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

We describe the expression and regulation of the gene sfaX II located near the Sfa II fimbrial determinant inthe newborn meningitis Escherichia coli (NMEC) isolate IHE3034. sfaX II belongs to a gene family, the 17-kDa genes, typically located downstream (300–3000 bp) of different fimbrial operons found in E. coli isolates of uropathogenic and newborn meningitis origin. Using transcriptional sfaX II reporter genefusions we found that different environmental conditions commonly affecting expression of fimbrialgenes also affected sfaX II expression. Analysis of the sfaX II transcripts showed that the gene is part of themain 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 downregulationby the nucleoid protein H-NS. Studies with an sfaX II mutant derivative of IHE3034 did notreveal 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 caninfluence 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.