Controlled biomineralization of magnetite (Fe₃O₄) by <i>Magnetospirillum gryphiswaldense</i>

Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (∼14-67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range

NITROGEN METABOLISM AND IRON REDUCTION IN AQUASPIRILLUM MAGNETOTACTICUM (NITRATE, FIXATION, MAGNETIC BACTERIUM)

Aquaspirillum magnetotacticum strain MS-1 grew microaerobically but not anaerobically with NO(,3)(\u27-) or NH(,4)(\u27+) as the sole nitrogen source. Cell yields varied directly with NO(,3)(\u27-) concentration under microaerobic conditions. Products of NO(,3)(\u27-) reduction by growing cells included NH(,4)(\u27+), N(,2)O, NO, and N(,2) but not NO(,2)(\u27-) or NH(,2)OH. The inclusion of NH(,4)(\u27+) in growth medium prevented NO(,3)(\u27-) reduction to NH(,4)(\u27+) but not to N(,2)O or N(,2). Cells consumed O(,2) while denitrifying and this appears to be the first described species with an absolute requirement for O(,2) while denitrifying. Cultures grown with NO(,3)(\u27-), in contrast to NH(,4)(\u27+), contained fewer cells without magnetosomes. Moreover, among the cells with these intracellular magnetic particles, a higher average number per cell and a higher average cell magnetic moment was obtained with NO(,3)(\u27-). This effect of cell nitrogen source on culture magnetism was investigated further with growing cells and cell-free extracts. The results indicated that Fe(\u27+3) reduction by cell-free extracts of A. magnetotacticum was independent of electron transport chain components and suggested that Fe(\u27+3) and NO(,3)(\u27-) reduction proceeded independently in the cell. A. magnetotacticum strain MS-1 and several non-magnetic mutants derived from it, fixed N(,2) (reduced acetylene) microaerobically but not anaerobically even with NO(,3)(\u27-). Cells of A. magnetotacticum reduced acetylene at rates comparable to those of Azospirillum lipoferum under similar conditions but at a much lower rate than that of Azotobacter vinelandii grown aerobically

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

Magnetotactic bacteria synthesize intracellular, enveloped, single magnetic domain crystals of magnetite Fe3O4, Fe2+Fe23+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

Magnetic irreversibility and Verwey transition in nano-crystalline bacterial magnetite

The magnetic properties of biologically-produced magnetite nanocrystals biomineralized by four different magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high quality single crystals. The magnetic feature at the Verwey temperature, $T_{V}$, was clearly seen in all nanocrystals, although its sharpness depended on the shape of individual nanoparticles and whether or not the particles were arranged in magnetosome chains. The transition was broader in the individual superparamagnetic nanoparticles for which $T_{B}<T_{V}$, where $T_{B}$ is the superparamagnetic blocking temperature. For the nanocrystals organized in chains, the effective blocking temperature $T_{B}>T_{V}$ and the Verwey transition is sharply defined. No correlation between the particle size and $T_{V}$ was found. Furthermore, measurements of $M(H,T,time)$ suggest that magnetosome chains behave as long magnetic dipoles where the local magnetic field is directed along the chain and this result confirms that time-logarithmic magnetic relaxation is due to the collective (dipolar) nature of the barrier for magnetic moment reorientation

Magnetotaxis and Magnetic Particles in Bacteria

Magnetotactic bacteria contain magnetic particles that constitute a permanent magnetic dipole and cause each cell to orient and migrate along geomagnetic field lines. Recent results relevant to the biomineralization process and to the function of magnetotaxis are discussed

Magnetosome genes in the Gammaproteobacterium strain BW-2

Magnetotactic bacteria (MTB) biomineralize intracellular nanometer-sized, magnetic crystals surrounded by a lipid bilayer membrane known as magnetosomes. These crystals, which consist of magnetite (Fe3O4) or greigite (Fe3S4), causes the cell to align along the geomagnetic field lines as they swim, a phenomenon known as magnetotaxis. Strain BW-2 is a magnetite-producing magnetotactic bacterium isolated from Badwater Basin, Death Valley National Park (California) and is one of only two species of MTB that are known to phylogenetically belong to the Gammaproteobacteria class of the Proteobacteria phylum. The biomineralization of magnetite in magnetotactic bacteria is mediated by a series of genes that include the mam, mms, and mtx genes that presumably control the production of and the size and shape of the magnetite crystal within the magnetosomes. Magnetosome genes have not yet been found in the genomes of newly discovered magnetotactic Gammaproteobacteria. In this study, we use polymerase chain reaction with degenerate primers designed from mam genes found in other MTB, and DNA sequencing to search for and amplify possible mam genes in the Gammaproteobacterium strain BW-2. In addition, with enough DNA sequence, we may be able to find evidence of the presence of a magnetosome gene island in this organism. Positive results from this study will be instrumental in determining evidence for lateral gene transfer of the magnetosome gene island to the Gammaproteobacteria and the evolution of magnetotaxis based on magnetite biomineralization in general

Phylogenetic studies of newly isolated freshwater Magnetospirilla using cbb and mam genes

The phylogeny and general relatedness of prokaryotes is determined by comparisons of the sequences of rRNA genes, most commonly the 16S rRNA gene. Comparisons between other gene sequences have been used for this purpose and some have supported conclusions from 16S rRNA genes while others have not. In this study, 13 new magnetospirilla were phylogenetically characterized using the sequences of the 16S rRNA gene as well as the genes for forms I and II ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) (cbbL and cbbM, respectively) and for two magnetosome membrane proteins unique to magnetotactic bacteria, mamJ and mamK. Polymerase chain reaction (PCR) with degenerate primers designed for the specific genes under study was used to amplify a large portion of the genes. PCR products were cloned and sequenced and used for the construction of phylogenetic trees. Based on 16S rRNA gene sequences, the magnetospirilla phylogenetically span, more as a continuum rather than as clearly delineated groups, over two genera based on the current accepted sequence divergence between organisms for genera (\u3e5%). While almost all strains appear to fit into the genus Magnetospirillum, strain LM-1 appears to represent a new genus. Phylogeny of these strains based on cbbM sequences was reasonably consistent with that from 16S rRNA genes. The cbbL gene was not a good choice for this study as most strains did not possess this gene. Relatedness and phylogeny of the strains based on mamJ and mamK sequences was more complex. Although our data set is not complete, some specific strains shown to be closely related by 16S rRNA gene sequence, also appeared to be closely related based on one or both of the mam gene sequences (e.g., strains UT-1, LM-2 and M. gryphiswaldense strain MSR-1). Other strains did not show this type of relationship. Because of these somewhat inconsistent results, those from mam gene sequences might reflect evolution of the magnetosome gene island (MAI) in magnetospirilla rather than relatedness between strains

Water Use in Las Vegas

How Much Water Does Las Vegas Use? Water Use Per Capita The average household in Southern Nevada uses about 222 gallons of water per day. This has recently dropped from using 314 gallons of water per day. The southern Nevada Water Authority hopes that by the year 2035, water use will have dropped down to 199 gallons per day for each household. The majority of Southern Nevada’s water goes to residential use, both indoor and outdoor. Because of this, restrictions have been placed on certain aspects of water use such as the amount of lawn a household can own. Aside from residential use, a large amount of water is still used in other areas of communities, such as golf courses. A golf course can use up to 6.3 acre-feet of water per acre of land without penalty. That’s over 2 million gallons of water for each acre per year

Biomineralization of Magnetic Iron Minerals in Bacteria

Magnetotactic bacteria orient and migrate along magnetic field lines. This ability is based on a submicron assembly of single-magnetic domain iron mineral particles that elegantly solves the problem of how to construct a magnetic dipole that is large enough to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized cell. The solution is based on the ability of the bacteria to accumulate high concentrations of iron, and control the deposition, size and orientation of a specific iron mineral at specific locations in the cell