title: Fermentable-sugar-level-dependent regulation of leukotoxin synthesis in a variably toxic strain of Actinobacillus actinomycetemcomitans.
abstract: Actinobacillus actinomycetemcomitans, a Gram-negative periodontopathic bacterium, produces a leukotoxin belonging to the RTX family. The production of leukotoxin varies greatly among different strains of this species and under different culture conditions. A toxin-production-variable strain, 301-b, stably produces significant amounts of leukotoxin in anaerobic fructose-limited chemostat cultures, but does not do so in the presence of excess fructose. This communication describes the cloning and sequencing of the leukotoxin promoter region from 301-b, showing that this strain has a promoter region similar to that from strain 652, a moderately toxic strain. Northern blot analysis using a leukotoxin gene probe demonstrated that change in toxin production in response to the level of external fructose was due to alteration in the transcriptional level of the leukotoxin gene. Pulsing of fructose into the fructose-limited chemostat culture remarkably reduced the intracellular cAMP level from 40 pmol (mg dry wt cells)(-1) to 3.1 pmol (mg dry wt cells)(-1), which was restored when the culture was returned to fructose-limited conditions. Further, it was found that addition of external cAMP to the culture with excess fructose resulted in an apparent recovery of leukotoxin production. Taken together, these findings indicate that a cAMP-dependent mechanism, possibly a catabolite-repression-like system, may be involved in the regulation of leukotoxin production in this bacterium.
authors.affiliation: Departments of Microbiology1, Preventive Dentistry2 and Periodontology and Endodontology3, Okayama University Dental School, Shikata-cho 2-chome, Okayama 700-8525, Japan.
authors.forename: Tetsuyoshi
authors.initials: T
authors.lastname: Inoue
authors.affiliation: Departments of Microbiology1, Preventive Dentistry2 and Periodontology and Endodontology3, Okayama University Dental School, Shikata-cho 2-chome, Okayama 700-8525, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tanimoto
authors.affiliation: Departments of Microbiology1, Preventive Dentistry2 and Periodontology and Endodontology3, Okayama University Dental School, Shikata-cho 2-chome, Okayama 700-8525, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Tada
authors.affiliation: Departments of Microbiology1, Preventive Dentistry2 and Periodontology and Endodontology3, Okayama University Dental School, Shikata-cho 2-chome, Okayama 700-8525, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Ohashi
authors.affiliation: Departments of Microbiology1, Preventive Dentistry2 and Periodontology and Endodontology3, Okayama University Dental School, Shikata-cho 2-chome, Okayama 700-8525, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Fukui
authors.affiliation: Laboratory of Microbial Ecology, Department of Bioresource Science, Ibaraki University School of Agriculture, Ami-machi, Ibaraki 300-0393, Japan4.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D000693:Anaerobiosis; D003470:Culture Media; D000242:Cyclic AMP / Q000378:metabolism; D005098:Exotoxins / Q000096:biosynthesis* / Q000235:genetics; D005285:Fermentation; D005632:Fructose / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D003470:Culture Media; D005098:Exotoxins; C018579:leukotoxin; D005632:Fructose; D000242:Cyclic AMP