scholarly journals Megaplasmid pRme2011a of Sinorhizobium meliloti Is Not Required for Viability

2000 ◽  
Vol 182 (12) ◽  
pp. 3582-3586 ◽  
Author(s):  
Ivan J. Oresnik ◽  
Shu-Lin Liu ◽  
Christopher K. Yost ◽  
Michael F. Hynes
Keyword(s):  
Gel Electrophoresis ◽  
Type Strain ◽  
Sinorhizobium Meliloti ◽  
Wild Type Strain ◽  
Sole Source ◽  
Pulsed Field Gel Electrophoresis ◽  
Selection Strategy ◽  
Wild Type ◽  
Defined Media

ABSTRACT We report the curing of the 1,360-kb megaplasmid pRme2011a fromSinorhizobium meliloti strain Rm2011. With a positive selection strategy that utilized Tn5B12-S containing thesacB gene, we were able to cure this replicon by successive rounds of selecting for deletion formation in vivo. Subsequent Southern blot, Eckhardt gel, and pulsed-field gel electrophoresis analyses were consistent with the hypothesis that the resultant strain was indeed missing pRme2011a. The cured derivative grew as well as the wild-type strain in both complex and defined media but was unable to use a number of substrates as a sole source of carbon on defined media.

Identification of pilin pools in the membranes of Pseudomonas aeruginosa

1982 ◽  
Vol 152 (2) ◽  
pp. 687-691
Author(s):  
T H Watts ◽  
E A Worobec ◽  
W Paranchych
Keyword(s):  
Staphylococcus Aureus ◽  
Pseudomonas Aeruginosa ◽  
Gel Electrophoresis ◽  
Type Strain ◽  
Wild Type Strain ◽  
Polyacrylamide Gel Electrophoresis ◽  
Protein A ◽  
Sodium Dodecyl ◽  
Wild Type ◽  
Outer Membranes

The proteins of purified inner and outer membranes obtained from Pseudomonas aeruginosa strains PAK and PAK/2Pfs were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and treated with antiserum raised against pure pili. Bound antipilus antibodies were visualized by reaction with 125I-labeled protein A from Staphylococcus aureus. The results showed that there are pools of pilin in both the inner and outer membranes of P. aeruginosa and that the pool size in the multipiliated strain is comparable with that of the wild-type strain.

scholarly journals In VivoEfficacy of Human Simulated Regimens of Carbapenems and Comparator Agents against NDM-1-Producing Enterobacteriaceae

2013 ◽  
Vol 58 (3) ◽  
pp. 1671-1677 ◽  
Author(s):  
Dora E. Wiskirchen ◽  
Patrice Nordmann ◽  
Jared L. Crandon ◽  
David P. Nicolau
Keyword(s):  
Type Strain ◽  
Wild Type Strain ◽  
Similar Efficacy ◽  
Infection Model ◽  
High Dose ◽  
Wild Type ◽  
Prolonged Infusion ◽  
Content Type

ABSTRACTDoripenem and ertapenem have demonstrated efficacy against several NDM-1-producing isolatesin vivo, despite having high MICs. In this study, we sought to further characterize the efficacy profiles of humanized regimens of standard (500 mg given every 8 h) and high-dose, prolonged infusion of doripenem (2 g given every 8 h, 4-h infusion) and 1 g of ertapenem given intravenously every 24 h and the comparator regimens of ceftazidime at 2 g given every 8 h (2-h infusion), levofloxacin at 500 mg every 24 h, and aztreonam at 2 g every 6 h (1-h infusion) against a wider range of isolates in a murine thigh infection model. An isogenic wild-type strain and NDM-1-producingKlebsiella pneumoniaeand eight clinical NDM-1-producing members of the familyEnterobacteriaceaewere tested in immunocompetent- and neutropenic-mouse models. The wild-type strain was susceptible to all of the agents, while the isogenic NDM-1-producing strain was resistant to ceftazidime, doripenem, and ertapenem. Clinical NDM-1-producing strains were resistant to nearly all five of the agents (two were susceptible to levofloxacin). In immunocompetent mice, all of the agents produced ≥1-log10CFU reductions of the isogenic wild-type and NDM-1-producing strains after 24 h. Minimal efficacy of ceftazidime, aztreonam, and levofloxacin against the clinical NDM-1-producing strains was observed. However, despitein vitroresistance, ≥1-log10CFU reductions of six of eight clinical strains were achieved with high-dose, prolonged infusion of doripenem and ertapenem. Slight enhancements of doripenem activity over the standard doses were obtained with high-dose, prolonged infusion for three of the four isolates tested. Similar efficacy observations were noted in neutropenic mice. These data suggest that carbapenems are a viable treatment option for infections caused by NDM-1-producingEnterobacteriaceae.

scholarly journals Analysis and Manipulation of Aspartate Pathway Genes for l-Lysine Overproduction from Methanol by Bacillus methanolicus

2011 ◽  
Vol 77 (17) ◽  
pp. 6020-6026 ◽  
Author(s):  
Ingemar Nærdal ◽  
Roman Netzer ◽  
Trond E. Ellingsen ◽  
Trygve Brautaset
Keyword(s):  
Type Strain ◽  
Wild Type Strain ◽  
Feedback Inhibition ◽  
Wild Type ◽  
Content Type ◽  
Bacillus Methanolicus ◽  
Semialdehyde Dehydrogenase ◽  
Aspartate Pathway ◽  
Lysine Overproduction

ABSTRACTWe investigated the regulation and roles of six aspartate pathway genes inl-lysine overproduction inBacillus methanolicus:dapG, encoding aspartokinase I (AKI);lysC, encoding AKII;yclM, encoding AKIII;asd, encoding aspartate semialdehyde dehydrogenase;dapA, encoding dihydrodipicolinate synthase; andlysA, encodingmeso-diaminopimelate decarboxylase. Analysis of the wild-type strain revealed thatin vivo lysCtranscription was repressed 5-fold byl-lysine and induced 2-fold bydl-methionine added to the growth medium. Surprisingly,yclMtranscription was repressed 5-fold bydl-methionine, while thedapG,asd,dapA, andlysAgenes were not significantly repressed by any of the aspartate pathway amino acids. We show that thel-lysine-overproducing classicalB. methanolicusmutant NOA2#13A52-8A66 has—in addition to ahom-1mutation—chromosomal mutations in thedapGcoding region and in thelysApromoter region. No mutations were found in itsdapA,lysC,asd, andyclMgenes. The mutantdapGgene product had abolished feedback inhibition bymeso-diaminopimelatein vitro, and thelysAmutation was accompanied by an elevated (6-fold)lysAtranscription levelin vivo. Moreover,yclMtranscription was increased 16-fold in mutant strain NOA2#13A52-8A66 compared to the wild-type strain. Overexpression of wild-type and mutant aspartate pathway genes demonstrated that all six genes are important forl-lysine overproduction as tested in shake flasks, and the effects were dependent on the genetic background tested. Coupled overexpression of up to three genes resulted in additive (above 80-fold) increasedl-lysine production levels.

scholarly journals Contribution of Urease to Colonization by Shiga Toxin-Producing Escherichia coli

2012 ◽  
Vol 80 (8) ◽  
pp. 2589-2600 ◽  
Author(s):  
Susan R. Steyert ◽  
James B. Kaper
Keyword(s):  
Escherichia Coli ◽  
Shiga Toxin ◽  
Type Strain ◽  
Nitrogen Availability ◽  
Wild Type Strain ◽  
Clinical Manifestations ◽  
Maximum Activity ◽  
Wild Type ◽  
Urease Enzyme

ABSTRACTShiga toxin-producingEscherichia coli(STEC) is a food-borne pathogen with a low infectious dose that colonizes the colon in humans and can cause severe clinical manifestations such as hemolytic-uremic syndrome. The urease enzyme, encoded in the STEC chromosome, has been demonstrated to act as a virulence factor in other bacterial pathogens. The NH3produced as urease hydrolyzes urea can aid in buffering bacteria in acidic environments as well as provide an easily assimilated source of nitrogen that bacteria can use to gain a metabolic advantage over intact microflora. Here, we explore the role of urease in STEC pathogenicity. The STEC urease enzyme exhibited maximum activity near neutral pH and during the stationary-growth phase. Experiments altering growth conditions performed with three phylogenetically distinct urease-positive strains demonstrated that the STECuregene cluster is inducible by neither urea nor pH but does respond to nitrogen availability. Quantitative reverse transcription-PCR (qRT-PCR) data indicate that nitrogen inhibits the transcriptional response. The deletion of theuregene locus was constructed in STEC strain 88-0643, and theuremutant was used with the wild-type strain in competition experiments in mouse models to examine the contribution of urease. The wild-type strain was twice as likely to survive passage through the acidic stomach and demonstrated an enhanced ability to colonize the intestinal tract compared to theuremutant strain. Thesein vivoexperiments reveal that, although the benefit STEC gains from urease expression is modest and not absolutely required for colonization, urease can contribute to the pathogenicity of STEC.

scholarly journals Regulation of ppk Expression and In Vivo Function of Ppk in Streptomyces lividans TK24

2006 ◽  
Vol 188 (17) ◽  
pp. 6269-6276 ◽  
Author(s):  
Sofiane Ghorbel ◽  
Aleksey Smirnov ◽  
Hichem Chouayekh ◽  
Brice Sperandio ◽  
Catherine Esnault ◽  
...  
Keyword(s):  
Mutant Strain ◽  
Type Strain ◽  
Wild Type Strain ◽  
Sufficient Conditions ◽  
Streptomyces Lividans ◽  
Antibiotic Biosynthesis ◽  
Wild Type ◽  
In The Wild

ABSTRACT The ppk gene of Streptomyces lividans encodes an enzyme catalyzing, in vitro, the reversible polymerization of the γ phosphate of ATP into polyphosphate and was previously shown to play a negative role in the control of antibiotic biosynthesis (H. Chouayekh and M. J. Virolle, Mol. Microbiol. 43:919-930, 2002). In the present work, some regulatory features of the expression of ppk were established and the polyphosphate content of S. lividans TK24 and the ppk mutant was determined. In Pi sufficiency, the expression of ppk was shown to be low but detectable. DNA gel shift experiments suggested that ppk expression might be controlled by a repressor using ATP as a corepressor. Under these conditions, short acid-soluble polyphosphates accumulated upon entry into the stationary phase in the wild-type strain but not in the ppk mutant strain. The expression of ppk under Pi-limiting conditions was shown to be much higher than that under Pi-sufficient conditions and was under positive control of the two-component system PhoR/PhoP. Under these conditions, the polyphosphate content of the cell was low and polyphosphates were reproducibly found to be longer and more abundant in the ppk mutant strain than in the wild-type strain, suggesting that Ppk might act as a nucleoside diphosphate kinase. In light of our results, a novel view of the role of this enzyme in the regulation of antibiotic biosynthesis in S. lividans TK24 is proposed.

scholarly journals A Single Amino Acid at Residue 188 of Hexon Protein is Responsible for the Pathogenicity of the Emerging Novel Fowl Adenovirus 4

2021 ◽  
Author(s):  
Yu Zhang ◽  
Aijing Liu ◽  
Yanan Wang ◽  
Hongyu Cui ◽  
Yulong Gao ◽  
...  
Keyword(s):  
Amino Acid ◽  
Mutant Strain ◽  
Molecular Basis ◽  
Type Strain ◽  
Wild Type Strain ◽  
Wild Type ◽  
Live Attenuated Vaccine ◽  
Hexon Protein

Since 2015, severe hydropericardium-hepatitis syndrome (HHS) associated with a novel fowl adenovirus 4 (FAdV-4) has emerged in China, representing a new challenge for the poultry industry. Although various highly pathogenic FAdV-4 strains have been isolated, the virulence factor and the pathogenesis of novel FAdV-4 are unclear. In our previous studies, we reported that a large genomic deletion (1966 bp) is not related to increased virulence. In this study, two recombinant chimeric viruses, rHN20 strain and rFB2 strain, were generated from a highly pathogenic FAdV-4 strain by replacing hexon or fiber-2 gene of a non-pathogenic FAdV-4, respectively. Both chimeric strains showed similar titers to the wild type strain in vitro . Notably, rFB2 and the wild type strain induced 100% mortality, while no mortality or clinical signs appeared in chickens inoculated with rHN20, indicating that hexon, but not fiber-2, determines the novel FAdV-4 virulence. Furthermore, an R188I mutation in the hexon protein identified residue 188 as the key amino acid for the reduced pathogenicity. The rR188I mutant strain was significantly neutralized by chicken serum in vitro and in vivo , whereas the wild type strain was able to replicate efficiently. Finally, the immunogenicity of the rescued rR188I was investigated. Non-pathogenic rR188I provided full protection against lethal FAdV-4 challenge. Collectively, these findings provide an in-depth understanding of the molecular basis of novel FAdV-4 pathogenicity and present rR188I as a potential live attenuated vaccine candidate or a novel vaccine vector for HHS vaccines. Importance HHS associated with a novel FAdV-4 infection in chickens has caused huge economic losses to the poultry industry in China since 2015. The molecular basis for the increased virulence remains largely unknown. Here, we demonstrate that the hexon gene is vital for FAdV-4 pathogenicity. Furthermore, we show that the amino acid residue at position 188 of the hexon protein is responsible for pathogenicity. Importantly, the rR188I mutant strain was neutralized by chicken serum in vitro and in vivo , whereas the wild type strain was not. Further, the rR188I mutant strain provided complete protection against FAdV-4 challenge. Our results provide a molecular basis of the increased virulence of novel FAdV-4. We propose that the rR188I mutant is a potential live attenuated vaccine against HHS and a new vaccine vector for HHS-combined vaccines.

A Stable 44S Intermediate in the Autodigestion of 50S Ribosomal Subunits

1971 ◽  
Vol 29 ◽  
pp. 430-431
Author(s):  
John H. Nisbet ◽  
Henry S. Slayter
Keyword(s):  
Escherichia Coli ◽  
Molecular Weight ◽  
Ribosomal Rna ◽  
Gel Electrophoresis ◽  
Type Strain ◽  
Wild Type Strain ◽  
Ribosomal Subunit ◽  
Wild Type ◽  
Ribosomal Subunits ◽  
Type Strains

Wild - type strains of Escherichia coli are known to contain as many as four endogenous nucleases (Ref. 1). These are commonly found associated with the ribosomes after extraction from the cell, but may be removed, with the exception of RNase IV, by washing the ribosomes in NH4Cl (at 0.2 M and higher concentrations). We have examined the effect of these nucleases on the 50S ribosomal subunit of one wild-type strain, K12 (Hfr 3000), by incubating the unwashed particles at 37° in the presence of varying magnesium concentrations.At 10-4 molar magnesium (slower at 10-3 molar), the 50S particle is converted to a species sedimenting at about 44S. About 20% of the total O.D260 is liberated at the same time. Continued incubation leads to the release of more O.D260 material while the RNA remaining in the 44S (Fig. 1) particle is progressively cleaved, eventually to the point where it consists of one principal fragment of molecular weight 0.42 x 106 daltons and several lesser fragments. The ribosomal RNA and proteins have been characterized by acrylamide gel electrophoresis.

scholarly journals Improvement of Phosphate Solubilization and Medicago Plant Yield by an Indole-3-Acetic Acid-Overproducing Strain of Sinorhizobium meliloti

2010 ◽  
Vol 76 (14) ◽  
pp. 4626-4632 ◽  
Author(s):  
Carmen Bianco ◽  
Roberto Defez
Keyword(s):  
Acetic Acid ◽  
Plant Growth ◽  
Type Strain ◽  
Sinorhizobium Meliloti ◽  
Wild Type Strain ◽  
Dry Weight ◽  
Limiting Factors ◽  
Wild Type ◽  
System A ◽  
Indole 3 Acetic Acid

ABSTRACT Nitrogen (N) and phosphorus (P) are the most limiting factors for plant growth. Some microorganisms improve the uptake and availability of N and P, minimizing chemical fertilizer dependence. It has been published that the RD64 strain, a Sinorhizobium meliloti 1021 strain engineered to overproduce indole-3-acetic acid (IAA), showed improved nitrogen fixation ability compared to the wild-type 1021 strain. Here, we present data showing that RD64 is also highly effective in mobilizing P from insoluble sources, such as phosphate rock (PR). Under P-limiting conditions, the higher level of P-mobilizing activity of RD64 than of the 1021 wild-type strain is connected with the upregulation of genes coding for the high-affinity P transport system, the induction of acid phosphatase activity, and the increased secretion into the growth medium of malic, succinic, and fumaric acids. Medicago truncatula plants nodulated by RD64 (Mt-RD64), when grown under P-deficient conditions, released larger amounts of another P-solubilizing organic acid, 2-hydroxyglutaric acid, than plants nodulated by the wild-type strain (Mt-1021). It has already been shown that Mt-RD64 plants exhibited higher levels of dry-weight production than Mt-1021 plants. Here, we also report that P-starved Mt-RD64 plants show significant increases in both shoot and root fresh weights when compared to P-starved Mt-1021 plants. We discuss how, in a Rhizobium-legume model system, a balanced interplay of different factors linked to bacterial IAA overproduction rather than IAA production per se stimulates plant growth under stressful environmental conditions and, in particular, under P starvation.

scholarly journals Environmental Regulation of Exopolysaccharide Production in Sinorhizobium meliloti

2000 ◽  
Vol 182 (3) ◽  
pp. 599-606 ◽  
Author(s):  
Kiprian E. Mendrygal ◽  
Juan E. González
Keyword(s):  
Molecular Weight ◽  
Type Strain ◽  
Sinorhizobium Meliloti ◽  
Wild Type Strain ◽  
Root Nodules ◽  
Weight Fraction ◽  
Wild Type ◽  
Exopolysaccharide Production ◽  
Successful Establishment ◽  
High Phosphate

ABSTRACT Exopolysaccharide production by Sinorhizobium melilotiis required for invasion of root nodules on alfalfa and successful establishment of a nitrogen-fixing symbiosis between the two partners.S. meliloti wild-type strain Rm1021 requires production of either succinoglycan, a polymer of repeating octasaccharide subunits, or EPS II, an exopolysaccharide of repeating dimer subunits. The reason for the production of two functional exopolysaccharides is not clear. Earlier reports suggested that low-phosphate conditions stimulate the production of EPS II in Rm1021. We found that phosphate concentrations determine which exopolysaccharide is produced by S. meliloti. The low-phosphate conditions normally found in the soil (1 to 10 μM) stimulate EPS II production, while the high-phosphate conditions inside the nodule (20 to 100 mM) block EPS II synthesis and induce the production of succinoglycan. Interestingly, the EPS II produced by S. meliloti in low-phosphate conditions does not allow the invasion of alfalfa nodules. We propose that this invasion phenotype is due to the lack of the active molecular weight fraction of EPS II required for nodule invasion. An analysis of the function of PhoB in this differential exopolysaccharide production is presented.

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