Copper association with iron sulfide magnetosomes in a magnetotactic bacterium

Greigite (Fe₃S₄) and pyrite (FeS₂) particles in the magnetosomes of a many-celled, magnetotactic prokaryote (MMP), common in brackish-to-marine, sulfidic, aquatic habitats, contained relatively high concentrations of copper which ranged from about 0.1 to 10 atomic per cent relative to iron. In contrast, the greigite particles in the magnetosomes of a curved magnetotactic bacterium collected from the same sampling site did not contain significant levels of copper. The ability of the MMP to biomineralize copper within its magnetosomes appeared to be limited to that organism and dependent upon the site from which it was collected. Although the chemical mechanism and physiological function of copper accumulation in the magnetosomes of the MMP is unclear, the presence of copper is the first evidence that another transition metal ion could be incorporated in the mineral phase of the magnetosomes of a magnetotactic bacterium.Abbreviation MMP many-celled magnetotactic prokaryote     

Isolation of magnetotactic bacterium WM-1 from freshwater sediment and phylogenetic characterization

The magnetotactic bacterium was isolated from freshwater sediment from North Lake of Wuhan. The isolate, designated WM-1, was Gram-negative, helical shaped, and studied by means of electron microscopy. The strain WM-1 was 0.2-0.4 μm in diameter and 3–4 μm in length. The DNA G + C content was found to be 65.7 mol%. Phylogenetic analysis of the 16S rDNA gene (Accession number DQ899734 in GeneBank) revealed that this isolate was a member ofαsubdivision of the Proteobacteria. Strain WM-1 was closely related (97.7%) to Magnetospirillum sp. AMB-1. Randomly amplified polymorphic DNA analysis showed that these two strains were in fact different strains. Electron diffraction patterns of WM-1 magnetosomes indicated that the magnetosomes were composed of magnetite. The magnetosomes from WM-1 were cuboidal in shape as observed by electron microscopy. Statistical analysis of magnetite crystals from WM-1 showed narrow asymmetric size distribution. The average number of magnetosomes in each WM-1 bacterium was 8 ± 3.4. The average length of magnetosomes in WM-1 was 54 ± 12.3 nm and the average width is 43 ± 10.9 nm. These data showed that the grains in WM-1 were single-domain crystals.     

趋磁细菌磁小体合成机制研究进展

趋磁细菌可在环境中吸收大量铁并在细胞内合成纳米级磁性颗粒—磁小体。比较几种趋磁细菌基因组特征,针对磁小体岛及与磁小体合成相关基因功能特点等方面,综述了当前磁小体合成机制的研究进展。     

A <Emphasis Type="Italic">Magnetospirillum</Emphasis> strain WM-1 from a freshwater sediment with intracellular magnetosomes

Summary A helical shaped bacterium capable of producing magnetosomes, designated WM-1, was isolated from freshwater sediment through an improved isolated method that combined magnetic separation and the “race track” method. The strain WM-1 was Gram-negative, 0.2–0.4 μm in diameter and 3–4 μm in length. The strain WM-1 was identified as genus Magnetospirillum in the α-Proteobacteria according to the sequence analysis of the 16S rDNA, the morphology and physiological characteristics. The shape of the magnetosomes in WM-1was cuboidal by electron microscopy. Statistical analysis of WM-1 magnetosome crystals showed that the average number of magnetosomes in a WM-1 bacterium was 8 ± 3.4, and the average length was 54 ± 12.3 nm, and the average width was 43 ± 10.9 nm.     

Desulfamplus magnetovallimortis gen. nov., sp. nov., a magnetotactic bacterium from a brackish desert spring able to biomineralize greigite and magnetite,that represents a novel lineage in the Desulfobacteraceae

A magnetotactic bacterium, designated strain BW-1^T, was isolated from a brackish spring in Death Valley National Park (California, USA) and cultivated in axenic culture. The Gram-negative cells of strain BW-1^T are relatively large and rod-shaped and possess a single polar flagellum (monotrichous). This strain is the first magnetotactic bacterium isolated in axenic culture capable of producing greigite and/or magnetite nanocrystals aligned in one or more chains per cell. Strain BW-1^T is an obligate anaerobe that grows chemoorganoheterotrophically while reducing sulfate as a terminal electron acceptor. Optimal growth occurred at pH 7.0 and 28 °C with fumarate as electron donor and carbon source. Based on its genome sequence, the G + C content is 40.72 mol %. Phylogenomic and phylogenetic analyses indicate that strain BW-1^T belongs to the Desulfobacteraceae family within the Deltaproteobacteria class. Based on average amino acid identity, strain BW-1^T can be considered as a novel species of a new genus, for which the name Desulfamplus magnetovallimortis is proposed. The type strain of D. magnetovallimortis is BW-1^T (JCM 18010^T–DSM 103535^T).     

Cytoplasmic ATPase involved in ferrous ion uptake from magnetotactic bacterium Magnetospirillum magneticum AMB-1

A non-magnetic mutant of Magnetospirillum magneticum AMB-1 (NMA61), harboring a defective gene located in ORF4 (gene ID: amb4111) was generated by transposon mutagenesis. Biochemical characterization of the gene product of ORF4 revealed that it was localized in the cytoplasm and displayed ATPase activity. The ability of NMA61 to take up iron was severely compromised. Ferrous ion concentration in the medium decreased more with the wild-type than with NMA61, while the iron content in the cytoplasmic fraction of NMA61 was much lower than the wild-type strain. This cytoplasmic ATPase is essential for iron trafficking within M. magneticum AMB-1.     

Proteomic analysis of Lactococcus lactis,a lactic acid bacterium

Lactococcus lactis is a Gram-positive bacteria, which belongs to the group of lactic acid bacteria among which several genera play an essential role in the manufacture of food products. Cytosolic proteins of L. lactis IL1403 cultivated in M17 broth have been resolved by two-dimensional gel electrophoresis using two pH gradients (pH 4-7, 4.5-5.5). More than 230 spots were identified by peptide mass fingerprints, corresponding to 25% of the predicted acid proteome. The present study made it possible to describe at the proteome level a significant number of cellular pathways (glycolysis, fermentation, nucleotide metabolism, proteolysis, fatty acid and peptidoglycan synthesis) related to important physiological processes and technological properties. It also indicated that the fermentative metabolism, which characterizes L. lactis is associated with a high expression of glycolytic enzymes. Thirty-four proteins were matched to open reading frames for which there is no assigned function. The comparison at the proteome level of two strains of L. lactis showed an important protein polymorphism. The comparison of the proteomes of glucose- and lactose-grown cells revealed an unexpected link between the nature of the carbon source and the metabolism of pyrimidine nucleotides.     

Measuring magnetosomal pH of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using pH-sensitive fluorescent proteins

Magnetotactic bacteria synthesize uniform-sized and regularly shaped magnetic nanoparticles in their organelles termed magnetosomes. Homeostasis of the magnetosome lumen must be maintained for its role accomplishment. Here, we developed a method to estimate the pH of a single living cell of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using a pH-sensitive fluorescent protein E²GFP. Using the pH measurement, we estimated that the cytoplasmic pH was approximately 7.6 and periplasmic pH was approximately 7.2. Moreover, we estimated pH in the magnetosome lumen and cytoplasmic surface using fusion proteins of E²GFP and magnetosome-associated proteins. The pH in the magnetosome lumen increased during the exponential growth phase when magnetotactic bacteria actively synthesize magnetite crystals, whereas pH at the magnetosome surface was not affected by the growth stage. This live-cell pH measurement method will help for understanding magnetosome pH homeostasis to reveal molecular mechanisms of magnetite biomineralization in the bacterial organelle.     

Carbon assimilation pathways in sulfate reducing bacteria. Formate,carbon dioxide,carbon monoxide,and acetate assimilation by Desulfovibrio baarsii

Desulfovibrio baarsii is a sulfate reducing bacterium, which can grown on formate plus sulfate as sole energy source and formate and CO₂ as sole carbon sources. It is shown by ¹⁴C labelling studies that more than 60% of the cell carbon is derived from CO₂ and the rest from formate. The cells thus grow autotrophically. Labelling studies with [¹⁴C]acetate, ¹⁴CO and [¹⁴C]formate indicate that CO₂ fixation does not proceed via the Calvin cycle. The labelling patterns of alanine, aspartate, glutamate, and glucosamine indicate that acetate (or activated acetic acid) is an early intermediate in formate and CO₂ assimilation; the methyl group of acetate is derived from formate, and the carboxyl group from CO₂ via CO; pyruvate is formed from acetyl-CoA by reductive carboxylation. The capacity to synthesize an acetate unit from two C₁-compounds obviously distinguishes D. baarsii from those Desulfovibrio species, which require acetate as a carbon source in addition to CO₂.     

Determination of the transmembrane proton gradient in the anaerobic bacterium Desulfovibrio desulfuricans by 31P nuclear magnetic resonance

The transmembrane proton gradient of the sulfate-reducing bacterium Desulfovibrio desulfuricans strain CSN has been determined by in vivo³¹P nuclear magnetic resonance (NMR) spectroscopy in the absence of dioxygen. At pH 7.0 in the medium (pH_ex) the intracellular pH (pH_in) was 7.5. By lowering pH_ex to 5.9 pH_in decreased to 7.1. At pH_ex greater than 7.7 the transmembrane proton gradient (pH) was zero. The uncouplers 3,3,4,5-tetrachlorosalicylanilide (TCS) and carbonylcyanide-m-chlorophenylhydrazone (CCCP), or the permeant anion thiocyanate caused complete dissipation of pH.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - TCS 3,3,4,5-tetrachlorosalicylanilide - MOPS 3-(N-morpholino)-propanesulfonic acid - P _i inorganic phosphate - pH _in (pH_ex) intracellular (extracellular) pH - pH transmembrane proton gradient (pH_in-pH_ex) - electrochemical membrane potential - chemical shift in parts per million - NMR nuclear magnetic resonance     

The genome of the Gram‐positive metal‐ and sulfate‐reducing bacterium Desulfotomaculum reducens strain MI‐1

Spore‐forming, Gram‐positive sulfate‐reducing bacteria (SRB) represent a group of SRB that dominates the deep subsurface as well as niches in which resistance to oxygen and dessication is an advantage. Desulfotomaculum reducens strain MI‐1 is one of the few cultured representatives of that group with a complete genome sequence available. The metabolic versatility of this organism is reflected in the presence of genes encoding for the oxidation of various electron donors, including three‐ and four‐carbon fatty acids and alcohols. Synteny in genes involved in sulfate reduction across all four sequenced Gram‐positive SRB suggests a distinct sulfate‐reduction mechanism for this group of bacteria. Based on the genomic information obtained for sulfate reduction in D. reducens, the transfer of electrons to the sulfite and APS reductases is proposed to take place via the quinone pool and heterodisulfide reductases respectively. In addition, both H₂‐evolving and H₂‐consuming cytoplasmic hydrogenases were identified in the genome, pointing to potential cytoplasmic H₂ cycling in the bacterium. The mechanism of metal reduction remains unknown.     

Identification of trehalose and glycine betaine as compatible solutes in the moderately halophilic sulfate reducing bacterium, Desulfovibrio halophilus

Abstract A gene ( ERG11 ) encoding cytochrome P450 sterol 14α-demethylase (P450_14DM) was isolated from the maize pathogen, Ustilago maydis , by amplifying part of the coding region of the gene using PCR and by employing the amplified DNA fragment as a hybridization probe to recover the complete gene from an U. maydis λEMBL3 genomic library. The deduced amino acid sequence of the U. maydis gene showed homology to P450_14DMs from other organisms and contained specific motifs which were hallmarks of P450s. Expression of the gene in an U. maydis mutant (A20) deficient in P450_14DM led to only a partial restoration of P450_14DM activity. Accumulation of ergosta-7,22-dienol and ergost-7-enol in A20 transformants containing the ERG11 gene implied that an additional mutation affecting sterol Δ ^5,6-desaturase activity accompanied the P450_14DM lesion.     

A gradient‐forming MipZ protein mediating the control of cell division in the magnetotactic bacterium Magnetospirillum gryphiswaldense

Cell division needs to be tightly regulated and closely coordinated with other cellular processes to ensure the generation of fully viable offspring. Here, we investigate division site placement by the cell division regulator MipZ in the alphaproteobacterium Magnetospirillum gryphiswaldense, a species that forms linear chains of magnetosomes to navigate within the geomagnetic field. We show that M. gryphiswaldense contains two MipZ homologs, termed MipZ1 and MipZ2. MipZ2 localizes to the division site, but its absence does not cause any obvious phenotype. MipZ1, by contrast, forms a dynamic bipolar gradient, and its deletion or overproduction cause cell filamentation, suggesting an important role in cell division. The monomeric form of MipZ1 interacts with the chromosome partitioning protein ParB, whereas its ATP‐dependent dimeric form shows non‐specific DNA‐binding activity. Notably, both the dimeric and, to a lesser extent, the monomeric form inhibit FtsZ polymerization in vitro. MipZ1 thus represents a canonical gradient‐forming MipZ homolog that critically contributes to the spatiotemporal control of FtsZ ring formation. Collectively, our findings add to the view that the regulatory role of MipZ proteins in cell division is conserved among many alphaproteobacteria. However, their number and biochemical properties may have adapted to the specific needs of the host organism.