title: Global transcriptional profiling of Burkholderia pseudomallei under salt stress reveals differential effects on the Bsa type III secretion system.
abstract: BACKGROUND
  Burkholderia pseudomallei is the causative agent of melioidosis where the highest reported incidence world wide is in the Northeast of Thailand, where saline soil and water are prevalent. Moreover, recent reports indicate a potential pathogenic role for B. pseudomallei in cystic fibrosis lung disease, where an increased sodium chloride (NaCl) concentration in airway surface liquid has been proposed. These observations raise the possibility that high salinity may represent a favorable niche for B. pseudomallei. We therefore investigated the global transcriptional response of B. pseudomallei to increased salinity using microarray analysis.
  
  
  RESULTS
  Transcriptome analysis of B. pseudomallei under salt stress revealed several genes significantly up-regulated in the presence of 320 mM NaCl including genes associated with the bsa-derived Type III secretion system (T3SS). Microarray data were verified by reverse transcriptase-polymerase chain reactions (RT-PCR). Western blot analysis confirmed the increased expression and secretion of the invasion-associated type III secreted proteins BipD and BopE in B. pseudomallei cultures at 170 and 320 mM NaCl relative to salt-free medium. Furthermore, salt-treated B. pseudomallei exhibited greater invasion efficiency into the lung epithelial cell line A549 in a manner partly dependent on a functional Bsa system.
  
  
  CONCLUSIONS
  B. pseudomallei responds to salt stress by modulating the transcription of a relatively small set of genes, among which is the bsa locus associated with invasion and virulence. Expression and secretion of Bsa-secreted proteins was elevated in the presence of exogenous salt and the invasion efficiency was enhanced. Our data indicate that salinity has the potential to influence the virulence of B. pseudomallei.
authors.affiliation: Department of Immunology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Pornpan
authors.initials: P
authors.lastname: Pumirat
authors.forename: Jon
authors.initials: J
authors.lastname: Cuccui
authors.forename: Richard A
authors.initials: RA
authors.lastname: Stabler
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Stevens
authors.forename: Veerachat
authors.initials: V
authors.lastname: Muangsombut
authors.forename: Ekapot
authors.initials: E
authors.lastname: Singsuksawat
authors.forename: Mark P
authors.initials: MP
authors.lastname: Stevens
authors.forename: Brendan W
authors.initials: BW
authors.lastname: Wren
authors.forename: Sunee
authors.initials: S
authors.lastname: Korbsrisate
mesh_terms: D016957:Burkholderia pseudomallei / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D003470:Culture Media; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride; D013312:Stress, Physiological; D014158:Transcription, Genetic
chemical_list: D003470:Culture Media; D012965:Sodium Chloride