M. Konai

Revised group classification of the genus Spiroplasma

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-1T) (group XXVI), Spiroplasma lineolae (strain TALS-2T) (group XXVII), Spiroplasma platyhelix (strain PALS-1T) (group XXVIII), Spiroplasma montanense (strain HYOS-1T) (group XXXI), Spiroplasma helicoides (strain TABS-2T) (group XXXII) and Spiroplasma tabanidicola (strain TAUS-1T) (group XXXIII). Also, group XVII, which became vacant when strain DF-1T (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 files (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-1 (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 at 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.

Spiroplasma platyhelix sp. nov., a new mollicute with unusual morphology and genome size from the dragonfly Pachydiplax longipennis

Spiroplasma strain PALS-1T from the gut of the dragonfly Pachydiplax longipennis was shown to be distinct from other species, groups, and subgroups of the genus Spiroplasma as determined by reciprocal serological metabolism inhibition and deformation tests. However, this strain cross-reacted extensively with representatives of other groups when it was used as an antigen. Electron microscopy of cells of strain PALS-1T revealed cells surrounded by a single cytoplasmic membrane. Light microscopy revealed helical cells that exhibited twisting motility rather than rotatory or flexing motility. Variations in the tightness of coiling were transmitted from one end of the helix to the other. The strain was resistant to penicillin, which confirmed that no cell wall was present. The organism grew well in M1D and SP-4 liquid media under either aerobic or anaerobic conditions. Growth also occurred in 1% serum fraction medium and in conventional horse serum medium. The optimum temperature for growth was 30 degrees C, at which the doubling time was 6.4 h. Multiplication occurred at temperatures from 10 to 32 degrees C. Strain PALS-1T catabolized glucose and hydrolyzed arginine but not urea. The guanine-plus-cytosine content of the DNA was 29 +/- 1 mol%. The genome size was 780 kbp, the smallest genome size in the genus Spiroplasma. Strain PALS-1 (= ATCC 51748) is designated the type strain of a new species, Spiroplasma platyhelix.

Serologic and Genomic Relatedness of Group VIII and Group XVII Spiroplasmas and Subdivision of Spiroplasma Group VIII into Subgroups

Spiroplasmas are currently classified in a group system. Criteria for separation of the twenty-four currently designated groups include serologic relatedness, polyacrylamide gel electrophoretic patterns of proteins, guanine-plus-cytosine base ratios, and, in some cases, DNA-DNA homology. The analysis of DNA-DNA homology and serologic data from a large array of strains recently discovered in dipteran insects reveals that group VIII strain EA-1 from a syrphid fly, strain TAAS-1 from a horse fly, and group XVII strain DF-1 from a deer fly belong to a large complex (supergroup) of strains with various degrees of interrelatedness. Strains DF-1 and EA-1 share DNA-DNA homology of 33 to 48% (high-stringency conditions), while strain TAAS-1 shares 42 to 67% homology with DF-1 and EA-1. The strains had temperature optima of 30 to 37°C, but the temperature minima and maxima reflected the geographic region of strain origin. These three strains also share G+C values of about 30 mol%, utilize arginine, and tend to grow in culture to very high titers (1011 cells per ml). The helical cells of these strains are smaller than those of other spiroplasmas and readily pass through filter pores of 220 nm. These data support the taxonomic placement of the biotypes represented by strains EA-1, DF-1, and TAAS-1 into one supergroup, group VIII, with subgroups designated as VIII-1, VIII-2, and VIII-3, respectively. It is proposed that group XVII remain vacant.

Division of group XVI spiroplasmas into subgroups

Some group XVI spiroplasmas, such as strains CC-1 (Spiroplasma cantharicola) and CB-1, are associated with cantharid beetles. Fifteen related but heterogeneous strains have been isolated from mosquitoes, other insects, and a flower in France and the United States. In the present study, these seventeen strains have been compared by deformation and metabolism inhibition serological tests, by one-dimensional protein sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and by determination of the guanine-plus-cytosine content of their DNA. Five of the 17 strains were further compared by DNA-DNA hybridization and by restriction enzyme (EcoRI and HindIII) analysis of their DNA. On the basis of the resulting data, we propose that group XVI be subdivided into three subgroups. Subgroup XVI-I is represented by strain CC-1 (ATCC 43207) from a cantharid beetle in the United States, and strain MQ-6 from a wasp; subgroup XVI-2 is represented by strain CB-1 (ATCC 43208) from a cantharid beetle and two strains from mosquitoes, all in the United States; and subgroup XVI-3 is represented by strain Ar-1357 (ATCC 51126) and contains 11 strains from mosquitoes and 1 strain from a flower, all from the Savoy region of France.

Spiroplasma chrysopicola sp. nov., Spiroplasma gladiatoris sp. nov., Spiroplasma helicoides sp. nov., and Spiroplasma tabanidicola sp. nov., from Tabanid (Diptera: Tabanidae) Flies

Four spiroplasma strains, DF-1T, TG-1T, TABS-2T, and TAUS-1T, all of which were isolated from deerflies or horseflies (Diptera: Tabanidae), were serologically distinct from previously described spiroplasma species, groups, and subgroups. Strain DF-1Toriginated from a Maryland deerfly (Chrysops sp.); strain TG-1Twas isolated from a Maryland horsefly (Tabanus gladiator); strain TAUS-1Toriginated from a member of the Tabanus abdominalis-limbatinevris complex of horseflies collected in Maryland; and strain TABS-2Twas isolated from a horsefly (Tabanus abactor) collected in Oklahoma. Cells of all of the strains appeared to be helical and motile when they were examined by dark-field microscopy. Cells of strain DF-1Tgrowing in M1D medium were short helices with less than six turns; the helical cells of the other strains were long and usually had six or more turns. The short cells of strain DF-1Tpassed through 450- and 300-nm filter pores with no reduction in titer, but the longer cells of the other strains were partially retained by 450-nm-pore-size filters. Electron microscopic examination of all of the strains revealed wall-less cells surrounded only by a single cytoplasmic membrane. All of the strains grew well in SP-4 liquid media and in conventional mycoplasma or M1D media supplemented with horse or fetal bovine serum. Strains TABS-2T, TAUS-1T, and DF-1Trequired serum or sterol for growth, but strain TG-1Twas able to grow in the absence of serum or sterol. The optimum temperatures for growth of the four strains varied from 30 to 32°C, and growth occurred at 10 to 37°C. All of the strains catabolized glucose but did not hydrolyze urea. Only strain DF-1Thydrolyzed arginine. The guanine-plus-cytosine contents of the DNAs of the strains were: DF-1T, 29 ± 1 mol%; TG-1T, 26 ± 1 mol%; TABS-2T, 27 ± 1 mol%; and TAUS-1T, 26 ± mol%. The genome sizes of strains DF-1Tand TAUS-1Twere 1,270 and 1,375 kbp, respectively. Strain DF-1 (= ATCC 43209), the representative of spiroplasma subgroup VIII-2, is designated the type strain of a new species, Spiroplasma chrysopicola. We also propose that strain TG-1T(= ATCC 43525T), the designated representative of group XXIII, should be placed in a new species, Spiroplasma gladiatoris. In addition, group XXXII spiroplasma strain TABS-2 (= ATCC 51746) is designated the type strain of Spiroplasma helicoides sp. nov., and group XXXIII representative strain TAUS-1 (= ATCC 51747) is designated the type strain of another new species, Spiroplasma tabanidicola.

Spiroplasma leptinotarsae sp. nov., a mollicute uniquely adapted to its host, the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae).

Spiroplasma strain LD-1T (T = type strain), which was isolated from the gut of a Colorado potato beetle (Leptinotarsa decemlineata) larva collected in Maryland, was serologically distinct from other spiroplasmas. Similar isolates were obtained from other L. decemlineata specimens collected in various parts of North America, in Poland, and in other eastern European countries and from Leptinotarsa texana specimens collected in Texas. Cells of strain LD-1T, which in early passages were spiral, exhibited exceptionally rapid translational motility. This rapid motility and the spiral shape were lost after extended passage in culture. The organism required serum for growth. Originally isolated in coculture with insect cells in DCCM medium, strain LD-1T adapted to several media in the absence of cocultured cells. Use of anaerobic conditions allowed primary isolation in a variety of media. The organism did not grow in serum-free media containing 2% serum fraction. Optimal growth in M1D medium occurred at 30 to 37°C (doubling time, 7.2 h). On solid M1D medium containing 2.0% Noble agar (pH 6.25) at 30°C, strain LD-1T produced discrete colonies with numerous satellites. Strain LD-1T hydrolyzed arginine, but did not utilize urea; there was evidence of weak fermentation of glucose. The guanine-plus-cytosine content of the DNA was determined to be 25 ± 1 mol%, and the genome size was 1,085 kb. The results of extensive studies of the ecology of this spiroplasma suggest that it is host specific for Leptinotarsa beetles. Strain LD-1 (= ATCC 43213) is designated the type strain of a new species, Spiroplasma leptinotarsae.

Spiroplasma velocicrescens sp. nov., from the vespid wasp Monobia quadridens

Spiroplasma strain MQ-4T (T = type strain), which was isolated from the hemolymph of the vespid wasp Monobia quadridens, was serologically distinct from other spiroplasma species, groups, putative groups, and subgroups. Each strain MQ-4T cell was helical and motile and was surrounded by a single cytoplasmic membrane; there was no evidence of a cell wall. The strain grew well in 1% serum fraction medium, as well as in SM-1, M1D, and SP-4 liquid media, under both aerobic and anaerobic conditions. Strain MQ-4T grew at temperatures ranging from 10 to 41 degrees C but did not grow at 43 degrees C. The strain grew optimally at 37 degrees C with a doubling time of 0.6 h, the shortest doubling time recorded for any spiroplasma. Strain MQ-4T catabolized glucose and arginine but did not hydrolyze urea. The guanine-plus-cytosine content of the DNA was about 27.5 +/- 1 mol%. The genome size was 1,480 kbp (940 MDa). Strain MQ-4 (= ATCC 35262) is designated the type strain of a new species, Spiroplasma velocicrescens.

Spiroplasma corruscae sp. nov., from a firefly beetle (Coleoptera: Lampyridae) and tabanid flies (Diptera: Tabanidae).

Spiroplasma strain EC-1T (T = type strain), which was isolated from the gut of a lampyrid beetle (Ellychnia corrusca) in Maryland, was serologically distinct from other spiroplasma species and groups. Similar strains were obtained from other E. corrusca specimens, and, later, numerous isolates of similar or partially related strains were obtained from several species of tabanid files. Cells of strain EC-1T were helical, motile filaments that were bound by a single cytoplasmic membrane, and there was no evidence of a cell wall. The cells were filterable through 220-nm-pore-size membrane filters but not through 100-nm-pore-size membrane filters. The organism was absolutely resistant to penicillin (1,000 U/ml) and required sterol for growth. Strain EC-1T grew well in M1D and SP-4 liquid media and could be cultivated in the Edward formulation of conventional mycoplasma medium and in 1% serum fraction medium. Optimal growth occurred at 32 degrees C (doubling time, 1.5 h). Strain EC-1T multiplied at 10 to 41 degrees C, but not at 5 or 43 degrees C. This organism produced acid from glucose, but did not hydrolyze arginine or utilize urea. The guanine-plus-cytosine content of the DNA was determined to be 26.3 mol% by the melting temperature method and 27.0 mol% by the buoyant density method. As a result of our studies, strain EC-1 (= ATCC 43212) is designated the type strain of a new species, Spiroplasma corruscae.

Spiroplasma syrphidicola sp. nov., from a Syrphid Fly (Diptera: Syrphidae)

Spiroplasma sp. strain EA-1(T) (T = type strain) (subgroup VIII-1), which was isolated from the syrphid fly Eristalis arbustorum, was serologically distinct from other spiroplasma species, groups, and subgroups, The cells of this strain, as revealed by dark-field light microscopy, were short, helical, and motile. An electron microscopic examination revealed wall-less cells delimited by a single membrane. The unusually short cells passed through 220-nm filter pores with no reduction in titer. The organisms grew well in SM-1, M1D, and SP-4 liquid media. Growth also occurred in conventional horse serum medium and 1% serum fraction medium. Strain EA-1(T) grew at temperatures between 10 and 41 degrees C, and optimum growth occurred at 32 degrees C. The doubling time at the optimal temperature was 1.0 h. The strain catabolized glucose and hydrolyzed arginine but did not hydrolyze urea. The guanine-plus-cytosine content of the DNA was 30 +/- 1 mol%. The genome size was about 1,230 kbp. Strain Ea-1 (= ATCC 33826), which represents subgroup VIII-1, is designated the type strain of a new species, Spiroplasma syrphidicola.

Spiroplasma monobiae sp. nov. from the Vespid Wasp Monobia quadridens (Hymenoptera : Vespidae)

Spiroplasma strain MQ-1T (T = type strain) from the hemolymph of the vespid wasp Monobia quadridens differed serologically from other spiroplasma species, groups, and subgroups. Cells of strain MQ-1T were helical and motile and possessed a single cytoplasmic membrane, with no evidence of a cell wall. The organism grew in conventional mycoplasma medium, in serum fraction, SM-1, M1D, and SP-4 liquid media, and on SP-4 solid medium in either aerobic or anaerobic environments. The optimum temperature for growth was 32°C, but multiplication occurred over a wide temperature range (10 to 37°C). The doubling time at 32°C in M1D medium was 1.9 h. Strain MQ-1T catabolized glucose but hydrolyzed neither arginine nor urea. Previous work showed that strain MQ-1T has a unique methylase, previously known only in eucaryotes. Also, strain MQ-1T induces production of tumor necrosis factor in bone marrow macrophages. The guanine-plus-cytosine content of the DNA was 28 ± 1 mol%. The genome size of strain MQ-1T was 940 kb (627 MDa); a similar strain, MQ-8, had a genome size of 985 kb (657 MDa). Strain MQ-1T and its allies have the smallest genomes known in the genus Spiroplasma. Strain MQ-1 (=ATCC 33825) is designated the type strain of a new species, Spiroplasma monobiae.