Phylogenetic analysis of mycoplasma strain ISM1499 and its assignment to the Acholeplasma oculi strain cluster

A mycoplasma strain designated ISM1499 was used to develop a mycoplasma genetic system (G. G. Mahairas and F. C. Minion, J. Bacteriol. 171:1775-1780, 1989; G. G. Mahairas, C. Jian, and F. C. Minion, Gene 93:61-65, 1990), but phenotypic inconsistencies led to the conclusion that this organism had been classified incorrectly as a member of the species Mycoplasma pulmonis. Studies were initiated to determine the proper taxonomic position of ISM1499, and on the basis of the results of our genetic analysis, this strain was assigned to the Acholeplasma oculi strain cluster. The base composition of strain ISM1499 was identical to the base composition of A. oculi 19L, but not to the base composition of Acholeplasma laidlawii PG8 (28.3 and 30.7 mol% G+C, respectively). The taxonomic position of ISM1499 was examined by performing a parsimony analysis with 16S ribosomal DNA sequence data, and the results were compared with previous phylogenetic reconstructions. Our results indicated that ISM1499 is more closely related phylogenetically to A. oculi 19L than to A. laidlawii PG8 and JA1. Heterogeneity in the 16S ribosomal DNA sequences of A. oculi 19L and ISM1499 and in the 16S ribosomal DNA sequences of A. laidlawii PG8 and JA1 may indicate that unusual dissimilarities occur in the 16S ribosomal DNA sequences of members of the genus Acholeplasma.