title: Human Serum-Specific Activation of Alternative Sigma Factors, the Stress Responders in Aggregatibacter actinomycetemcomitans.
abstract: Aggregatibacter actinomycetemcomitans, a known pathogen causing periodontal disease and infective endocarditis, is a survivor in the periodontal pocket and blood stream; both environments contain serum as a nutrient source. To screen for unknown virulence factors associated with this microorganism, A. actinomycetemcomitans was grown in serum-based media to simulate its in vivo environment. Different strains of A. actinomycetemcomitans showed distinct growth phenotypes only in the presence of human serum, and they were grouped into high- and low-responder groups. High-responders comprised mainly serotype c strains, and showed an unusual growth phenomenon, featuring a second, rapid increase in turbidity after 9-h incubation that reached a final optical density 2- to 7-fold higher than low-responders. Upon further investigation, the second increase in turbidity was not caused by cell multiplication, but by cell death. Whole transcriptomic analysis via RNA-seq identified 35 genes that were up-regulated by human serum, but not horse serum, in high-responders but not in low-responders, including prominently an alternative sigma factor rpoE (σE). A lacZ reporter construct driven by the 132-bp rpoE promoter sequence of A. actinomycetemcomitans responded dramatically to human serum within 90 min of incubation only when the construct was carried by a high responder strain. The rpoE promoter is 100% identical among high- and low-responder strains. Proteomic investigation showed potential interactions between human serum protein, e.g. apolipoprotein A1 (ApoA1) and A. actinomycetemcomitans. The data clearly indicated a different activation process for rpoE in high- versus low-responder strains. This differential human serum-specific activation of rpoE, a putative extra-cytoplasmic stress responder and global regulator, suggests distinct in vivo adaptations among different strains of A. actinomycetemcomitans.
authors.affiliation: Department of Molecular Physiology and Biophysics, College of Medicine, University of Vermont, Burlington, VT, United States of America.
authors.forename: Gaoyan
authors.initials: G
authors.lastname: Tang-Siegel
authors.affiliation: Department of Microbiology, University of Washington, Seattle, WA, United States of America.
authors.forename: Roger
authors.initials: R
authors.lastname: Bumgarner
authors.affiliation: Department of Molecular Physiology and Biophysics, College of Medicine, University of Vermont, Burlington, VT, United States of America.
authors.forename: Teresa
authors.initials: T
authors.lastname: Ruiz
authors.affiliation: Systems Biology and Bioinformatics Research Group, Pilot Plant Development and Training Institute, King Mongkut's University of Technology Thonburi, Bangkok, Thailand.
authors.forename: Weerayuth
authors.initials: W
authors.lastname: Kittichotirat
authors.affiliation: Ostrow School of Dentistry, University of Southern California, Los Angeles, CA, United States of America.
authors.forename: Weizhen
authors.initials: W
authors.lastname: Chen
authors.affiliation: Ostrow School of Dentistry, University of Southern California, Los Angeles, CA, United States of America.
authors.forename: Casey
authors.initials: C
authors.lastname: Chen
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D020869:Gene Expression Profiling; D017930:Genes, Reporter; D006801:Humans; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D011401:Promoter Regions, Genetic; D040901:Proteomics; D012329:RNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017423:Sequence Analysis, RNA; D065288:Serogroup; D044967:Serum / Q000737:chemistry*; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D016632:Apolipoprotein A-I; D001426:Bacterial Proteins; D003470:Culture Media; D012329:RNA, Bacterial; D012808:Sigma Factor