Open AccessHuman Serum-Specific Activation of Alternative Sigma Factors, the Stress Responders in Aggregatibacter actinomycetemcomitans
Author(s) -
Gaoyan G Tang-Siegel,
Roger E. Bumgarner,
Teresa Ruíz,
Weerayuth Kittichotirat,
Weizhen Chen,
Casey Chen
Publication year - 2016
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0160018
Subject(s) - aggregatibacter actinomycetemcomitans , microbiology and biotechnology , sigma factor , biology , virulence , virulence factor , gene expression , gene , promoter , bacteria , genetics , porphyromonas gingivalis
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 ( σ E ). 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 .