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Spiroplasmas of Group I: the Spiroplasma citri cluster
Abstract:
We propose that Group I spiroplasmas be subdivided into seven, rather than four, subgroups. The seven subgroups showed remarkable homogeneity when several representative strains were compared. Hybridization reactions between DNAs of representative strains within subgroups were generally at least 90 percent, and usually at least 80 percent co-migrating cell proteins were found. In addition, when plasmid DNA was excluded, profiles of restricted DNA among strains within subgroups were very similar. In contrast, comparisons between Group I subgroups showed substantial heterogeneity. This heterogeneity was indicated by DNA-DNA hybridization reactions as low as 10-20 percent and only 10-15 percent co-migrating cell proteins. Spiroplasma citri (subgroup I-1), the honeybee spiroplasma (subgroup I-2), and the corn stunt spiroplasma (subgroup I-3) are all pathogenic organisms with more or less limited host ranges. Strains of these three subgroups have been repeatedly isolated from affected hosts. Since strains of subgroups I-2 and I-3 can be clearly differentiated from other Group I subgroups and all other spiroplasmas, the DNA-DNA hybridization reactions of the subgroups do not exceed 70 percent, and because they are important pathogens, we propose (subject to completion of standard requirements for species descriptions) that they be recognized as new species of the genus Spiroplasma.
Insights
This study proposes subdividing Group I spiroplasmas into seven subgroups, revealing high homogeneity within subgroups but significant diversity between them. Pathogenic subgroups I-2 and I-3 may represent new Spiroplasma species.
Area of Science:
- Microbiology
- Molecular Biology
- Bacteriology
Background:
- Group I spiroplasmas are a diverse group of plant and insect pathogens.
- Current classification recognizes four subgroups within Group I.
- Understanding spiroplasma diversity is crucial for disease management and taxonomy.
Purpose of the Study:
- To re-evaluate the classification of Group I spiroplasmas.
- To investigate the genetic relatedness and homogeneity within potential subgroups.
- To propose taxonomic revisions based on molecular data.
Main Methods:
- DNA-DNA hybridization assays to assess genetic similarity.
- Comparison of co-migrating cell proteins.
- Analysis of restricted DNA profiles, excluding plasmid DNA.
Main Results:
- Seven distinct subgroups within Group I were identified, showing high internal homogeneity (DNA-DNA hybridization >80%).
- Significant heterogeneity was observed between subgroups (DNA-DNA hybridization as low as 10-20%).
- Spiroplasma citri (I-1), honeybee spiroplasma (I-2), and corn stunt spiroplasma (I-3) demonstrated clear differentiation.
Conclusions:
- The proposed seven-subgroup classification reflects the molecular diversity within Group I spiroplasmas.
- Subgroups I-2 and I-3, due to their pathogenicity and genetic distinctness, are proposed as new species within the genus Spiroplasma.
- Further taxonomic validation is required for the proposed species recognition.