title: Acquisition through horizontal gene transfer of plasmid pSMA198 by Streptococcus macedonicus ACA-DC 198 points towards the dairy origin of the species.
abstract: BACKGROUND
  Streptococcus macedonicus is an intriguing streptococcal species whose most frequent source of isolation is fermented foods similarly to Streptococcus thermophilus. However, S. macedonicus is closely related to commensal opportunistic pathogens of the Streptococcus bovis/Streptococcus equinus complex.
  
  
  RESULTS
  We analyzed the pSMA198 plasmid isolated from the dairy strain Streptococcus macedonicus ACA-DC 198 in order to provide novel clues about the main ecological niche of this bacterium. pSMA198 belongs to the narrow host range pCI305/pWV02 family found primarily in lactococci and to the best of our knowledge it is the first such plasmid to be reported in streptococci. Comparative analysis of the pSMA198 sequence revealed a high degree of similarity with plasmids isolated from Lactococcus lactis strains deriving from milk or its products. Phylogenetic analysis of the pSMA198 Rep showed that the vast majority of closely related proteins derive from lactococcal dairy isolates. Additionally, cloning of the pSMA198 ori in L. lactis revealed a 100% stability of replication over 100 generations. Both pSMA198 and the chromosome of S. macedonicus exhibit a high percentage of potential pseudogenes, indicating that they have co-evolved under the same gene decay processes. We identified chromosomal regions in S. macedonicus that may have originated from pSMA198, also supporting a long co-existence of the two replicons. pSMA198 was also found in divergent biotypes of S. macedonicus and in strains isolated from dispersed geographic locations (e.g. Greece and Switzerland) showing that pSMA198's acquisition is not a recent event.
  
  
  CONCLUSIONS
  Here we propose that S. macedonicus acquired plasmid pSMA198 from L. lactis via an ancestral genetic exchange event that took place most probably in milk or dairy products. We provide important evidence that point towards the dairy origin of this species.
authors.affiliation: Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Papadimitriou
authors.affiliation: Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece.
authors.forename: Rania
authors.initials: R
authors.lastname: Anastasiou
authors.affiliation: Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Maistrou
authors.affiliation: Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece; Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece.
authors.forename: Thomas
authors.initials: T
authors.lastname: Plakas
authors.affiliation: Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece.
authors.forename: Nikos C
authors.initials: NC
authors.lastname: Papandreou
authors.affiliation: Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece.
authors.forename: Stavros J
authors.initials: SJ
authors.lastname: Hamodrakas
authors.affiliation: Genoscreen, Service of Research, Development and Innovation in Health and Environment, Campus de l'Institut Pasteur, 1 rue du Professeur Calmette, 59000, Lille, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Ferreira
authors.affiliation: Genoscreen, Service of Research, Development and Innovation in Health and Environment, Campus de l'Institut Pasteur, 1 rue du Professeur Calmette, 59000, Lille, France; Institut Pasteur de Lille, Center for Infection and Immunity of Lille (CIIL), F-59019, Lille, France; Inserm U1019, F-59019, Lille, France; CNRS UMR8204, F-59019, Lille, France; Univ Lille de Nord France, F-59019, Lille, France.
authors.forename: Philip
authors.initials: P
authors.lastname: Supply
authors.affiliation: INRA, UMR1319 Micalis, Jouy-en-Josas, F-78352, France; AgroParisTech, UMR Micalis, Jouy-en-Josas, F-78352, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Renault
authors.affiliation: Institut Pasteur de Lille, Center for Infection and Immunity of Lille (CIIL), F-59019, Lille, France; Inserm U1019, F-59019, Lille, France; CNRS UMR8204, F-59019, Lille, France; Univ Lille de Nord France, F-59019, Lille, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Pot
authors.affiliation: Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece.
authors.forename: Effie
authors.initials: E
authors.lastname: Tsakalidou
mesh_terms: D000818:Animals; D002417:Cattle; D005516:Food Microbiology; D022761:Gene Transfer, Horizontal; D013294:Lactococcus lactis / Q000235:genetics / Q000302:isolation & purification*; D008892:Milk / Q000382:microbiology*; D010957:Plasmids / Q000235:genetics*; D013291:Streptococcus / Q000235:genetics / Q000302:isolation & purification*