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  • 1.
    Blanco-Rivero, A
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid 28049, Spain .
    Leganés, F
    Fernández-Valiente, E
    Calle, P
    Fernández-Piñas, F
    mrpA, a gene with roles in resistance to Na+ and adaptation to alkaline pH in the cyanobacterium Anabaena sp. PCC71202005In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 151, no Pt 5, p. 1671-1682Article in journal (Refereed)
    Abstract [en]

    Transposon mutagenesis of Anabaena sp. PCC7120 led to the isolation of a mutant strain, PHB11, which grew poorly at pH values above 10. The mutant strain exhibited pronounced Na+ sensitivity; this sensitivity was higher under basic conditions. Mutant PHB11 also showed an inhibition of photosynthesis that was much more pronounced at alkaline pH. Reconstruction of the transposon mutation of PHB11 in the wild-type strain reproduced the phenotype of the original mutant. The wild-type version of the mutated gene was cloned and the mutation complemented. In mutant strain PHB11, the transposon had inserted within an ORF that is part of a seven-ORF operon with significant sequence similarity to a family of bacterial operons that are believed to code for a novel multiprotein cation/proton antiporter primarily involved in resistance to salt stress and adaptation to alkaline pH. The Anabaena operon was denoted mrp (multiple resistance and pH adaptation) following the nomenclature of the Bacillus subtilis operon; the ORF mutated in PHB11 corresponded to mrpA. Computer analysis suggested that all seven predicted Anabaena Mrp proteins were highly hydrophobic with several transmembrane domains; in fact, the predicted protein sequences encoded by mrpA, mrpB and mrpC showed significant similarity to hydrophobic subunits of the proton pumping NADH : ubiquinone oxidoreductase. In vivo expression studies indicated that mrpA is induced with increasing external Na+ concentrations and alkaline pH; mrpA is also upregulated under inorganic carbon (Ci) limitation. The biological significance of a putative cyanobacterial Mrp complex is discussed.

  • 2.
    Bröms, Jeanette
    et al.
    Umeå University, Faculty of Medicine, Molecular Biology.
    Forslund, Anna-Lena
    Umeå University, Faculty of Science and Technology, Molecular Biology (Faculty of Science and Technology).
    Forsberg, Åke
    Umeå University, Faculty of Science and Technology, Molecular Biology (Faculty of Science and Technology).
    Francis, Matthew
    Umeå University, Faculty of Science and Technology, Molecular Biology (Faculty of Science and Technology).
    Dissection of homologous translocon operons reveals a distinct role for YopD in type III secretion by Yersinia pseudotuberculosis.2003In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Microbiology, Vol. 149, no 9, p. 2615-2626Article in journal (Refereed)
    Abstract [en]

    The homologous pcrGVHpopBD and lcrGVHyopBD translocase operons of Pseudomonas aeruginosa and pathogenic Yersinia spp., respectively, are responsible for the translocation of anti-host effectors into the cytosol of infected eukaryotic cells. In Yersinia, this operon is also required for yop-regulatory control. To probe for key molecular interactions during the infection process, the functional interchangeability of popB/yopB and popD/yopD was investigated. Secretion of PopB produced in trans in a yopB null mutant of Yersinia was only observed when co-produced with its native chaperone PcrH, but this was sufficient to complement the yopB translocation defect. The Yersinia yopD null mutant synthesized and secreted PopD even in the absence of native PcrH, yet this did not restore YopD-dependent yop-regulatory control or effector translocation. Thus, this suggests that key residues in YopD, which are not conserved in PopD, are essential for functional Yersinia type III secretion.

  • 3. Durand, Jérôme M B
    et al.
    Björk, Glenn R
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Metabolic control through ornithine and uracil of epithelial cell invasion by Shigella flexneri2009In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 155, no Pt 8, p. 2498-2508Article in journal (Refereed)
    Abstract [en]

    This paper shows that compounds in defined growth media strongly influence the expression of the effectors of virulence in the human invasive pathogen Shigella flexneri. Ornithine in conjunction with uracil reduces the haemolytic ability of wild-type cultures more than 20-fold and the expression of the type III secretion system more than 8-fold, as monitored by an mxiC : : lacZ transcriptional reporter. mxiC gene expression is further decreased by the presence of methionine or branched-chain amino acids (15-fold or 25-fold at least, respectively). Lysine and a few other aminated metabolites (cadaverine, homoserine and diaminopimelate) counteract the ornithine-mediated inhibition of haemolytic activity and of the expression of a transcriptional activator virF reporter. The complete abolition of invasion of HeLa cells by wild-type bacteria by ornithine, uracil, methionine or branched-chain amino acids establishes that these metabolites are powerful effectors of virulence. These findings provide a direct connection between metabolism and virulence in S. flexneri. The inhibitory potential exhibited by the nutritional environment is stronger than temperature, the classical environmental effector of virulence. The implications and practical application of this finding in prophylaxis and treatment of shigellosis are discussed.

  • 4.
    Garbom, Sara
    et al.
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Olofsson, Martina
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Björnfot, Ann-Catrin
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Srivastava, Manoj Kumar
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, S-90183 Umeå, Sweden.
    Robinson, Victoria L
    Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
    Oyston, Petra C F
    Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
    Titball, Richard W
    Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
    Wolf-Watz, Hans
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Phenotypic characterization of a virulence-associated protein, VagH, of Yersinia pseudotuberculosis reveals a tight link between VagH and the type III secretion system.2007In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 153, no Pt 5, p. 1464-73Article in journal (Refereed)
    Abstract [en]

    Recently, a number of attenuated mutants of Yersinia pseudotuberculosis have been identified using a bioinformatics approach. One of the target genes identified in that study was vagH, which the authors now characterized further. VagH shows homology to HemK of Escherichia coli, possessing methyltransferase activity similar to that of HemK, and targeting release factors 1 and 2. Microarray studies comparing the wild-type and the vagH mutant revealed that the mRNA levels of only a few genes were altered in the mutant. By proteome analysis, expression of the virulence determinant YopD was found to be increased, indicating a possible connection between VagH and the virulence plasmid-encoded type III secretion system (T3SS). Further analysis showed that Yop expression and secretion were repressed in a vagH mutant. This phenotype could be suppressed by trans-complementation with the wild-type vagH gene or by deletion of the negative regulator yopD. Also, in a similar manner to a T3SS-negative mutant, the avirulent vagH mutant was rapidly cleared from Peyer's patches and could not reach the spleen after oral infection of mice. In a manner analogous to that of T3SS mutants, the vagH mutant could not block phagocytosis by macrophages. However, a vagH mutant showed no defects in the T3SS-independent ability to proliferate intracellularly and replicated to levels similar to those of the wild-type in macrophages. In conclusion, the vagH mutant exhibits a virulence phenotype similar to that of a T3SS-negative mutant, indicating a tight link between VagH and type III secretion in Y. pseudotuberculosis.

  • 5.
    Jonsson, Maria
    et al.
    Umeå University, Faculty of Medicine, Microbiology.
    Bergström, Sven
    Umeå University, Faculty of Medicine, Microbiology.
    Transcriptional and translational regulation of the expression of the major outer surface proteins in Lyme disease Borrelia strains1995In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 141, no 6, p. 1321-1329Article in journal (Refereed)
    Abstract [en]

    The major outer surface proteins of Lyme disease spirochaetes are differentially expressed in different isolates. Borrelia afzelii strain F1 expresses none, or very low amounts, of the OspA and OspB proteins. To elucidate the mechanisms that control the expression of these abundant surface proteins the ospAB operon of B. afzelii F1 was cloned, sequenced and compared to the previously sequenced ospAB operon of B. afzelii ACAI and Borrelia burgdorferi B31. The two B. afzelii strains showed almost 100% identity at the DNA level, although Coomassie-stained gels and Western blot analyses showed significant variation in the Osp protein content. Transcriptional analysis revealed that the amount of ospAB mRNA produced in B. afzelii F1 varies more than the amount of protein, suggesting that the expression of OspA and OspB proteins is regulated at both the transcriptional and the translational level. Furthermore, the inverse relationship between the transcription of ospC and the ospAB operon could indicate coregulation of these separately encoded operons.

  • 6. O'Toole, R
    et al.
    Milton, Debra L
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Hörstedt, P
    Wolf-Watz, H
    RpoN of the fish pathogen Vibrio (Listonella) anguillarum is essential for flagellum production and virulence by the water-borne but not intraperitoneal route of inoculation.1997In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 143 ( Pt 12)Article in journal (Refereed)
    Abstract [en]

    To investigate the involvement of RpoN in flagellum production and pathogenicity of Vibrio (Listonella) anguillarum, the rpoN gene was cloned and sequenced. The deduced product of the rpoN gene displayed strong homology to the alternative sigma 54 factor (RpoN) of numerous species of bacteria. In addition, partial sequencing of rpoN-linked ORFs revealed a marked resemblance to similarly located ORFs in other bacterial species. A polar insertion or an in-frame deletion in the coding region of rpoN abolished expression of the flagellin subunits and resulted in loss of motility. Introduction of the rpoN gene of V. anguillarum or Pseudomonas putida into the rpoN mutants restored flagellation and motility. The rpoN mutants were proficient in the expression of other proposed virulence determinants of V. anguillarum, such as ability to grow under low available iron conditions, and expression of the LPS O-antigen and of haemolytic and proteolytic extracellular products. The infectivity of the rpoN mutants with respect to the wild-type strain was unaffected following intraperitoneal injection of fish but was reduced significantly when fish were immersed in bacteria-containing water. Thus, RpoN does not appear to regulate any factors required for virulence subsequent to penetration of the fish epithelium, but is important in the infection of fish by water-borne V. anguillarum.

  • 7.
    Pinne, Marija
    et al.
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Östberg, Yngve
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Comstedt, Pär
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Bergström, Sven
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Molecular analysis of the channel-forming protein P13 and its paralogue family 48 from different Lyme disease Borrelia species2004In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 150, no Pt 3, p. 549-559Article in journal (Refereed)
    Abstract [en]

    The aetiological agent of Lyme disease, Borrelia burgdorferi cycles between its tick vector and mammalian hosts, implying that it can sense different environments and consequently change the expression of genes encoding several surface-associated proteins. The genome of the type strain B. burgdorferi B31 has revealed 175 different gene families. The p13 gene, situated on the chromosome, encodes a channel-forming protein that belongs to the gene family 48 consisting of eight additional paralogous genes. The heterogeneity of the P13 protein from different Lyme disease Borrelia strains was investigated. The predicted surface-exposed domains are the most heterogeneous regions and contain probable epitopes of P13. The membrane-spanning architecture of P13 was determined and a model for the location of this protein in the outer membrane is presented. The transcription of the paralogues of gene family 48 during in vitro culturing and in a mouse infection model was also analysed. The bba01 gene is the only p13 paralogue present in all three Lyme-disease-causing genospecies; it is stable during cultivation in vitro and the BBA01 protein was expressed in all Borrelia strains investigated. Conversely, paralogues bbi31, bbq06 and bbh41 were only detected in B. burgdorferi and the corresponding plasmids harbouring bbi31 and bbh41 were lost during in vitro passage. Finally, p13 and bbi31 are the only members of gene family 48 that are transcribed in mice, suggesting their importance during mammalian infection.

  • 8. Platt, A
    et al.
    Shingler, V
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Taylor, S C
    Williams, P A
    The 4-hydroxy-2-oxovalerate aldolase and acetaldehyde dehydrogenase (acylating) encoded by the nahM and nahO genes of the naphthalene catabolic plasmid pWW60-22 provide further evidence of conservation of meta-cleavage pathway gene sequences.1995In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 141 ( Pt 9)Article in journal (Refereed)
    Abstract [en]

    We report the complete nucleotide sequence and over-expression of the nahOM genes for the acetaldehyde dehydrogenase (acylating) and the 4-hydroxy-2-oxovalerate aldolase from the meta pathway operon of the naphthalene catabolic plasmid pWW60-22 from Pseudomonas sp. NCIMB9816. Additional partial sequence analysis of adjacent DNA shows the gene order within the operon to be nahNLOMK, identical to the order found for the isofunctional genes in the meta pathway operons in the toluene/xylene pathway of TOL plasmid pWW0 and the phenol/methylphenol pathway of pVI150. The deduced amino acid sequences of NahO and NahM were significantly homologous to the equivalent enzymes encoded by other Pseudomonas meta pathways, although both were the most divergent in each comparison. The nahOM genes were inserted downstream of the T7 promoter in the expression vector pET3a and similar constructs were also made of the isofunctional regions from pVI150 (dmpFG) and TOL plasmid pDK1 (xyIQK). High expression of all three gene pairs was detected by enzyme assays and by SDS-PAGE.

  • 9.
    Salomonsson, Emelie
    et al.
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). CBRN Defence and Security, FOI Swedish Defence Research Agency, Cementvägen 20, 901 82 Umeå, Sweden.
    Forsberg, Åke
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). CBRN Defence and Security, FOI Swedish Defence Research Agency, Cementvägen 20, 901 82 Umeå, Sweden.
    Roos, Norbert
    Holz, Claudia
    Maier, Berenike
    Koomey, Michael
    Winther-Larsen, Hanne C
    Functional analyses of pilin-like proteins from Francisella tularensis: complementation of type IV pilus phenotypes in Neisseria gonorrhoeae2009In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 155, p. 2546-2559Article in journal (Refereed)
    Abstract [en]

    Accumulating evidence from a number of studies strongly suggests that proteins orthologous to those involved in type IV pili (Tfp) assembly and function are required for Francisella pathogenicity. However, the molecular mechanisms by which the components exert their influence on virulence remain poorly understood. Owing to the conservation and promiscuity of Tfp biogenesis machineries, expression of Tfp pilins in heterologous species has been used successfully to analyse organelle structure-function relationships. In this study we expressed a number of Francisella pilin genes in the Tfp-expressing pathogen Neisseria gonorrhoeae lacking its endogenous pilin subunit. Two gene products, the orthologous PiIA proteins from Francisella tularensis subspecies tularensis and novicida, were capable of restoring the expression of Tfp-like appendages that were shown to be dependent upon the neisserial Tfp biogenesis machinery for surface localization. Expression of Francisella PiIA pilins also partially restored competence for natural transformation in N. gonorrhoeae. This phenotype was not complemented by expression of the PuIG and XcpT proteins, which are equivalent components of the related type II protein secretion system. Taken together, these findings provide compelling, although indirect, evidence of the potential for Francisella PiIA proteins to express functional Tfp.

  • 10.
    Wang, Su-Yan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Lauritz, Johan
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Jass, Jana
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Milton, Debra L
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Role for the major outer-membrane protein from Vibrio anguillarum in bile resistance and biofilm formation.2003In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 149, no Pt 4, p. 1061-1071Article in journal (Refereed)
    Abstract [en]

    Vibrio anguillarum, a fish pathogen, produces a 38 kDa major outer-membrane porin, which may be involved in environmental adaptation. The gene encoding the 38 kDa porin was cloned and deleted. The deduced protein sequence was 75 % identical to that of the major outer-membrane protein (OMP), OmpU, from Vibrio cholerae. LacZ expression from an ompU : : lacZ transcriptional gene fusion was increased 1.5-fold in the presence of bile salts and was decreased 50- to 100-fold in a toxR mutant compared to that in the wild-type, showing that ompU expression is positively regulated by ToxR and induced by bile salts. Similar to a toxR mutant, an ompU mutant showed a slight decrease in motility, an increased sensitivity to bile salts and a thicker biofilm with better surface area coverage compared to that of the wild-type. When ompU was expressed under a ToxR-independent promoter in the toxR mutant, the phenotypes for bile resistance and biofilm formation, but not motility were complemented to that of the wild-type. In rainbow trout, the ompU mutant showed wild-type virulence via immersion into infected seawater and intraperitoneal injection. The ompU mutant produced two colony morphologies: opaque, which did not grow at 0.2 % bile, and translucent, which grew at 2 % bile. The translucent ompU mutant strain produced a second major OMP that was induced by bile. All ompU mutants showed variations in the amount and length of smooth LPS. In V. anguillarum, OmpU is not required for virulence, possibly due to a second OMP also critical for resistance to bile; however, outside of the fish host, OmpU limits the progression of biofilm formation.

  • 11. Wasserström, Sebastian
    et al.
    Grantcharova, Nina
    Ubhayasekera, Wimal
    Ausmees, Nora
    Sandblad, Linda
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Flardh, Klas
    Non-sporulating ftsZ mutants in Streptomyces coelicolor reveal amino acid residues critical for FtsZ polymerization dynamics2013In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 159, p. 890-901Article in journal (Refereed)
    Abstract [en]

    During sporulation of Streptomyces coelicolor, the cytokinetic protein FtsZ is assembled into dozens of regularly spaced Z rings, which orchestrate the division of aerial hyphae into spores. We have previously found that a missense allele of ftsZ, ftsZ17(Spo), primarily affects sporulation septation rather than formation of cross-walls in vegetative mycelium. To clarify what aspect of FtsZ function is compromised in such non-sporulating mutants, we here use a genetic strategy to identify new ftsZ(Spo) alleles and describe how some of the mutations affect the biochemical properties of FtsZ. We have established a system for purification of recombinant untagged S. coelicolor FtsZ, and shown that it assembles dynamically into single protofilaments, displays a critical concentration indicative of cooperative assembly and has a rate of GTP hydrolysis that is substantially higher than that of the closely related Mycobacterium tuberculosis FtsZ. Of the nine isolated ftsZ(Spo) mutations, four affect the interface between the two main subdomains of FtsZ that is implicated in the assembly-induced conformational changes thought to mediate the GTP/GDP-driven cooperative assembly of FtsZ. We find that all these four mutations affect the polymerization behaviour of FtsZ in vitro. In addition, at least one ftsZ(Spo) mutation at the longitudinal contact surface between subunits in protofilaments strongly affects formation of polymers in vitro. We conclude that the assembly of Z rings during sporulation of S. coelicolor is highly sensitive to disturbances of FtsZ polymerization and therefore constitutes an excellent system for analysis of the elusive properties of FtsZ that mediate its characteristic polymerization dynamics.

  • 12.
    Weber, Barbara
    et al.
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Croxatto, Antony
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Chen, Chang
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Milton, Debra L
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    RpoS induces expression of the Vibrio anguillarum quorum-sensing regulator VanT2008In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 154, no 3, p. 767-780Article in journal (Refereed)
    Abstract [en]

    In vibrios, regulation of the Vibrio harveyi-like LuxR transcriptional activators occurs post-transcriptionally via small regulatory RNAs (sRNAs) that destabilize the luxR mRNA at a low cell population, eliminating expression of LuxR. Expression of the sRNAs is modulated by the vibrio quorum-sensing phosphorelay systems. However, vanT mRNA, which encodes a LuxR homologue in Vibrio anguillarum, is abundant at low and high cell density, indicating that VanT expression may be regulated via additional mechanisms. In this study, Western analyses showed that VanT was expressed throughout growth with a peak of expression during late exponential growth. VanO induced partial destabilization of vanT mRNA via activation of at least one Qrr sRNA. Interestingly, the sigma factor RpoS significantly stabilized vanT mRNA and induced VanT expression during late exponential growth. This induction was in part due to RpoS repressing expression of Hfq, an RNA chaperone. RpoS is not part of the quorum-sensing regulatory cascade since RpoS did not regulate expression or activity of VanO, and RpoS was not regulated by VanO or VanT. VanT and RpoS were needed for survival following UV irradiation and for pigment and metalloprotease production, suggesting that RpoS works with the quorum-sensing systems to modulate expression of VanT, which regulates survival and stress responses.

  • 13.
    Weber, Barbara
    et al.
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Lindell, Kristoffer
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    El Qaidi, Samir
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Hjerde, Erik
    Department of Chemistry, Faculty of Science and Technology, University of Tromsø, Tromsø 9037, Norway.
    Willassen, Nils-Peder
    Department of Chemistry, Faculty of Science and Technology, University of Tromsø, Tromsø 9037, Norway.
    Milton, Debra L
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    The phosphotransferase VanU represses expression of four qrr genes antagonizing VanO-mediated quorum-sensing regulation in Vibrio anguillarum2011In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 157, no 12, p. 3324-3339Article in journal (Refereed)
    Abstract [en]

    Vibrio anguillarum utilizes quorum sensing to regulate stress responses required for survival in the aquatic environment. Like other Vibrio species, V. anguillarum contains the gene qui, which encodes the ancestral quorum regulatory RNA Owl, and phosphorelay quorum-sensing systems that modulate the expression of small regulatory RNAs (sRNAs) that destabilize mRNA encoding the transcriptional regulator VanT. In this study, three additional Orr sRNAs were identified. All four sRNAs were positively regulated by sigma(54) and the sigma(54)-dependent response regulator Van, and showed a redundant activity. The Orr sRNAs, together with the RNA chaperone Hfq, destabilized vanT mRNA and modulated expression of VanT-regulated genes. Unexpectedly, expression of all four qrr genes peaked at high cell density, and exogenously added N-acylhomoserine lactone molecules induced expression of the qrr genes at low cell density. The phosphotransferase VanU, which phosphorylates and activates VanO, repressed expression of the Orr sRNAs and stabilized van T mRNA. A model is presented proposing that VanU acts as a branch point, aiding cross-regulation between two independent phosphorelay systems that activate or repress expression of the Orr sRNAs, giving flexibility and precision in modulating VanT expression and inducing a quorum-sensing response to stresses found in a constantly changing aquatic environment.

  • 14.
    Wiklund, Krister
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Hanqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stangner, Tim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Bullitt, Esther
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A drag force interpolation model for capsule-shaped cells in fluid flows near a surface2018In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 164, no 4, p. 483-494Article in journal (Refereed)
    Abstract [en]

    We report an interpolation model to calculate the hydrodynamic force on tethered capsule-shaped cells in micro-fluidic flows near a surface. Our model is based on numerical solutions of the full Navier–Stokes equations for capsule-shaped objects considering their geometry, aspect ratio and orientation with respect to fluid flow. The model reproduced the results from computational fluid dynamic simulations, with an average error of <0.15 % for objects with an aspect ratio up to 5, and the model exactly reproduced the Goldman approximation of spherical objects close to a surface. We estimated the hydrodynamic force imposed on tethered Escherichia coli cells using the interpolation model and approximate models found in the literature, for example, one that assumes that E. coli is ellipsoid shaped. We fitted the 2D-projected area of a capsule and ellipsoid to segmented E. coli cells. We found that even though an ellipsoidal shape is a reasonable approximation of the cell shape, the capsule gives 4.4 % better agreement, a small difference that corresponds to 15 % difference in hydrodynamic force. In addition, we showed that the new interpolation model provides a significantly better agreement compared to estimates from commonly used models and that it can be used as a fast and accurate substitute for complex and computationally heavy fluid dynamic simulations. This is useful when performing bacterial adhesion experiments in parallel-plate flow channels. We include a MATLAB script that can track cells in a video time-series and estimate the hydrodynamic force using our interpolation formula.

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