Evolutionary origin and radiation of the avian-adapted non-motile salmonellae

Institute of Molecular Evolutionary Genetics, Mueller Laboratory, Pennsylvania State University, University Park, Pennsylvania 16802, USA * Department of Medical Microbiology, University of Dundee Medical School, Ninewells Hospital, Dundee DD1 9SY Correspondence should be sent to Professor R. K. Selander. Received April 27, 1992 Accepted June 30, 1992 Multilocus enzyme electrophoresis was employed to estimate chromosomal genotypic diversity and relationships among 131 isolates of the non-motile Salmonella biotypes Gallinarum and Pullorum (serotype 1, 9, 12:–:–) that cause fowl typhoid and pullorum disease, respectively. Thirteen electrophoretic types (ETs), marking clones, were distinguished, and construction of a neighbour-joining phylogenetic tree revealed three lineages: one consisted of five ETs of Gallinarum, a second included seven ETs of Pullorum, and a third was represented by a single ET (Ga/Pu 1) that is intermediate between those of the other two lineages in both multilocus enzyme genotype and biochemical properties. Enzyme genotype analysis and comparative nucleotide sequencing of the phase 1 flagellin gene ( fliC ), the hook-associated protein 1 gene ( flgK ), and the 6-phosphogluconate dehydrogenase gene ( gnd ) identified serotype Enteritidis ( 1 , 9,12:g, m:–) as a close relative of the non-motile salmonellae. In most strains of biotype Gallinarum, the fliC gene is complete, intact and identical in sequence to that of Enteritidis, but isolates of three ETs had a stop codon at position 495. The fliC sequences of the ETs of Pullorum differed from that of Enteritidis in having non-synonymous changes in either two or three codons and a synonymous change in one codon. The sharing of distinctive alleles at three metabolic enzyme loci and a stop codon in flgK indicates that the non-motile salmonellae are monophyletic and that their most recent common ancestor was non-motile. Since diverging from that ancestor, the Pullorum lineage has evolved more rapidly than the Gallinarum and Ga/Pu 1 lineages.