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Occurrence of extrachromosomal deoxyribonucleic acids in spiroplasmas associated with plants, insects, and ticks
G E Gasparich1, K J Hackett, E A Clark
1Insect Biocontrol Laboratory, USDA, Beltsville, Maryland 20705.
Abstract:
Several spiroplasmas (helical, motile mollicutes) were previously shown to contain extrachromosomal DNA (E-DNA) elements in the form of viruses (double-stranded viruses or the replicative form of single-stranded viruses) or plasmids. These elements are now being investigated as potential vectors for use in spiroplasma transformation systems. Described herein is the first extensive survey of spiroplasma E-DNA in 23 spiroplasma groups (30 strains), a study facilitated by improvements in protocols for E-DNA extraction. E-DNA elements were found in spiroplasmas associated with leafhoppers/plants (spiroplasma subgroups I-1, I-3, and I-8), other insects (subgroups I-2, I-5, I-6, and I-7 and groups IV and XXII), and ticks (subgroup I-4 and groups V and VI). Elements, maintained by passage with their host spiroplasmas, were often lost after extended passage. Whether the current distribution of E-DNA elements is indicative of historical or proximate factors is not known. Many elements (about 75%) from group I spiroplasmas hybridized with Spiroplasma citri viruses SpV1 or SpV3. Of the elements associated with other spiroplasma groups, none hybridized with either virus. These include Spiroplasma apis strains B31 (18 kb) and L89 (18 and 20 kb), S. mirum strains SMCA (20 kb) and Anderson (16 and 20 kb), group VI strain Y32 (7, 9, 10, and 16 kb), and group XXII strain CT-1 (8 kb). Several of these elements will be characterized and examined for their suitability as spiroplasma cloning vectors.
Insights
This study surveyed extrachromosomal DNA (E-DNA) in spiroplasmas, finding elements in various insect and tick-associated strains. These E-DNA elements show potential as spiroplasma cloning vectors.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Spiroplasmas, helical mollicutes, possess extrachromosomal DNA (E-DNA) in the form of viruses or plasmids.
- These E-DNA elements are being explored as potential vectors for spiroplasma transformation systems.
Purpose of the Study:
- To conduct the first extensive survey of spiroplasma E-DNA across 23 spiroplasma groups (30 strains).
- To identify and characterize E-DNA elements for their potential use as spiroplasma cloning vectors.
Main Methods:
- Improved protocols for E-DNA extraction were utilized.
- A comprehensive survey of E-DNA presence in various spiroplasma groups and strains was performed.
- Hybridization assays were conducted to compare E-DNA elements with known Spiroplasma citri viruses (SpV1, SpV3).
Main Results:
- E-DNA elements were detected in spiroplasmas associated with leafhoppers/plants, other insects, and ticks.
- Elements were often lost after extended passage, suggesting instability.
- Approximately 75% of E-DNA elements from group I spiroplasmas hybridized with SpV1 or SpV3; no hybridization was observed with elements from other spiroplasma groups.
Conclusions:
- This survey provides a foundational understanding of E-DNA distribution in spiroplasmas.
- Several novel E-DNA elements were identified, particularly in non-group I spiroplasmas, warranting further characterization.
- The identified E-DNA elements hold promise for development into functional spiroplasma cloning vectors.