Spiroplasmas: evolutionary relationships and biodiversity

Abstract

Spiroplasmas are wall-less descendants of Gram-positive bacteria that maintain some of the smallest genomes known for self-replicating organisms. These helical, motile prokaryotes exploit numerous habitats, but are most often found in association with insects. Co-evolution with their insect hosts may account for the highly speciose nature of the genus Spiroplasma, with many spiroplasmas existing in obligate insect/plant transmission cycles. In addition to insect and plant hosts, spiroplasmas are found in association with ticks and crustaceans. Although most spiroplasma associations appear to be commensal, some cases of pathogenicity or mutualism have been described. Most notably, spiroplasmas have been identified as the causative agents of agricultural and aquacultural diseases and the sex ratio disorder in insects. Some spiroplasmas exhibit strict host and/or geographical ranges, but others are relative generalists. Species of the genus Spiroplasma have been traditionally classified into 34 groups based on cross-reactivity of surface antigens. Three of the serogroups contain closely related strain complexes that are further divided into subgroups. Phylogenetic reconstructions based on 16S rDNA sequence strongly support the closely related serogroups. To date, less than 40 Spiroplasma species have been fully characterized and given binomial names. Complete characterization of a new species involves numerous phenotypic and genotypic tests as outlined in the minimal standards document; this document is currently under revision to include phylogenetic data and a reevaluated set of required phenotypic and genotypic tests. The area of spiroplasma research is poised for major advances with new criteria for naming species in preparation, a dramatic increase in available molecular characters, the promise of full genome sequences, and advances in genetic tools for manipulation of these organisms.

Use of oxytetracycline for the treatment of tremor disease in the Chinese mitten crab Eriocheir sinensis

“…However, TD caused by spiroplasma has become epidemic in farmed crab. Spiroplasma are wall-less Gram-positive bacteria and are amongst the smallest unicellular organisms in the world (Regassa & Gasparich 2006). The agent can pass through membrane filters with pores of 220 nm diameter and can be cultivated in M1D or R2 media in vitro (Tully et al 1977, Whitcomb 1983, Hackett et al 1987, Moulder et al 2002.…”

“…Subsequent isolation and analysis of the 16S rRNA gene, which was the 'gold standard' of microbiological classification, confirmed the agent to be a spiroplasma (Wang et al 2003b(Wang et al , 2004a. This was the first spiroplasma to be found in aquatic crustaceans and it began to change our understanding of the host range of these organisms (Christensen et al 2005, Regassa & Gasparich 2006). Koch's postulates were later fulfilled for the spiroplasma, providing definitive proof that this agent was the cause of TD (Wang et al 2004a).…”

Disease risks associated with the importation and release of non-native crayfish species into mainland Britain

“…Whilst it has not been possible in the current study to fully assess the effect of the infection on fecundity or survival, Spiroplasma spp. have been reported in a number of plant and animal hosts, and some are considered to act as male killing agents, distorting sex ratios (Nienhaus & Sikora 1979, Regassa & Gasparich 2006. In freshwater Crustacea, including crayfish, Spiroplasma spp.…”

Rapid polyvalent screening for largescale environmental Spiroplasma surveys

“…6 Antisera were produced for nonreactive and representative isolates; titers against antigenic homologues are indicated. 7 Strains or antisera are listed for reactions at titers >40. 8 One-way DF titers >320 allowed tentative serogroup placement; tentative isolate placement in a previously described serogroup generally served as the testing end-point.…”

“…There are currently 38 described serogroups (reviewed in 7; 14), and some of the groups are further subdivided. For example, group I has eight subgroups that include five characterized species (7). The serogroup I subgroups have 0.986-0.991 16S rDNA sequence similarity, yet distinctive serologies (5).…”