title: Genome sequence of Lactobacillus helveticus, an organism distinguished by selective gene loss and insertion sequence element expansion.
abstract: Mobile genetic elements are major contributing factors to the generation of genetic diversity in prokaryotic organisms. For example, insertion sequence (IS) elements have been shown to specifically contribute to niche adaptation by promoting a variety of genetic rearrangements. The complete genome sequence of the cheese culture Lactobacillus helveticus DPC 4571 was determined and revealed significant conservation compared to three nondairy gut lactobacilli. Despite originating from significantly different environments, 65 to 75% of the genes were conserved between the commensal and dairy lactobacilli, which allowed key niche-specific gene sets to be described. However, the primary distinguishing feature was 213 IS elements in the DPC 4571 genome, 10 times more than for the other lactobacilli. Moreover, genome alignments revealed an unprecedented level of genome stability between these four Lactobacillus species, considering the number of IS elements in the L. helveticus genome. Comparative analysis also indicated that the IS elements were not the primary agents of niche adaptation for the L. helveticus genome. A clear bias toward the loss of genes reported to be important for gut colonization was observed for the cheese culture, but there was no clear evidence of IS-associated gene deletion and decay for the majority of genes lost. Furthermore, an extraordinary level of sequence diversity exists between copies of certain IS elements in the DPC 4571 genome, indicating they may represent an ancient component of the L. helveticus genome. These data suggest a special unobtrusive relationship between the DPC 4571 genome and its mobile DNA complement.
authors.affiliation: Moorepark Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland.
authors.forename: Michael
authors.initials: M
authors.lastname: Callanan
authors.forename: Pawel
authors.initials: P
authors.lastname: Kaleta
authors.forename: John
authors.initials: J
authors.lastname: O'Callaghan
authors.forename: Orla
authors.initials: O
authors.lastname: O'Sullivan
authors.forename: Kieran
authors.initials: K
authors.lastname: Jordan
authors.forename: Olivia
authors.initials: O
authors.lastname: McAuliffe
authors.forename: Amaia
authors.initials: A
authors.lastname: Sangrador-Vegas
authors.forename: Lydia
authors.initials: L
authors.lastname: Slattery
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Fitzgerald
authors.forename: Tom
authors.initials: T
authors.lastname: Beresford
authors.forename: R Paul
authors.initials: RP
authors.lastname: Ross
mesh_terms: D001483:Base Sequence; D002876:Chromosomes, Bacterial; D017124:Conserved Sequence; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics*; D017353:Gene Deletion; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D052198:Lactobacillus helveticus / Q000235:genetics*; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D026801:Synteny
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial