The spontaneous Legionella pneumophila lipopolysaccharide (LPS) mutant 137,
which did not bind the LPS-specific mAb 2625, was complemented with a geno
mic library from the parental wild-type strain. Transformants were screened
for reconstitution of the wild-type LPS phenotype, able to bind mAb 2625.
By this strategy, a 32,661 bp region comprising 30 open reading frames (Orf
s) was identified. Orfs with significant homologies to genes encoding enzym
es required for LPS or capsule biosynthesis of Gram-negative bacteria were
located on the gene locus. The mutation of strain 137 could be assigned to
a deletion of a cytosine residue in Orf 8. The protein encoded by Orf 8 exh
ibited homology to bacterial methyl-transferases. The L. pneumophila LPS ge
ne locus included genes with deduced products likely to be involved in LPS
core oligosaccharide biosynthesis (rmlA-D, rhamnosyl-transferases, acetyl-t
ransferase) as well as LPS O-chain biosynthesis and translocation (mnaA, ne
uB, neuA, wecA, wzt, wzm). The neuA (Orf 25) and neuB (Orf 24) gene product
s were functionally characterized by complementation of the capsule negativ
e E. coli K1 mutants EV5 and EV24, respectively. By introduction of the L.
pneumophila neuA gene into E. coli EV5 and the neuB gene into EV24, express
ion of the K1 polysialic acid capsule could be restored. We, therefore, con
clude that the biosynthesis pathway of legionaminic acid, the structural un
it of the L. pneumophila Sg1 O-antigen, might be similar to the biosynthesi
s of sialic acid. Southern blot analysis indicated the entire gene locus to
be present in L. pneumophila serogroup (Sg)1 strains, whereas only parts o
f the DNA stretch hybridized to DNA from Sg2 to Sg14 strains.