗
PubMed1999

Synthesis of the bacterial magnetosome: the making of a magnetic personality.

Magnetotactic bacteria synthesize intracellular, enveloped, single magnetic domain crystals of magnetite (Fe3O4, Fe2+Fe2(3+)O4) and/or greigite (Fe3S4) called magnetosomes. The magnetosomes contain well-ordered crystals that have narrow size distributions and consistent species- and/or strain-specific morphologies. These characteristics are features of a process called biologically-controlled mineralization in which an organism exerts a great degree of crystallochemical control over the nucleation and growth of the mineral particle. Because of these features, the mineral particles have been used as biomarkers although not without controversy. These unique structures impart a permanent magnetic dipole moment to the cell causing it to align and swim along geomagnetic field lines, a behavior known as magnetotaxis. The apparent biological advantage of magnetotaxis is that it aids cells in more efficiently locating and maintaining position in vertical chemical gradients common in many natural aquatic environments.

Bacteria↗
PubMed1998

Reaction sequence of iron sulfide minerals in bacteria and their use as biomarkers.

Some bacteria form intracellular nanometer-scale crystals of greigite (Fe3S4) that cause the bacteria to be oriented in magnetic fields. Transmission electron microscope observations showed that ferrimagnetic greigite in these bacteria forms from nonmagnetic mackinawite (tetragonal FeS) and possibly from cubic FeS. These precursors apparently transform into greigite by rearrangement of iron atoms over a period of days to weeks. Neither pyrrhotite nor pyrite was found. These results have implications for the interpretation of the presence of pyrrhotite and greigite in the martian meteorite ALH84001.

Bacteria↗
PubMed1997

Magneto-aerotaxis in marine coccoid bacteria.

Magnetotactic cocci swim persistently along local magnetic field lines in a preferred direction that corresponds to downward migration along geomagnetic field lines. Recently, high cell concentrations of magnetotactic cocci have been found in the water columns of chemically stratified, marine and brackish habitats, and not always in the sediments, as would be expected for persistent, downward-migrating bacteria. Here we report that cells of a pure culture of a marine magnetotactic coccus, designated strain MC-1, formed microaerophilic bands in capillary tubes and used aerotaxis to migrate to a preferred oxygen concentration in an oxygen gradient. Cells were able to swim in either direction along the local magnetic field and used magnetotaxis in conjunction with aerotaxis, i.e., magnetically assisted aerotaxis, or magneto-aerotaxis, to more efficiently migrate to and maintain position at their preferred oxygen concentration. Cells of strain MC-1 had a novel, aerotactic sensory mechanism that appeared to function as a two-way switch, rather than the temporal sensory mechanism used by other bacteria, including Magnetospirillum megnetotacticum, in aerotaxis. The cells also exhibited a response to short-wavelength light (< or = 500 nm), which caused them to swim persistently parallel to the magnetic field during illumination.

Cell Movement↗
PubMed1995

Controlled Biomineralization of Magnetite (Fe(inf3)O(inf4)) and Greigite (Fe(inf3)S(inf4)) in a Magnetotactic Bacterium.

A slowly moving, rod-shaped magnetotactic bacterium was found in relatively large numbers at and below the oxic-anoxic transition zone of a semianaerobic estuarine basin. Unlike all magnetotactic bacteria described to date, cells of this organism produce single-magnetic-domain particles of an iron oxide, magnetite (Fe(inf3)O(inf4)), and an iron sulfide, greigite (Fe(inf3)S(inf4)), within their magnetosomes. The crystals had different morphologies, being arrowhead or tooth shaped for the magnetite particles and roughly rectangular for the greigite particles, and were coorganized within the same chain(s) in the same cell with their long axes along the chain direction. Because the two crystal types have different crystallochemical characteristics, the findings presented here suggest that the formation of the crystal types is controlled by separate biomineralization processes and that the assembly of the magnetosome chain is controlled by a third ultrastructural process. In addition, our results show that in some magnetotactic bacteria, external environmental conditions such as redox and/or oxygen or hydrogen sulfide concentrations may affect the composition of the nonmetal part of the magnetosome mineral phase.

Journal Article↗
PubMed1994

Electron microscopic studies of magnetosomes in magnetotactic bacteria.

Electron microscopic studies on magnetosomes in magnetotactic bacteria have revealed much information on their composition, structure, and even the formation of their mineral phase. The mineral phases of the magnetosomes are of two general types: iron oxides and iron sulfides. Iron oxide-type magnetosomes contain particles of the ferrimagnetic mineral magnetite (Fe3O4) while the iron sulfide-type contain ferrimagnetic greigite (Fe3S4), greigite and non-magnetic pyrite (FeS2), or possibly ferrimagnetic pyrrhotite (Fe7S8). Regardless of their composition, the crystalline particles in magnetosomes have a narrow size range: approximately 35 to 120 nm. Magnetite crystals in this size range are single-magnetic-domains and confer a permanent magnetic dipole moment to the cell. The single-domain size range for greigite is not known but is probably similar to that for magnetite. The morphology of the particles in the bacterial magnetosomes appears to be species-specific. Morphologies of magnetite crystals in different species of magnetotactic bacteria include cubo-octahedra, parallelepipedal (truncated hexahedral or octahedral prisms), and tooth- or bullet-shaped (anisotropic). Morphologies of greigite particles include cubo-octahedra and rectangular prismatic. The greigite-pyrite particles are generally pleomorphic with no consistent crystalline morphology. A membrane has been shown to surround the particles in some organisms and may be involved in the formation of the crystalline phase while also providing physical constraints on the size and the shape of the crystal. These results clearly indicate that the biomineralization process involved in the bacterial magnetosome, a good example of a self-assembled structure on a nanometer scale, is highly controlled by the organism.

Bacteria↗
PubMed1989

Microbial utilization of naturally occurring hydrocarbons at the guaymas basin hydrothermal vent site.

The Guaymas Basin (Gulf of California; depth, 2,000 m) is a site of hydrothermal activity in which petroliferous material is formed by thermal alteration of deposited planktonic and terrestrial organic matter. We investigated certain components of these naturally occurring hydrocarbons as potential carbon sources for a specific microflora at these deep-sea vent sites. Respiratory conversion of [1-C]hexadecane and [1(4,5,8)-C]naphthalene to CO(2) was observed at 4 degrees C and 25 degrees C, and some was observed at 55 degrees C, but none was observed at 80 degrees C. Bacterial isolates were capable of growing on both substrates as the sole carbon source. All isolates were aerobic and mesophilic with respect to growth on hydrocarbons but also grew at low temperatures (4 to 5 degrees C). These results correlate well with previous geochemical analyses, indicating microbial hydrocarbon degradation, and show that at least some of the thermally produced hydrocarbons at Guaymas Basin are significant carbon sources to vent microbiota.

Journal Article↗
PubMed1987

Decomposition of hydroxylamine by hemoglobin.

The reaction between hydroxylamine (NH2OH) and human hemoglobin (Hb) at pH 6-8 and the reaction between NH2OH and methemoglobin (Hb+) chiefly at pH 7 were studied under anaerobic conditions at 25 degrees C. In presence of cyanide, which was used to trap Hb+, Hb was oxidized by NH2OH to methemoglobin cyanide with production of about 0.5 mol NH+4/mol of heme oxidized at pH 7. The conversion of Hb to Hb+ was first order in [Hb] (or nearly so) but the pseudo-first-order rate constant was not strictly proportional to [NH2OH]. Thus, the apparent second-order rate constant at pH 7 decreased from about 30 M-1 X s-1 to a limiting value of 11.3 M-1 X s-1 with increasing [NH2OH]. The rate of Hb oxidation was not much affected by cyanide, whereas there was no reaction between NH2OH and carbonmonoxyhemoglobin (HbCO). The pseudo-first-order rate constant for Hb oxidation at 500 microM NH2OH increased from about 0.008 s-1 at pH 6 to 0.02 s-1 at pH 8. The oxidation of Hb by NH2OH terminated prematurely at 75-90% completion at pH 7 and at 30-35% completion at pH 8. Data on the premature termination of reaction fit the titration curve for a group with pK = 7.5-7.7. NH2OH was decomposed by Hb+ to N2, NH+4, and a small amount of N2O in what appears to be a dismutation reaction. Nitrite and hydrazine were not detected, and N2 and NH+4 were produced in nearly equimolar amounts. The dismutation reaction was first order in [Hb+] and [NH2OH] only at low concentrations of reactants and was cleanly inhibited by cyanide. The spectrum of Hb+ remained unchanged during the reaction, except for the gradual formation of some choleglobin-like (green) pigment, whereas in the presence of CO, HbCO was formed. Kinetics are consistent with the view advanced previously by J. S. Colter and J. H. Quastel [1950) Arch. Biochem. 27, 368-389) that the decomposition of NH2OH proceeds by a mechanism involving a Hb/Hb+ cycle (reactions [1] and [2]) in which Hb is oxidized to Hb+ by NH2OH.

Hemoglobins↗
PubMed1987

Loss of N2O reductase activity as an explanation for poor growth of Pseudomonas aeruginosa on N2O.

N2O uptake activity of cells and N2O reductase activity of the soluble fraction from denitrifying bacteria were assayed. Pseudomonas aeruginosa strains PAO1 and P1 lost most of their N2O uptake activity and the ability to grow well on N2O within 2 to 5 h after exposure to N2O. Extensive loss of N2O reductase activity accompanied the nearly complete loss of N2O uptake activity under N2O. Paracoccus denitrificans retained much, but not all, of both activities and the ability to grow vigorously on N2O. The pattern with P. aeruginosa strain P2 resembled that for PAO1 and P1 except that loss of the activities proceeded at a slower rate and growth could continue for up to 12 h after exposure to N2O. The inability of a number of P. aeruginosa strains to grow well on N2O is therefore a direct consequence of the nearly complete loss of N2O reductase activity. Turnover-dependent inactivation of N2O reductase and its reactivation under reducing conditions occurred in vitro for the enzyme from P. aeruginosa and Paracoccus denitrificans. These events may be significant in determining the activity level of N2O reductase in denitrifying bacteria during N2O respiration.

Enzyme Activation↗
PubMed1986

Growth of Pseudomonas aeruginosa on nitrous oxide.

Three strains of Pseudomonas aeruginosa were grown anaerobically on exogenous N2O in a defined medium under conditions that assured the maintenance of highly anaerobic conditions for periods of 1 week or more. The bacteria were observed reproducibly to increase their cell density by factors of 3 to 9, but not more, depending on the initial amount of N2O. Growth on N2O was cleanly blocked by acetylene. Cell yields, CO2 production, and N2O uptake all increased with initial PN2O at PN2O less than or equal to 0.1 atm. Growth curves were atypical in the sense that growth rates decreased with time. This is the first observation of growth of P. aeruginosa on N2O as the sole oxidant. N2O was shown to be an obligatory, freely diffusible intermediate during growth of strains PAO1 and P1 on nitrate. All three strains used this endogenous N2O efficiently for growth. For strains PAO1 and P1, it was confirmed that exogenous N2O had little effect on the cell yields of cultures growing with nitrate; thus, for these strains exogenous N2O neither directly inhibited growth nor was used significantly for growth. On the other hand, strain P2 grew abundantly on exogenous N2O when small and growth-limiting concentrations of nitrate or nitrate (2 to 10 mM) were included in the medium. The dramatic effect of these N-anions was realized in large part even when the exogenous N2O was introduced immediately after the quantitative conversion of anion-nitrogen to N2. No evidence was found for a factor in filter-sterilized spent medium that stimulated fresh inocula to grow abundantly on N2O.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobiosis↗
PubMed1986

Denitrification by Chromobacterium violaceum.

One host (Rana catesbiana)-associated and two free-living mesophilic strains of bacteria with violet pigmentation and biochemical characteristics of Chromobacterium violaceum were isolated from freshwater habitats. Cells of each freshly isolated strain and of strain ATCC 12472 (the neotype strain) grew anaerobically with glucose as the sole carbon and energy source. The major fermentation products of cells grown in Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) supplemented with glucose included acetate, small amounts of propionate, lactate, and pyruvate. The final cell yield and culture growth rate of each strain cultured anaerobically in this medium increased approximately twofold with the addition of 2 mM NaNO(3). Final growth yields increased in direct proportion to the quantity of added NaNO(3) over the range of 0.5 to 5 mM. Each strain reduced NO(3), producing NO(2), NO, and N(2)O. NO(2) accumulated transiently. With 2 mM NaNO(3) in the medium, N(2)O made up 85 to 98% of the N product recovered with each strain. N-oxides were recovered in the same quantity and distribution whether 0.01 atm (ca. 1 kPa) of C(2)H(2) (added to block N(2)O reduction) was present or not. Neither N(2) production nor gas accumulation was detected during NO(3) reduction by growing cells. Cell growth in media containing 0.5 to 5 mM NaNO(2) in lieu of NaNO(3) was delayed, and although N(2)O was produced by the end of growth, NO(2) -containing media did not support growth to an extent greater than did medium lacking NO(3) or NO(2). The data indicate that C. violaceum cells ferment glucose or denitrify, terminating denitrification with the production of N(2)O, and that NO(2) reduction to N(2)O is not coupled to growth but may serve as a detoxification mechanism. No strain detectably fixed N(2) (reduced C(2)H(2)).

Journal Article↗
PubMed1983

Denitrification and Assimilatory Nitrate Reduction in Aquaspirillum magnetotacticum.

Aquaspirillum magnetotacticum MS-1 grew microaerobically but not anaerobically with NO(3) or NH(4) as the sole nitrogen source. Nevertheless, cell yields varied directly with NO(3) concentration under microaerobic conditions. Products of NO(3) reduction included NH(4), N(2)O, NO, and N(2). NO(2) and NH(2)OH, each toxic to cells at 0.2 mM, were not detected as products of cells growing on NO(3). NO(3) reduction to NH(4) was completely repressed by the addition of 2 mM NH(4) to the growth medium, whereas NO(3) reduction to N(2)O or to N(2) was not. C(2)H(2) completely inhibited N(2)O reduction to N(2) by growing cells. These results indicate that A. magnetotacticum is a microaerophilic denitrifier that is versatile in its nitrogen metabolism, concomitantly reducing NO(3) by assimilatory and dissimilatory means. This bacterium appears to be the first described denitrifier with an absolute requirement for O(2). The process of NO(3) reduction appears well adapted for avoiding accumulation of several nitrogenous intermediates that are toxic to cells.

Journal Article↗