Characterization of Bacteroides fragilis Hemolysins and Regulation and Synergistic Interactions of HlyA and HlyB

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dc.contributor.authorRobertson, Kirstin P.en_US
dc.contributor.authorSmith, C. Jeffreyen_US
dc.contributor.authorGough, Andrea M.en_US
dc.contributor.authorRocha, Edson R.en_US
dc.date.accessioned2011-04-28T15:35:38Zen_US
dc.date.accessioned2011-05-17T01:40:11Z
dc.date.available2011-04-28T15:35:38Zen_US
dc.date.available2011-05-17T01:40:11Z
dc.date.issued2006-04en_US
dc.description.abstractThis study describes the presence of 10 hemolysin orthologs in the genome of the opportunistic human anaerobic pathogen Bacteroides fragilis, which is currently classified as a nonhemolytic bacterium. The hemolysins were designated HlyA through HlyI plus HlyIII. All cloned hemolysin genes were able to confer hemolytic activity to a nonhemolytic Escherichia coli strain on blood agar plates. Interestingly, HlyH was found to be present in the genome of the B. fragilis NCTC9343 strain but absent in strains 638R, YCH46, and Bacteroides thetaiotaomicron VPI-5482. The hemolysins HlyA, HlyB, and HlyIII were selected for further characterization. HlyA, HlyB, and HlyIII were cytolytic to erythrocytes on liquid hemolytic assay. When hlyA and hlyB were expressed together in a nonhemolytic E. coli strain, the strain showed enhanced hemolytic activity on blood agar plates. Further analysis revealed that HlyA and HlyB have synergistic hemolytic activity as detected by the liquid hemolytic assay. In addition, the two-component hemolysins HlyA and HlyB form a protein-protein complex in vivo as determined by bacterial two-hybrid system assay. The hlyB and hlyA genes are organized in an operon that is coordinately regulated by iron and oxygen. Northern blot hybridization analysis revealed that hlyBA were expressed as a bicistronic mRNA induced approximately 2.5-fold under low-iron conditions and repressed in iron-rich medium. The normal ironregulated expression of hlyBA mRNA was lost in the furA mutant strain. In contrast, the hlyA gene was also expressed as a single mRNA in iron-rich medium, but its expression was reduced approximately threefold under low-iron conditions in a Fur-independent manner. This suggests that hlyA alone is regulated by an unidentified iron-dependent regulator. Moreover, the expression levels of hlyBA and hlyA were reduced about threefold following oxygen exposure and treatment with hydrogen peroxide. Taken together, these results suggest that iron and oxidative stress have an effect on the control of hlyBA and hlyA transcriptional levels. A hlyBA mutant was constructed, and its hemolytic activity was greatly diminished compared to those of the hlyIII mutant and parent strains. In addition, the hlyBA mutant had a significant modification in colony morphology and growth deficiency compared to the parent strain. The implications of these findings for the pathophysiology of B. fragilis in extraintestinal infections and competition in ecological systems for this organism are discussed. Originally published Infection and Immunity, Vol. 74, No. 4, Apr 2006en_US
dc.identifier.citationInfection and Immunity; 74:4 p. 2304-2316en_US
dc.identifier.doi10.1128/IAI.74.4.2304-2316.2006
dc.identifier.pmidPMC1418898en_US
dc.identifier.urihttp://hdl.handle.net/10342/3388en_US
dc.language.isoen_USen_US
dc.publisherEast Carolina Universityen_US
dc.relation.urihttp://iai.asm.org/cgi/content/abstract/74/4/2304en_US
dc.rightsAuthor notified of opt-out rights by Cammie Jennings prior to upload of this article.en_US
dc.subjectBacteroides fragilisen_US
dc.subjectHemolysinsen_US
dc.subjectSynergistic activityen_US
dc.titleCharacterization of Bacteroides fragilis Hemolysins and Regulation and Synergistic Interactions of HlyA and HlyBen_US
dc.typeArticleen_US
ecu.journal.issue4
ecu.journal.nameInfection and Immunity
ecu.journal.pages2304-2316
ecu.journal.volume74

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