The pga gene cluster in Aggregatibacter actinomycetemcomitans is necessary for the development of natural competence in Ca(2+) -promoted biofilms.
Natural competence is the ability of bacteria to incorporate extracellular DNA into their genomes. This competence is affected by a number of factors, including Ca(2+) utilization and biofilm formation. As bacteria can form thick biofilms in the presence of extracellular Ca(2+) , the additive effects of Ca(2+) -promoted biofilm formation on natural competence should be examined. We evaluated natural competence in Aggregatibacter actinomycetemcomitans, an important periodontal pathogen, in the context of Ca(2+) -promoted biofilms, and examined whether the pga gene cluster, required for bacterial cell aggregation, is necessary for competence development. The A. actinomycetemcomitans cells grown in the presence of 1 mm CaCl2 exhibited enhanced cell aggregation and increased levels of cell-associated Ca(2+) . Biofilm-derived cells grown in the presence of Ca(2+) exhibited the highest levels of natural transformation frequency and enhanced expression of the competence regulator gene, tfoX. Natural competence was enhanced by the additive effects of Ca(2+) -promoted biofilms, in which high levels of pga gene expression were also detected. Mutation of the pga gene cluster disrupted biofilm formation and competence development, suggesting that these genes play a critical role in the ability of A. actinomycetemcomitans to adapt to its natural environment. The Ca(2+) -promoted biofilms may enhance the ability of bacteria to acquire extracellular DNA.
Division of Oral Rehabilitation, Department of Periodontology, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
K
K
Hisano
O
O
Fujise
M
M
Miura
T
T
Hamachi
E
E
Matsuzaki
F
F
Nishimura
D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D018441:Biofilms / Q000254:growth & development*; D002118:Calcium / Q000378:metabolism*; D005798:Genes, Bacterial; D005809:Genes, Regulator; D005810:Multigene Family
D001426:Bacterial Proteins; D002118:Calcium
Aggregatibacter actinomycetemcomitans; biofilm; calcium; natural competence; pga gene cluster