Characterization of a new peptide transport system in Streptococcus thermophilus

• Di-tripeptide transport system
• Gene acquisition by horizontal transfer event
• Proteolytic surface system

In silico analysis of the genome of Streptococcus thermophilus LMD-9 revealed that this strain has a potential new peptide/nickel ABC transporter. We named this system OTS for Oligopeptide Transporter of S. thermophilus. It is composed of a peptide/nickel binding protein OtsA, two permeases OtsB and OtsC and a double ATPase OtsD. This system was presumably acquired by horizontal transfer from Actinobacteria or distant species like Lactococcus raffinolactis or Enterococcus asini may be via an intermediate like Lactococcus lactis or its ancestor. RT-PCR experiments proved that OTS gene cluster is transcribed and that at least the otsB, otsC, and otsD genes constitute an operon. A mutant LMD-9Δots, partially deleted for the otsA and otsB genes was constructed. Growth of LMD-9 and LMD-9Δots strains was monitored in the presence of different nitrogen sources and in the presence of urea and nickel. Results revealed that OTS is not implicated in nickel transport, but constitutes a new characterized transporter of peptides of small size, possibly di- and tripeptides in S. thermophilus.

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