Phylogenetic and complementation analysis of a single-stranded dna binding protein family from lactococcal phages indicates a non-bacterial origin

• Main Authors: Szczepankowska , Agnieszka K. (INRA Institut National de la Recherche AgronomiqueInstitute of Biochemistry and Biophysics PAS, Jouy-en-JosasWarsaw(France). UMR1319 Institut MicalisDepartment of Microbial Biochemistry), Prestel , Eric (INRA , Jouy-En-Josas (France). UMR 1319 MICrobiologie de l'ALImentation au Service de la Santé Humaine), Mariadassou , Mahendra (INRA , Jouy-En-Josas (France). UR 1077 Mathématique, Informatique et Génome), Bardowski , Jacek K. (Institute of Biochemistry and Biophysics PAS, Warsaw(Pologne). Department of Microbial Biochemistry), Bidnenko , Elena(auteur de correspondance) (INRA , Jouy-En-Josas (France). UMR 1319 MICrobiologie de l'ALImentation au Service de la Santé Humaine)
• Format: Publication
• Language: English
• Published: 2011
• Subjects: analyse phylogénique; bactérie; escherichia coli; famille de protéine; gene-transfer; identification

Background: The single-stranded-nucleic acid binding (SSB) protein superfamily includes proteins encoded by different organisms from Bacteria and their phages to Eukaryotes. SSB proteins share common structural characteristics and have been suggested to descend from an ancestor polypeptide. However, as other proteins involved in DNA replication, bacterial SSB proteins are clearly different from those found in Archaea and Eukaryotes. It was proposed that the corresponding genes in the phage genomes were transferred from the bacterial hosts. Recently new SSB proteins encoded by the virulent lactococcal bacteriophages (Orf14bIL67-like proteins) have been identified and characterized structurally and biochemically. Methodology/Principal Findings: This study focused on the determination of phylogenetic relationships between Orf14bIL67-like proteins and other SSBs. We have performed a large scale phylogenetic analysis and pairwise sequence comparisons of SSB proteins from different phyla. The results show that, in remarkable contrast to other phage SSBs, the Orf14bIL67–like proteins form a distinct, self-contained and well supported phylogenetic group connected to the archaeal SSBs. Functional studies demonstrated that, despite the structural and amino acid sequence differences from bacterial SSBs, Orf14bIL67 protein complements the conditional lethal ssb-1 mutation of Escherichia coli. Conclusions/Significance: Here we identified for the first time a group of phages encoded SSBs which are clearly distinct from their bacterial counterparts. All methods supported the recognition of these phage proteins as a new family within the SSB superfamily. Our findings suggest that unlike other phages, the virulent lactococcal phages carry ssb genes that were not acquired from their hosts, but transferred from an archaeal genome. This represents a unique example of a horizontal gene transfer between Archaea and bacterial phages.