EVOLUTIONARY ORIGIN OF A MONOPHASIC SALMONELLA SEROVAR, 9,12-L,V--, REVEALED BY IS200 PROFILES AND RESTRICTION FRAGMENT POLYMORPHISMS OF THE FLJB GENE

The emergence in several countries of the monophasic serogroup D1 sero var Salmonella 9,12:l,v:- provided the opportunity to study its evolut ionary origin. According to current models, such a variant serovar cou ld have arisen by horizontal transfer of a new flagellar gene to a pre existing monophasic Salmonella strain or, alternatively, by the loss o f the phase 2 flagellar gene of an originally biphasic Salmonella stra in. Five known serovars of Salmonella, S. panama, S. kapemba, S. goett ingen, S. zaiman, and S. mendoza, could have been possible ancestors o f the new variant. The profiles of the insertion element IS200, which has been shown to provide phylogenetic markers for serogroup D1 salmon ellae, were analyzed in relation to the restriction fragment length po lymorphisms of the phase 2 flagellar gene. Together they provide unequ ivocal evidence that Salmonella 9,12:l,v:- arose from a strain of S. g oettingen. Analysis of the flj operon of the variant indicated that lo ss of phase 2 flagellar antigen expression occurred through deletion o f the hin gene and adjacent DNA, thereby blocking the phase 2 flagella r gene in the off position.