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 sero logic relatedness, polyacrylamide gel electrophoretic patterns of prot eins, guanine-plus-cytosine base ratios, and, in some cases, DNA-DNA h omology. The analysis of DNA-DNA homology and serologic data from a la rge array of strains recently discovered in dipteran insects reveals t hat group VIII strain EA-1 from a syrphid fly, strain TAAS-1 from a ho rse fly, and group XVII strain DF-1 from a deer fly belong to a large complex (supergroup) of strains with various degrees of interrelatedne ss. Strains DF-1 and EA-1 share DNA-DNA homology of 33 to 48% (high-st ringency conditions), while strain TAAS-1 shares 42 to 67% homology wi th DF-I and EA-1. The strains had temperature optima of 30 to 37-degre es-C, but the temperature minima and maxima reflected the geographic r egion of strain origin. These three strains also share G+C values of a bout 30 mol%, utilize arginine, and tend to grow in culture to very hi gh titers (10(11) cells per ml). The helical cells of these strains ar e smaller than those of other spiroplasmas and readily pass through fi lter pores of 220 nm. These data support the taxonomic placement of th e biotypes represented by strains EA-1, DF-1, and TAAS-1 into one supe rgroup, group VIII, with subgroups designated as VIII-1, VIII-2, and V III-3, respectively. It is proposed that group XVII remain vacant.