Background: Streptococcus macedonicus is an intriguing streptococcal species whose most frequent source of isolation is fermented foods similarly to Streptococcus thermophilus. During the genome sequencing of S. macedonicus ACA-DC 198 a plasmid was identified.
Objectives: To analyse pSMA198, the first plasmid isolated from S. macedonicus and to shed light onto its acquisition path.
Methods: Similarity searches of nucleotide and protein sequences, comparative analysis of whole plasmid sequences and phylogenetic analysis were performed using the appropriate bioinformatics tools.
Methods: Based on the similarity profiles of the plasmid’s replication initiation protein (Rep) and its origin of replication (ori), pSMA198 belongs to the narrow host range pCI305/pWV02 family found primarily in lactococci and it is the first such plasmid to be reported in streptococci. Comparative analysis of the pSMA198 over its ori, origin of transfer (oriT) or entire length revealed a high degree of similarity with plasmids pSK11b, pVF22 and pIL5, respectively, all isolated from Lactococcus lactis strains from milk or milk products. Phylogenetic analysis of the pSMA198 Rep showed that the vast majority of closely related proteins derive from lactococcal dairy isolates.
Conclusions: Our findings demonstrate that S. macedonicus ACA-DC 198 acquired most probably plasmid pSMA198 from L. lactis during an ancestral genetic exchange event that took place in milk or dairy products. Based on our analysis we provide the first molecular and evolutionary evidence for the habituation of S. macedonicus to the dairy environment.
