Deoxyribonucleic Acid Relatedness of Chlamydia sp. Strain TWAR to Chlamydia trachomatis and Chlamydia psittaci

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Abstract
Chlamydia sp. strain TWAR is an important cause of acute respiratory disease in humans. To determine the genetic relatedness of the TWAR organism to Chlamydia trachomatis and Chlamydia psittaci, solution hybridization followed by SI nuclease assays were performed, and guanine-plus-cytosine (G+C) contents were determined. Deoxyribonucleic acid (DNA) preparations from three TWAR isolates were radioactively labeled and hybridized against DNAs from three serovars ofC. trachomatis and five strains of C. psittaci. Reciprocal experiments were also done by using radioactively labeled C. trachomatis and C. psittaci DNAs against TWAR DNA. In all cases, the degree of DNA relatedness between TWAR and the two Chlamydia species was 10% or less. Within the group of TWAR isolates, there was 94% or greater sequence similarity. The G+C values for TWAR were intermediate between the G+C values for C. trachomatis and C. psittaci. The degrees of DNA relatedness among the strains within the species C. psittaci ranged from 20 to 100%.