[Frontiers in Bioscience 7, d619-640, March 1, 2002]


Gail E. Gasparich

Department of Biological Sciences, Towson University, 8000 York Road, Towson, MD 21252


1. Abstract
2. Introduction
3. Spiroplasma taxonomy
3.1. General characteristics of Spiroplasmas
3.2. Taxonomy requirements for classification of Spiroplasmas
3.2.1. Required biological, molecular and serological characterization
3.2.2. Group designation
3.2.3. Subgroup designation
3.3. Some problems with serologically-based taxonomy
3.4. Use of 16S rDNA sequence analysis in Spiroplasma taxonomy
3.5. Polyphasic classification in Spiroplasma taxonomy
3.6. Current classification of Spiroplasmas
4. Diversity
4.1. Host range
4.2. General diversity
5. Evolution
5.1. Evolution of Spiroplasmas in relation to other major groups of Eubacteria
5.1.1. Clostridium lineage
5.1.2. Mollicute lineage
5.2. Spiroplasma phylogeny
5.2.1. Major spiroplasma clade descriptions: Spiroplasma citri cluster
5.2.2. Major spiroplasma clade descriptions: Spiroplasma apis cluster
5.2.3. Major spiroplasma clade descriptions: Mycoplasma mycoides cluster
5.2.4. Major spiroplasma clade descriptions: Spiroplasma ixodetis cluster
5.2.5. Problems with 16S rDNA sequence analysis for Spiroplasma phylogenetic determinations
5.2.6. Problem with Mycoplasma mycoides cluster
5.3. Spiroplasma genome sequencing projects
5.3.1. Spiroplasma citri project
5.3.2. Spiroplasma kunkelii project
6. Adaptation
6.1. Host cell specificity
6.1.1. Strict specificity
6.1.2. General specificity
6.1.3. Host cell attachment
6.2. Host interactions: pathogenicity
6.2.1. Insect host diseases
6.2.2. Insect vectored plant diseases
6.2.3. Unusual sex-ratio disorders
6.2.4. Spiroplasmas infections of animals
6.2.5. Spiroplasmas and Creutzfeldt-Jakob disease and scrapie
6.3. Host interactions: commensalistic relationships
6.4. Host interactions: mutualistic relationships
7. Perspective
8. Acknowledgements
9. References


Since its designation as a separate genus some 30 years ago, Spiroplasmas have been well documented in a wide range of hosts and as the causative agent of several plant and insect diseases. One major area of research is the continued identification and taxonomical characterization of new Spiroplasma sp. combined with a determination of phylogenetic relationships among the various Spiroplasma sp. and between the Spiroplasmas and other members of the Mollicutes and Eubacteria. Although most phylogenetic analyses have been dependent on 16S rDNA sequence data, progress in two Spiroplasma sp. genome sequencing projects will provide new genomic regions for comparative focus. The co-evolution of Spiroplasmas with their arthropod hosts has provided an additional research focus to study host specificity and attachment. The diversity of symbiotic relationships between Spiroplasmas and their hosts has led to the study of commensal, mutualistic, and pathogenic relationships. Pathogenesis in insect hosts or in plants, transferred by insect hosts, is a major research focus, which requires attachment and invasion into insect tissues beyond the initial infection site, and successful movement to other tissues. The diversity and adaptations that have occurred during the evolution of the Spiroplasmas with their hosts will be the primary focus of this article.