Significant changes have been made in the systematics of the genus Spiroplasma (class Mollicutes) since it was expanded by revision in 1987 to include 23 groups and eight sub-groups. Since that time, two additional spiroplasmas have been assigned group numbers and species names. More recently, specific epithets have been assigned to nine previously designated groups and three sub-groups. Also, taxonomic descriptions and species names have been published for six previously ungrouped spiroplasmas. These six new organisms are : Spiroplasma alleghenense (strain PLHS-13 (group XXVI), Spiroplasma lineolae (strain TALS-23 (group XXVII), Spiroplasma platyhelix (strain PALS-13 (group XXVlll), Spiroplasma montanense (strain HYOS-13 (group XXXI), Spiroplasma helicoides (strain TABS-23 (group XXXII) and Spiroplasma tabanidicola (strain TAUS-13 (group XXXIII). Also, group XVII, which became vacant when strain DF-IT (Spiroplasma chrysopicola) was transferred to group VIII, has been filled with strain Tab 4c. The discovery of these strains reflects continuing primary search in insect reservoirs, particularly horse flies and deer flies (Diptera :Tabanidae). In the current revision, new group designations for 10 spiroplasma strains, including six recently named organisms, are proposed. Three unnamed but newly grouped spiroplasmas are strain TIUS-I (group XXIX; ATCC 51751) from a typhiid wasp (Hymenoptera : Tiphiidae), strain BIUS-1 (group XXX; ATCC 51750) from floral surfaces of the tickseed sunflower (Bidens sp.) and strain BARC 1901 (group XXXIV; ATCC 700283). Strain BARC 2649 (ATCC 700284) from Tabanus lineola has been proposed as a new sub-group of group VIII. Strains TIUS-1 and BIUS-1 have unusual morphologies, appearing as helices a t only certain stages in culture. In this revision, potentially important intergroup serological relationships observed between strain DW-1 (group II) from a neotropical Drosophila species and certain sub-group representatives of group I spiroplasmas are also reported.
Progenies from some wild-caught females of Drosophila willistoni and three other sibling species are entirely female. The proclivity for production of unisexual female progeny by these flies was named the sex ratio (SR) trait and was originally thought to be genetic. However, experiments in the laboratory of Donald F. Poulson in the early 1960s demonstrated that this 'trait' was vertically transmitted and infectious, in that it could be artificially transferred by injection from infected females to non-infected females. Motile, helical micro-organisms were observed in females showing the trait. In 1979, the SR organisms were designated as group II in the informal spiroplasma classification system. The organisms proved to be extremely fastidious, but were eventually cultivated in a very complex cell-free medium (H-2) after initial co-cultivation with insect cells. Cultivation in the H-2 medium and the subsequent availability of a triply cloned strain (DW-19 permitted comparative studies. Cells of strain DW-lT were helical, motile filaments 200-250 nm in diameter and were bound by a single trilaminar membrane. Cells plated on 1.8% Noble agar formed small satellite-free colonies 60-70 pm in diameter with dense centres and uneven edges. The temperature range for growth was 26-30 "C; optimum growth occurred a t 30 "C, with a doubling time in H-2 medium of 15.8 h. The strain passed through filters with 220 nm, but not 100 nm, pores. Reciprocal serological comparisons of strain DW-lT with representatives of other spiroplasma groups showed an extensive pattern of one-way crossing when strain DW-lT was used as antigen. However, variable, usually low-level reciprocal cross-reactions were observed between strain DWlT and representatives of group I sub-groups. The genome size of strain DW-lT was 2040 kbp, as determined by PFGE. The G+C content was 2621 mol%, as determined b y buoyant density and melting point methods. The serological and molecular data indicate that strain DW-lT is separated from group I representative strains sufficiently to justify retention of its group status. Continued group designation is also indicated by the ability of SR spiroplasmas to induce male lethality in Drosophila, their vertical transmissibility and their extremely fastidious growth requirements. Group II spiroplasmas, represented by strain DW-lT (ATCC 431 533, are designated Spiroplasma poulsonii.
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