Twenty-eight strains of spiroplasma subgroup I-2 isolated from insects and flower surfaces were similar in their serological properties. Strain BC-3 (T = type strain), which was isolated from the honeybee, was chosen as a representative of this cluster and was characterized according to accepted standards. This strain and other strains of the cluster entered the hemocoel of their insect hosts after per os acquisition, caused pathology in various tissues, and reduced adult longevity. Growth in SM-1 or M1D medium occurred at 20 to 37°, with optimum growth at about 32 to 35°. Cholesterol was required for growth. Glucose, fructose, and other carbohydrates were fermented, and arginine was catabolized. Seventeen strains, including strain BC-3, reacted with considerable homogeneity in deformation tests and were completely separable from strains of subgroup I-1 () and subgroup I-3 (corn stunt spiroplasma). A group of five subgroup I-2 strains showed homogeneity upon one-dimensional polyacrylamide gel electrophoresis of cell proteins. Strain BC-3 was also serologically distinct from subgroups I-4 through I-8; from , and ; and from representative strains of spiroplasma groups II and VI through XI. Previously published studies on strain BC-3 and related strains demonstrated that (i) these organisms comprise a unique subgroup of the complex (group I); (ii) deoxyribonucleic acid-deoxyribonucleic acid homologies between strain BC-3 and strains of other group I subgroups do not exceed 70%; (iii) the patterns of protein sharing among group I strains revealed by two-dimensional polyacrylamide gel electrophoresis support molecular genetic indications of partial relatedness; (iv) the RI restriction endonuclease patterns of deoxyribonucleic acids from strain BC-3 and serologically related strains show close relatedness; (v) sequencing of 5S ribosomal ribonucleic acid suggests some degree of relatedness with all organisms now classified in the ; (vi) strain BC-3 is capable of viscotactic and chemotactic responses; (vii) strain BC-3 possesses fibrils that may mediate various types of motility; and (viii) a lytic virus (SpV4) isolated from sp. strain B63 (a representative of subgroup I-2) is morphologically and genomically distinct from other spiroplasma viruses and forms plaques only on lawns of subgroup I-2 spiroplasmas. Previous work on strain AS 576, another member of subgroup I-2, demonstrated (i) a viscotactic response, (ii) moderate sensitivity to osmotic environments, (iii) susceptibility to tetracycline and aminoglycoside antibiotics, (iv) growth in a relatively simple, chemically defined medium, (v) nutritional utilization patterns in defined medium, and (vi) a genome molecular weight of 10. On the basis of our new findings and the previously described properties of strain BC-3 and related subgroup I-2 strains, we propose that spiroplasma strains with the characteristics described here be classified as a new species, . Strain BC-3, the type strain, has been deposited in the American Type Culture Collection as strain ATCC 33219.


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