Bacterial actin MreB assembles in complex with cell shape protein RodZ.

Bacterial actin MreB assembles in complex with cell shape protein RodZ.: "

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Bacterial actin MreB assembles in complex with cell shape protein RodZ.

EMBO J. 2010 Feb 18;

Authors: van den Ent F, Johnson CM, Persons L, de Boer P, Löwe J

Bacterial actin homologue MreB is required for cell shape maintenance in most non-spherical bacteria, where it assembles into helical structures just underneath the cytoplasmic membrane. Proper assembly of the actin cytoskeleton requires RodZ, a conserved, bitopic membrane protein that colocalises to MreB and is essential for cell shape determination. Here, we present the first crystal structure of bacterial actin engaged with a natural partner and provide a clear functional significance of the interaction. We show that the cytoplasmic helix-turn-helix motif of Thermotoga maritima RodZ directly interacts with monomeric as well as filamentous MreB and present the crystal structure of the complex. In vitro and in vivo analyses of mutant T. maritima and Escherichia coli RodZ validate the structure and reveal the importance of the MreB-RodZ interaction in the ability of cells to propagate as rods. Furthermore, the results elucidate how the bacterial actin cytoskeleton might be anchored to the membrane to help constrain peptidoglycan synthesis in the periplasm.

PMID: 20168300 [PubMed - as supplied by publisher]

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Organic-walled microfossils in 3.2-billion-year-old shallow-marine siliciclastic deposits.

 Although the notion of an early origin and diversification of life on Earth during the Archaean eon has received
increasing support in geochemical, sedimentological and palaeontological evidence, ambiguities and
controversies persist regarding the biogenicity and syngeneity of the record older than Late Archaean.

Non-biological processes are known to produce morphologies similar to some microfossils, and hydrothermal fluids have the potential to produce abiotic organic compounds with depleted carbon isotope values, making it difficult to establish unambiguous traces of life. Here we report the discovery of a population of large (up to about 300 μm in diameter) carbonaceous spheroidal microstructures in Mesoarchaean shales and siltstones of the Moodies Group, South Africa, the Earth’s oldest siliciclastic alluvial to tidal-estuarine deposits. These microstructures are interpreted as organic-walled microfossils on the basis of petrographic and geochemical evidence for their endogenicity and syngeneity, their carbonaceous composition, cellular morphology and ultrastructure, occurrence in populations, taphonomic features of soft wall deformation, and the geological context plausible for life, as well as a lack of abiotic explanation falsifying a biological origin. These are the oldest and largest Archaean organic-walled spheroidal microfossils reported so far. Our observations suggest that relatively large microorganisms cohabited with earlier reported benthic microbial matsin the photic zone of marginal marine siliciclastic environments 3.2 billion years ago.

Javaux, Emmanuelle J., Craig P. Marshall, y Andrey Bekker. 2010. Organic-walled microfossils in 3.2-billion-year-old shallow-marine siliciclastic deposits. Nature 463, no. 7283 (Febrero 18): 934-938. 

doi:10.1038/nature08793. http://dx.doi.org/10.1038/nature08793. 

Secuenciado el genoma de un hombre de hace 4000 años

Ancient human genome sequence of an extinct Palaeo-Eskimo.

We report here the genome sequence of an ancient human. Obtained from ~4,000-year-old permafrost-preserved hair, the genome represents a male individual from the first known culture to settle in Greenland. Sequenced to an average depth of 20×, we recover 79% of the diploid genome, an amount close to the practical limit of current sequencing technologies. We identify 353,151 high-confidence single-nucleotide polymorphisms (SNPs), of which 6.8% have not been reported previously. We estimate raw read contamination to be no higher than 0.8%. We use functional SNP assessment to assign possible phenotypic characteristics of the individual that belonged to a culture whose location has yielded only trace human remains. We compare the high-confidence SNPs to those of contemporary populations to find the populations most closely related to the individual. This provides evidence for a migration from Siberia into the New World some 5,500 years ago, independent of that giving rise to the modern Native Americans and Inuit

Nature 463, 757-762 (11 February 2010) | doi:10.1038/nature08835; Received 30 November 2009; Accepted 18 January 2010

Enlace al trabajo

More than 9,000,000 unique genes in human gut bacterial community: estimating gene numbers inside a human body.

More than 9,000,000 unique genes in human gut bacterial community: estimating gene numbers inside a human body.: "

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More than 9,000,000 unique genes in human gut bacterial community: estimating gene numbers inside a human body.

PLoS One. 2009;4(6):e6074

Authors: Yang X, Xie L, Li Y, Wei C

BACKGROUND: Estimating the number of genes in human genome has been long an important problem in computational biology. With the new conception of considering human as a super-organism, it is also interesting to estimate the number of genes in this human super-organism. PRINCIPAL FINDINGS: We presented our estimation of gene numbers in the human gut bacterial community, the largest microbial community inside the human super-organism. We got 552,700 unique genes from 202 complete human gut bacteria genomes. Then, a novel gene counting model was built to check the total number of genes by combining culture-independent sequence data and those complete genomes. 16S rRNAs were used to construct a three-level tree and different counting methods were introduced for the three levels: strain-to-species, species-to-genus, and genus-and-up. The model estimates that the total number of genes is about 9,000,000 after those with identity percentage of 97% or up were merged. CONCLUSION: By combining completed genomes currently available and culture-independent sequencing data, we built a model to estimate the number of genes in human gut bacterial community. The total number of genes is estimated to be about 9 million. Although this number is huge, we believe it is underestimated. This is an initial step to tackle this gene counting problem for the human super-organism. It will still be an open problem in the near future. The list of genomes used in this paper can be found in the supplementary table.

PMID: 19562079 [PubMed - indexed for MEDLINE]

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Movilidad en mixobacterias

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Bacterial motility complexes require the actin-like protein, MreB and the Ras homologue, MglA.

EMBO J. 2010 Jan 20;29(2):315-26

Authors: Mauriello EM, Mouhamar F, Nan B, Ducret A, Dai D, Zusman DR, Mignot T

Gliding motility in the bacterium Myxococcus xanthus uses two motility engines: S-motility powered by type-IV pili and A-motility powered by uncharacterized motor proteins and focal adhesion complexes. In this paper, we identified MreB, an actin-like protein, and MglA, a small GTPase of the Ras superfamily, as essential for both motility systems. A22, an inhibitor of MreB cytoskeleton assembly, reversibly inhibited S- and A-motility, causing rapid dispersal of S- and A-motility protein clusters, FrzS and AglZ. This suggests that the MreB cytoskeleton is involved in directing the positioning of these proteins. We also found that a DeltamglA motility mutant showed defective localization of AglZ and FrzS clusters. Interestingly, MglA-YFP localization mimicked both FrzS and AglZ patterns and was perturbed by A22 treatment, consistent with results indicating that both MglA and MreB bind to motility complexes. We propose that MglA and the MreB cytoskeleton act together in a pathway to localize motility proteins such as AglZ and FrzS to assemble the A-motility machineries. Interestingly, M. xanthus motility systems, like eukaryotic systems, use an actin-like protein and a small GTPase spatial regulator.

Deletion of the ftsZ-like Gene Results in the Production of Superparamagnetic Magnetite Magnetosomes in Magnetospirillum gryphiswaldense.

En las bacterias magnetotácticas hay dos genes: uno que codifican para la proteína de división celualr FtsZ y otro gen que codifica para una proteína similar a FtsZ. Esta segunda proteína similar a FtsZ está implicada en la formación de magnetosomas



Deletion of the ftsZ-like Gene Results in the Production of Superparamagnetic Magnetite Magnetosomes in Magnetospirillum gryphiswaldense.

J Bacteriol. 2009 Dec 18;

Authors: Ding Y, Li J, Liu J, Yang J, Jiang W, Tian J, Li Y, Pan Y, Li J

Magnetotactic bacteria (MTB) synthesize unique organelles termed 'magnetosomes', which are membrane-enclosed structures containing crystals of magnetite or greigite. Magnetosomes form a chain around MamK cytoskeletal filaments, and provide the basis for the ability of MTB to navigate along geomagnetic field lines, to find optimal microaerobic habitats. Genomes of species of the MTB genus Magnetospirillum, in addition to a gene encoding the tubulin-like FtsZ protein (involved in cell division), contain a second gene termed 'ftsZ-like', whose function is unknown. In the present study, we found that the ftsZ-like gene of M. gryphiswaldense strain MSR-1 belongs to 4.9-kb mamXY polycistronic transcription unit. We then purified recombinant FtsZ-like protein to homogeneity. FtsZ-like efficiently hydrolyzed ATP and GTP, with ATPase and GTPase activities of 2.17 and 5.56 mumol phosphorus per mol protein per min respectively. FtsZ-like underwent GTP-dependent polymerization into long filamentous bundles in vitro. To determine the role of ftsZ-like, we constructed a mutant of ftsZ-like (DeltaftsZ-like), and its complementation strain (DeltaftsZ-like_C). Growth of DeltaftsZ-like cells was similar to that of wild-type, indicating that DeltaftsZ-like gene is not involved in cell division. Transmission electron microscopic observations indicated that the DeltaftsZ-like cells, in comparison to wild-type, produced smaller magnetosomes, with poorly-defined morphology, and irregular alignment including large gaps. Magnetic analyses showed that DeltaftsZ-like produced mainly superparamagnetic (SP) magnetite particles, whereas wide-type and DeltaftsZ-like_C cells produced mainly single-domain (SD) particles. Our findings suggest that the FtsZ-like protein is required for synthesis of SD particles and of magnetosomes in M. gryphiswaldense.