P51 amino acid sequence variations among Neorickettsia sequences. Dendrograms of P51 from (A) a 41-aa fragment (counting all insertions) including the majority of predicted external loop 2 with 43 sequences and (B) a 31-aa fragment (counting all insertions) including the entire predicted external loop 4 with 36 sequences are shown with bootstrap values greater than 50.0% for 1000 replicates. *, bootstrap value of 90.0% or greater. East/Midwest US, sequences from states in the Eastern and Midwestern US. Pacific coast, sequences from Japan, Malaysia, and US states bordering the Pacific Ocean. GenBank accession numbers for P51 sequences are listed in Tables 1 and 2.