AEM Accepts, published online ahead of print on 30 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01845-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Interstrain genomic comparison reveals a crucial role for IS elements in the evolution of Lactobacillus helveticus.

Pawel Kaleta, John O'Callaghan, Gerald F. Fitzgerald, Thomas P. Beresford^*, and R. Paul Ross

Teagasc, Moorepark Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland; Alimentary Pharmabiotic Centre, Cork, Ireland; Department of Microbiology, University College Cork, Ireland

^* To whom correspondence should be addressed. Email: tom.beresford{at}teagasc.ie.

Lactobacillus helveticus is a versatile diary bacterium found to possess heterogeneous genotypes depending on ecosystem it is being isolated from. The recently published genome sequence showed a remarkable flexibility of its structure, demonstrated by a substantial level of IS element expansion in association with massive gene decay. To assess this diversity and examine the level of genome plasticity within the Lb. helveticus species, an array based comparative genome hybridization (aCGH) experiment was designed in which 10 strains were analysed. The aCGH revealed sixteen clusters of open reading frames (ORFs) flanked by IS elements. Four of these ORFs are associated with restriction/modification which may have played a role in accelerated evolution of strains in a commercially intensive ecosystem undoubtedly challenged through successive phage attack. Furthermore, analysis of the IS-flanked clusters demonstrated that the most frequently encountered IS were also those most abundant in the genome (IS1201, ISL2, ISLhe1, ISLhe2, ISLhe65 and ISLhe63). These findings contribute to the overall viewpoint on a versatile character of IS elements and the role they may play in bacterial genome plasticity.