Our understanding of the genetic and molecular basis underlying bacterial adhesion to host cells is of great clinical importance and may help design therapeutic strategies for the control of bacterial infections. The bacteria Microbacterium nematophilum and Yersinia pestis and Y. pseudotuberculosis cause disease in C. elegans after attaching to the surface of the worm. Our laboratories have independently isolated alleles of
bus-12 and
bus-4 in genetic screens for resistance to these bacteria. We cloned these genes and showed that BUS-12 is a multi-spanning transmembrane protein with homology to UDP-glucuronic acid/UDP-N-acetylgalactosamine transporters and the human Solute carrier family 35 member D3, whereas BUS-4 is member of the galactosyltransferase GT31 family, which includes BRE-2, BRE-5 and SQV-2. We have also cloned
bus-2 and assigned it to the same galactosyltransferase family. Although
bus-2 mutants have been isolated only from the M. nematophilum screens, they exhibit resistance to both bacterial pathogens. One allele of
bus-12 (
br5) behaves genetically as null and bears a deletion that removes most of the BUS-12 coding region and an adjoining gene. The second allele (
e2740), is a weaker allele with respect to bacterial adhesion, and appears to contain a complex DNA rearrangement yet to be characterized. Additional mutations are being sought. Like the mutations in the
srf-3 locus, (disrupting another nucleotide sugar transporter),
bus-12 mutants are mildly skiddy and show no morphological defects. Unexpectedly, some
srf-3 bus-12 double mutants show novel synthetic phenotypes: they become Egl and Unc, and their growth is severely impaired at 15oC. We are currently trying to identify by RNAi further putative genetic interactions with other nucleotide sugar transporters encoded in the genome of C. elegans.Transgenic lines bearing extrachromosomal arrays comprising the entire
bus-12 gene have proven very difficult to maintain, suggesting that overexpression of this nucleotide sugar transporter can be deleterious to the worm. A
bus-12::DsRed2 promoter fusion exhibits expression in the head in the socket and muscle cells, in a couple of neurons in the nerve ring, in the seam cells and the intestine. However, a less complex expression pattern is observed for the glycosyltransferases
bus2 and
bus-4::GFP operon reporters which express specifically in the seam cells.