A survey of genomic diversity in Enterococcus faecalis by microarray based comparative 1 genomic hybridization 2

1 We have compared nine Enterococcus faecalis strains with E. faecalis V583 (V583), for 2 which a complete genome sequence and a genome-wide microarray is available. The strains 3 we have used in this study (the test strains) originated from various environments; 4 veterinarian, food, and environmental isolates, as well as lab strains. Comparative genomic 5 hybridization using microarrays (CGH) is a powerful and promising tool for obtaining novel 6 information on genome diversity in bacteria. By CGH one obtains clues about which genes 7 are present or divergent in the strains studied, compared to a reference strain, here V583. 8 Information obtained by CGH is important, both in an ecological and in a systematic point of 9 view. CGH of E. faecalis showed considerable diversity in gene content. The main variation 10 was found in regions corresponding to exogenously acquired or mobile DNA in V583. 11 Antibiotic resistance genes, virulence factors, integrated plasmid genes were among the genes 12 that were deemed divergent in most of the test strains. The extensive transport and metabolic 13 capabilities of V583 appeared similar in the test strains; CGH indicated that the ability to 14 transport and metabolize various carbohydrates was similar in the test strains, which was 15 further verified by API 50 CH assays. The content of genes related to stress tolerance 16 appeared similar in V583 and the nine test strains, supporting the view of E. faecalis as an 17 organism able to resist harsh conditions. This study showed interesting evolutionary trends in 18 E. faecalis and is the first survey of whole genome diversity in the species. 19 3 INTRODUCTION 1