Genetic basis of the variability of nitrate reduction trait in Yersinia pestis strains

The genetic basis of the varying ability to reduce nitrate in strains belonging to different biovars and subspecies of plague-causing microbe has been investigated and the inability to reduce nitrate observed in different intraspecies groups of Yersinia pestis has been shown to stem from mutations in different genes involved in the expression of this trait. The absence of denitrifying activity in strains of altaica and hissarica subspecies was not due to a mutation at position 613 of the periplasmic reductase napA observed in the strains of the biovar medievalis of the main subspecies, but rather was due to a mutation in the sequence encoding the nitrate-binding domain of the ABC transporter protein SsuA; a thymine insertion (+T) was detected at position 302 from the start of the ssuA gene. Five strains of biovar antiqua isolated at different times in Mongolia, China, and Africa were shown to lack the ability to reduce nitrate. A PCR test targeting two chromosomal regions containing deletions of 19 and 24 bp in size has been developed for the identification of strains of the biovar medievalis. This test can be combined with the test for the marker mutation in the napA gene for a more reliable detection of Y. pestis strains belonging to this biovar.