The human gastric pathogen Helicobacter pylori has a potential acetone carboxylase that enhances its ability to colonize mice

<p>Abstract</p> <p>Background</p> <p><it>Helicobacter pylori </it>colonizes the human stomach and is the etiological agent of peptic ulcer disease. All three <it>H. pylori </it>strains that have been sequenced to date contain a potential operon whose products share homology with the subunits of acetone carboxylase (encoded by <it>acxABC</it>) from <it>Xanthobacter autotrophicus </it>strain Py2 and <it>Rhodobacter capsulatus </it>strain B10. Acetone carboxylase catalyzes the conversion of acetone to acetoacetate. Genes upstream of the putative <it>acxABC </it>operon encode enzymes that convert acetoacetate to acetoacetyl-CoA, which is metabolized further to generate two molecules of acetyl-CoA.</p> <p>Results</p> <p>To determine if the <it>H. pylori acxABC </it>operon has a role in host colonization the <it>acxB </it>homolog in the mouse-adapted <it>H. pylori </it>SS1 strain was inactivated with a chloramphenicol-resistance (<it>cat</it>) cassette. In mouse colonization studies the numbers of <it>H. pylori </it>recovered from mice inoculated with the <it>acxB:cat </it>mutant were generally one to two orders of magnitude lower than those recovered from mice inoculated with the parental strain. A statistical analysis of the data using a Wilcoxin Rank test indicated the differences in the numbers of <it>H. pylori </it>isolated from mice inoculated with the two strains were significant at the 99% confidence level. Levels of acetone associated with gastric tissue removed from uninfected mice were measured and found to range from 10–110 μmols per gram wet weight tissue.</p> <p>Conclusion</p> <p>The colonization defect of the <it>acxB:cat </it>mutant suggests a role for the <it>acxABC </it>operon in survival of the bacterium in the stomach. Products of the <it>H. pylori acxABC </it>operon may function primarily in acetone utilization or may catalyze a related reaction that is important for survival or growth in the host. <it>H. pylori </it>encounters significant levels of acetone in the stomach which it could use as a potential electron donor for microaerobic respiration.</p

Helicobacter pylori FlgR Is an Enhancer-Independent Activator of σ(54)-RNA Polymerase Holoenzyme

Helicobacter pylori FlgR activates transcription with σ(54)-RNA polymerase holoenzyme (σ(54)-holoenzyme) from at least five flagellar operons. Activators of σ(54)-holoenzyme generally bind enhancer sequences located >70 bp upstream of the promoter and contact σ(54)-holoenzyme bound at the promoter through DNA looping to activate transcription. H. pylori FlgR lacks the carboxy-terminal DNA-binding domain present in most σ(54)-dependent activators. As little as 42 bp of DNA upstream of the flaB promoter and 26 bp of DNA sequence downstream of the transcriptional start site were sufficient for efficient FlgR-mediated expression from a flaB′-′xylE reporter gene in H. pylori, indicating that FlgR does not use an enhancer to activate transcription. Other examples of σ(54)-dependent activators that lack a DNA-binding domain include Chlamydia trachomatis CtcC and activators from the other Chlamydia spp. whose genomes have been sequenced. FlgR from Helicobacter hepaticus and Campylobacter jejuni, which are closely related to H. pylori, appear to have carboxy-terminal DNA-binding domains, suggesting that the loss of the DNA-binding domain from H. pylori FlgR occurred after the divergence of these bacterial species. Removal of the amino-terminal regulatory domain of FlgR resulted in a constitutively active form of the protein that activated transcription from σ(54)-dependent genes in Escherichia coli. The truncated FlgR protein also activated transcription with E. coli σ(54)-holoenzyme in an in vitro transcription assay

Metabolomic Profiling and Mechanotransduction of Single Chondrocytes Encapsulated in Alginate Microgels

Articular cartilage is comprised of two main components, the extracellular matrix (ECM) and the pericellular matrix (PCM). The PCM helps to protect chondrocytes in the cartilage from mechanical loads, but in patients with osteoarthritis, the PCM is weakened, resulting in increased chondrocyte stress. As chondrocytes are responsible for matrix synthesis and maintenance, it is important to understand how mechanical loads affect the cellular responses of chondrocytes. Many studies have examined chondrocyte responses to in vitro mechanical loading by embedding chondrocytes in 3-D hydrogels. However, these experiments are mostly performed in the absence of PCM, which may obscure important responses to mechanotransduction. Here, drop-based microfluidics is used to culture single chondrocytes in alginate microgels for cell-directed PCM synthesis that closely mimics the in vivo microenvironment. Chondrocytes formed PCM over 10 days in these single-cell 3-D microenvironments. Mechanotransduction studies were performed, in which single-cell microgels mimicking the cartilage PCM were embedded in high-stiffness agarose. After physiological dynamic compression in a custom-built bioreactor, microgels exhibited distinct metabolomic profiles from both uncompressed and monolayer controls. These results demonstrate the potential of single cell encapsulation in alginate microgels to advance cartilage tissue engineering and basic chondrocyte mechanobiology

The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice-2

<p><b>Copyright information:</b></p><p>Taken from "The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice"</p><p>http://www.biomedcentral.com/1471-2180/8/14</p><p>BMC Microbiology 2008;8():14-14.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2244623.</p><p></p>unts. Each spot represents the cfu count from one mouse, expressed as the value of log(cfu/g stomach) in the Y-axis. The base line [log(cfu/g stomach) = 2.7] is the detection limit of the assay, which represents the count below 500 cfu/g stomach

The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice-1

<p><b>Copyright information:</b></p><p>Taken from "The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice"</p><p>http://www.biomedcentral.com/1471-2180/8/14</p><p>BMC Microbiology 2008;8():14-14.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2244623.</p><p></p>ding the enzymes responsible for catalyzing each reaction are indicated

The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice-0

<p><b>Copyright information:</b></p><p>Taken from "The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice"</p><p>http://www.biomedcentral.com/1471-2180/8/14</p><p>BMC Microbiology 2008;8():14-14.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2244623.</p><p></p>iven a gene designation in the annotated genome sequences are indicated with either an hp designation (for 26695), a jhp designation (for J99), or only the open reading frame number (for HPAG1 and strain Sheeba). Orthologous genes in the four strains are the same color. The genes jhp0628 in J99 and 0671 in HPAG1 correspond to a fusion of hp0688 and hp0689 from 26695. J99 and HPAG1 have two genes within this region, jhp0629 (HPAG1_0672) and jhp0630 (HPAG1_0672), that encode a type II DNA methyltransferase and a type II restriction enzyme, respectively, and are not found in 26695. Functions of the products of the genes within the acetone metabolism cluster are described in the text. The proposed functions of the products of the surrounding genes are: , iron(III) dicitrate transport protein; , iron(II) transport protein; , diacylglycerol kinase; , subunit A of DNA gyrase; , anaerobic C-dicarboxylate transporter; and , asparaginase II

The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice-5

<p><b>Copyright information:</b></p><p>Taken from "The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice"</p><p>http://www.biomedcentral.com/1471-2180/8/14</p><p>BMC Microbiology 2008;8():14-14.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2244623.</p><p></p>ding the enzymes responsible for catalyzing each reaction are indicated

The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice-3

<p><b>Copyright information:</b></p><p>Taken from "The human gastric pathogen has a potential acetone carboxylase that enhances its ability to colonize mice"</p><p>http://www.biomedcentral.com/1471-2180/8/14</p><p>BMC Microbiology 2008;8():14-14.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2244623.</p><p></p>ng their stomachs (post-mortem), and for four mice that were anesthetized after which their stomachs were removed (pre-mortem). Excised mouse stomachs were placed immediately in sealed vials that were then placed on ice for at least 30 min to allow acetone associated with the gastric tissue to equilibrate with the gas phase. Acetone levels in the gas phases of the vials were measured by gas chromatography and estimated from standard curves generated for each vial. Each value represents an average of at least three measurements and error bars indicate the standard deviations for each sample