The transformation efficiency was low after 5 min incubation with peptide, maximal after 15 min, and then declined to zero by 45 min, suggesting that feedback mechanisms and/or changes in the bacterial density lead to a rapid loss of the capacity for DNA uptake or recombination. The large yield of transformants obtained after such brief exposure to DNA indicates that S. suis possesses the capacity for a high level of natural competence, with an efficient DNA uptake mechanism. For this purpose, we used linear PCR-amplified DNA fragments containing a spectinomycin resistance cassette flanked by sequences identical to 59 and 39 coding regions of the S. suis apuA gene. To investigate the influence of the length of the homologous flanking DNA on transformation efficiency, the homologous flanking DNA region was varied in length from 250 to 1500 nucleotides. S. suis was transformed with the purified PCR products at the concentration of 10 mg/ml in triplicate experiments. The strong positive influence of the length of the flanking homologous segments on integration efficiency, similar to that reported previously for S. pneumoniae, suggests that the mechanism of recombination resembles that in S. pneumoniae, and provides a practical guide for design of gene-replacement donors in S. suis. Representative EMD534085 inhibitor species of the mitis, salivarius, mutans, pyogenic, and bovis phylogenetic clusters of streptococci have all been shown to control activity of ComX, a master regulator of bacterial competence, via small peptide pheromones. Here we show that S. suis, a streptococcal species which does not appear to fall within any of these phylogenetic clusters, also responds to a peptide pheromone by developing competence for DNA transformation. This finding does suggest that additional streptococcal species might also regulate competence via peptide pheromones. The competence system in S. suis was discovered by searching the genome for the conserved promoter elements found upstream of comX and comS in S. thermophilus and S. mutans. Two such promoter regions were JI-101 inhibitor identified in the S. suis genome. Downstream of one promoter we identified a homologue of comX, the alternative sigma factor that plays a fundamental role in the competence system in S. thermophilus and S. mutans.