Analysis of the sfaX(II) locus in the Escherichia coli meningitis isolate IHE3034 reveals two novel regulatory genes within the promoter-distal region of the main S fimbrial operon

Abstract

We describe the expression and regulation of the gene sfaX(II) located near the Sfa(II) fimbrial determinant in the newborn meningitis Escherichia coli (NMEC) isolate IHE3034. sfaX(II) belongs to a gene family, the 17-kDa genes, typically located downstream (300-3000bp) of different fimbrial operons found in E. coli isolates of uropathogenic and newborn meningitis origin. Using transcriptional sfaX(II) reporter gene fusions we found that different environmental conditions commonly affecting expression of fimbrial genes also affected sfaX(II) expression. Analysis of the sfaX(II) transcripts showed that the gene is part of the main fimbrial operon as it is transcribed together with the rest of the fimbrial genes. In addition, the sfaX(II) gene can be expressed from a more proximal promoter and is found to be subject to strong down-regulation by the nucleoid protein H-NS. Studies with an sfaX(II) mutant derivative of IHE3034 did not reveal effects on Sfa(II) fimbrial biogenesis as monitored by e.g. immunofluorescence microscopy. Nevertheless, a mutation in sfaX(II) resulted in altered expression of other surface components. Moreover, we define a new gene, sfaY(II), coding for a putative phosphodiesterase that is located in between the sfaX(II) gene and the fimbrial biogenesis genes. Our studies by ectopic expression of sfaY(II) in Vibrio cholerae showed that the gene product caused reduced biofilm formation and it is proposed that sfaY(II) can influence cyclic-di-GMP turnover in the bacteria. Our findings demonstrate that the operons typical for S-fimbriae of extraintestinal pathogenic E. coli include previously unrecognized novel regulatory genes.