f Unique clustering genes in the bacterial chromosome affecting the type-III secretion of enterohaemorrhagic Escherichia coli

Bioinformatics analysis was used to search for unknown genes that might influence the phenotypic presentations of enterohaemorrhagic Escherichia coli (EHEC). By so doing and using the known genomic data from EHEC O157  : H7 and K-12, it has been deduced that genes Z4863 to Z4866 of EHEC do not exist in K-12 strains. These four gene sequences have low degrees of homology (18–40 % amino acid identities) to a set of genes in K-12, which have been known to encode fatty acid biosynthesis enzymes. We referred these four consecutive genes as a fasyn cluster and found that deletion of fasyn from EHEC resulted in a defective type-III secretion (T3S). This deletion apparently did not decrease the amounts of the T3S proteins ectopically expressed from plasmids. Examination of the corresponding mRNAs by real-time PCR revealed that the mRNAs readily decreased in the fasyn-deleted mutant and this suppressive effect on the mRNA levels appeared to spread across all lee operons. Complementation with fasyn reverted the T3S-deficient phenotype. Furthermore, this reversion was also seen when the mutant was supplemented with locus of enterocyte effacement activators (Ler or GrlA). Thus, these unique clustering genes located apart from locus of enterocyte effacement on the bacterial chromosome also play a role in affecting T3S of EHEC.