Analyses of Glucosyltransferase Gene of Streptococcus orisuis Isolated from Pig

Objectives: Streptococcus mutans and Streptococcus sobrinus have different water insoluble glucan-producing glucosyltransferase (gtf) gene (gtfB and gtfI, respectively). Recently, Streptococcus orisuis (d) and serovar strain were isolated and characterized from pig. It was supposed that these strain possessed gtf genes by PCR. The aim of this study was sequence and phylogenetic analyses of gtf genes from S. orisuis (d) and serovar strain. Methods: Inverse PCR coupled with direct sequencing was carried out to determine of the nucleotide sequence of gtf gene from S. orisuis (d). Then, new primer set was designed, and the expected 5.0-kb PCR products were amplified from serovar strain. Phylogenetic tree was constructed based on deduced amino acid sequences from various streptococcal GTFs. Results: The gtf gene of S. orisuis (d) consisted of a 4,398 bp open reading frame encoding for a 1,466 amino acids, and was revealed to belong to the gtfI group. The homology of amino acid sequence of the GTF-I from S. orisuis (d) and serovar strain was 98%, and this score ranges from 77 to 78% when compared to S. sobrinus. The N-terminal amino acid sequence was responsible for the secretion of GTF-I protein in S. orisuis (d) and serovar strain with high similarity to known other streptococcal GTFs. In addition, two other conserved regions, i.e., N-terminal putative catalytic domain and C-terminal glucan binding domain, were also found in GTF-Is of S. orisuis (d) and serovar strain. Phylogenetic analysis suggested that S. orisuis (d) and serovar strain, closely related to each other, resemble S. downei and S. sobrinus. Conclusion: GtfI genes of S. orisuis (d) and serovar strain were showed high homogeny in S. sobrinus and S. downei. This investigation was supported in part by the Ministry of Education, Culture, Sports, Science, and Technology to promote multi-disciplinary research projects (2003).