A truncated lag-1 gene was found in the strain Görlitz 6543 (mAb-subgroup Bellingham) as recently reported [49]. The whole gene is present but carries a mutated start codon. Since Görlitz 6543 showed no reactivity with mAb 3/1 it was assumed that the mutation significantly impairs the production of a functional O-acetyltransferase. Phylogenetic analysis showed 99.9% BKM120 nmr amino acid similarity of Görlitz 6543 to Corby (mAb-subgroup Knoxville), 130b and Lens

(both mAb-subgroup Benidorm) (Figure  2A). Figure 2 Dendrogram of variable ORFs. Multiple amino acid based cluster analysis using UPGMA (BioNumerics, Applied Maths NV, Belgium). The phylogenetic trees of gene lag-1 and of the ORFs 6, 7 and 8 are shown. ORF 9 is identical to the phylogenetic tree of ORF 8 and is therefore not shown. Similarity values and branch distances

were depicted in percentages [%]. The strain-specific mAb-subgroup is indicated in brackets. The mutated start codon of lag-1 of Görlitz 6543 was neglected for similarity analysis and is indicated with †. ABC-transporter genes wzt and wzm as Sg1-specfic marker region Noticeable conserved genes within the heterogenic region were wzt (ORF 4) and wzm (ORF 5) which are almost identical among all analyzed Sg1 strains (Figure  1A, Table  3). Wzm encodes for a protein containing a transmembrane domain while wzt encodes for a nucleotide ATR inhibitor binding domain of an ABC transporter system which mediates the O-antigen translocation across the inner membrane [50]. Recently, both genes were evaluated as marker genes for PCR based Chlormezanone discrimination between L. pneumophila Sg1 and non-Sg1 strains [35]. The ABC transporter-dependent O-antigen pathway interacts with WecA

(ORF 14), an UDP-GlcNAc-1-transferase which initiates O-chain biosynthesis at the cytoplasmic site of the inner membrane [50]. The low amino acid similarity of WecA between Sg1 and non-Sg1 that was described recently KU-57788 combined with the absence of wzm and wzt in non-Sg1 genomes [35] indicate a different O-chain biosynthesis mechanism for non-Sg1 strains than found in Sg1 strains. ORF 6 through 11 involved in O-antigen modification The most variable region within the Sg1-specific region in terms of low similarities on the amino acid level and the diverse arrangement of single ORFs was found from ORF 6 to ORF 11. The strains of mAb-subgroup Benidorm 130b and Lens were almost identical regarding the amino acid similarities of the single ORFs within the Sg1-specific region. Interestingly, strain 130b carried a large inverted fragment containing ORF 7 to ORF 11 (Figure  1A). This region was surrounded by transposases suggesting their potential contribution to the inversion. Since the strain 130b showed no altered reactivity pattern using the Dresden panel compared to other Benidorm strains it could be stated that the inversion had no detectable effect on the LPS phenotype detected by monoclonal antibodies. The adjacent ORF 6 showed a high degree of variability between L.