Diversity of the fsr-gelE Region of the Enterococcus faecalis Genome but Conservation in Strains with Partial Deletions of the fsr Operon

Division of Infectious Disease, Department of Medicine, University of Texas Medical School, Houston, TX 77030, USA.
Applied and Environmental Microbiology (Impact Factor: 3.67). 01/2011; 77(2):442-51. DOI: 10.1128/AEM.00756-10
Source: PubMed


Most Enterococcus faecalis isolates carry gelE, but many are gelatinase nonproducers due to the lack of fsrC (EF_1820) to EF_1841 (fsrC-EF_1841; 23.9 kb in strain V583), including most of the locus encoding Fsr, which activates gelE expression. Analysis of 22 accessible E. faecalis genomes revealed the identity of the 53-amino-acid propeptide of fsrD across multiple MLSTs (multilocus sequence types), although 12 distinctly different variations were found in the EF_1814-to-EF_1902
region. Diversity was seen in fsrABC, in the region EF_1814 to EF_1902, and in a 700-kb region surrounding fsrC-EF_1841. However, analysis of five sequenced strains carrying the fsrC-EF_1841 deletion and the putative integrative conjugative element efaB5 showed almost identical single nucleotide polymorphisms
(SNPs) in gelE and an identical junction sequence, despite their unrelated MLSTs, in contrast to those shown by strains without the deletion.
Further analysis confirmed the conserved gelE SNPs in 6 additional strains (11 in total) with the deletion. While we were unable to detect evidence of spontaneous deletion
using OG1RF and 8 other strains, we were able to engineer a deletion of the 37-kb fsrC-EF_1841 region of OG1RF without deleterious effects, and the 37-kb mutant showed changes in biofilm and chaining similar
to those shown by fsr-gelE mutants. In conclusion, we describe the identity of fsrD despite high plasticity within the fsrC-EF_1841 region and the surrounding sequence. However, strains lacking the fsrC-EF_1841 region show a distinct conservation of the sequence surrounding this deletion and in gelE, suggesting that the deletion may result from horizontal transfer and recombination.

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    • "The high plasticity of the E. faecalis genome in the area of the Fsr system has been indicated previously (Galloway-Pena et al. 2011). The gelatinase-negative phenotype has been reported for both natural and laboratory E. faecalis strains (Teixeira et al. 2012). "
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    ABSTRACT: Enterococcus faecalis is one of the most controversial species of lactic acid bacteria. Some strains are used as probiotics, while others are associated with severe and life-threatening nosocomial infections. Their pathogenicity depends on the acquisition of multidrug resistance and virulence factors. Gelatinase, which is required in the first steps of biofilm formation, is an important virulence determinant involved in E. faecalis pathogenesis, including endocarditis and peritonitis. The gene that codes for gelatinase (gelE) is controlled by the Fsr quorum-sensing system, whose encoding genes (fsrA, fsrB, fsrC, and fsrD) are located immediately upstream of gelE. The integration of a DNA fragment into the fsr locus of a derived mutant of E. faecalis V583 suppressed the gelatinase activity and prevented biofilm formation. Sequence analysis indicated the presence of IS256 integrated into the fsrC gene at nucleotide position 321. Interestingly, IS256 is also associated with biofilm formation in Staphylococcus epidermidis and Staphylococcus aureus. This is the first description of an insertion sequence that prevents biofilm formation in E. faecalis.
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    • "Previous studies have clearly demonstrated the genetic variance of the fsrABDC-gelE-sprE locus resulting from deletion of the 23.9 kb EF_1841-fsrC region and have demonstrated the correlation between this deletion and the lack of gelatinase activity [10], [11], [13], [15]. More recently, a larger study testing a diverse set of multilocus sequence types (MLSTs) demonstrated that the EF_1841-fsrC deletion was highly conserved with common single nucleotide polymorphisms (SNPs) and junction sequences in strains bearing the deletion; its association with the absence of gelatinase expression was shown to be independent of genetic lineage [15]. "
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