Genetic Relatedness Among the Typhus Group of Rickettsiae

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Abstract
The taxonomy of the typhus biogroup (Rickettsia prowazekii and R. mooseri [R. typhi]) of the genus Rickettsia and Rochalimaea quintana has been studied on the basis of the guanine plus cytosine content of the respective deoxyribonucleic acids (DNAs), the genome size, and the degree of DNA-DNA hybridization. The previously published guanine plus cytosine values for certain strains are confirmed, and the guanine plus cytosine values are described for some additional strains in each species. The genome sizes of four strains of R. prowazekii, three strains of R. mooseri, and two strains of R. quintana were very similar and averaged approximately 109 daltons. The various strains within the species boundaries hybridized at nearly the 100% level. The DNAs of various strains of R. prowazekii hybridized with the DNAs of various strains of R. mooseri rather consistently at the level of 70 to 77%. The DNAs of two strains of Rochalimaea quintana hybridized with those of R. prowazekii Breinl and R. mooseri Wilmington in the range of 25 to 33%.