Natural transformation in mesophilic and thermophilic bacteria: Identification and characterization of novel, closely related competence genes in Acinetobacter sp strain BD413 and Thermus thermophilus HB27

The mesophile Acinetobacter sp, strain BD413 and the extreme thermophile Th ermus thremophilus HB27 display high frequencies of natural transformation. In this study we identified and characterized a novel competence gene in A cinetobacter sp, strain BD413, com;l, whose product displays significant si milarities to the competence proteins ComA and ComEC in Neisseria and Bacil lus species, Transcription of comA correlated with growth phase-dependent t ranscriptional regulation of the recently identified pilin-like factors of the transformation machinery. This finding strongly suggests that comA is p art of a competence regulon, Examination of the genome sequence of T, therm ophilus HB27 led to detection of a comA/comEC-like open reading frame (ORF) which is flanked by an ORF whose product shows significant similarities to the Bacillus subtilis competence protein ComEA. To examine whether these t wo ORFs, designated comEC and comEA, are implicated in natural transformati on of T, thermophilus HB27, both were disrupted by using a thermostable kan a-mycin resistance marker, Natural transformation in comEC mutants was redu ced 1,000-fold, whereas in comEA mutants the natural transformation phenoty pe was completely eliminated. These results strongly suggest that both gene s, comEC and comEA, are required far natural transformation in T, thermophi lus HB27, Several transmembrane cr-helices are predicted based on the amino acid sequences of ComA in Acinetobacter sp, strain BD413 and ComEC in T, t hermophilus HB27, which suggests that ComA and ComEC are located in the inn er membrane and function in DNA transport through the cytoplasmic membrane.