Plasmids in diatom species

Abstract

We have discovered plasmids in 5 of 18 diatom species surveyed. In several species, more than one type of plasmid is present. Several of the plasmids show similarity by hybridization to previously characterized plasmids in Cylindrothecafusiformis (J. D. Jacobs et al., unpublished data). Additionally, there is similarity between the plasmids found in C. fusiformis and chloroplast DNA in three diatom species. These results add to the evidence that the plasmids have features of mobile genetic elements.We have recently discovered two small circular DNA plasmids, pCfl and pCf2, in the marine diatom Cylindrotheca fusiformis (9). These plasmids are 4.27 kbp (pCfl) and 4.08 kbp (pCf2) in size. Sequence analysis (8) shows that the plasmids share a large region of significant similarity. They hybridize to each other under low-stringency conditions but not under high-stringency conditions. Under high-stringency conditions, both plasmids hybridize to high-molecularweight (genomic) chloroplast DNA, and pCf2 also hybridizes to nuclear DNA. When coupled with the sequence information, this suggests that substantial portions of the plasmids are present in genomic DNA. The evidence to date is consistent with the hypothesis that the plasmids are mobile genetic elements (8). These intriguing results prompted us to see whether plasmids commonly occur in other diatom species and to determine whether they share similar features.

The Complete Plastid Genomes of the Two ‘Dinotoms’ Durinskia baltica and Kryptoperidinium foliaceum

“…If they were in the ancestor of the tertiary endosymbionts then D. baltica would have to have ridded itself of all evidence of both plasmids to revert to a highly similar form as P. tricornutum . Both explanations, the multiple movements of plasmids between close relatives or the complete loss of plasmids in certain lineages, are consistent with the seemingly sporadic interspecies and intraspecies distribution of these plasmids in diatoms: only 5 out of 18 examined diatom species and only 1 out of 3 strains of the pennate diatom C. closterium are suggested to have similar plasmids [54]. Perhaps the most likely explanation is that the ancestor possessed unintegrated plasmids and a plastid genome with a structure highly similar to that of P. tricornutum and D. baltica .…”

ALGAL TRANSGENICS IN THE GENOMIC ERA1

“…One could also imagine that the small DNA plasmids that are widespread among the Rhodophyta (Moon and Goff 1997) could be engineered for high copy number transgene expression in various species of red algae. Plasmids have also been found in the chloroplasts of various diatoms and marine green algae (Hildebrand et al 1991, La Claire II and Wang 2000) and could be exploited for chloroplast transformation of these species, as could the DNA minicircles that comprise the chloroplast genome of peridinin‐containing dinoflagellates (Koumandou et al 2004).…”

Nucleotide sequence of diatom plasmids: identification of open reading frames with similarity to site-specific recombinases

“…This facilitates proper partitioning of plasmids to daughter cells [5]. Other site-specific recombination systems play similar roles in bacterial plasmid maintenance [2, 14, 381. We have discovered plasmids in a number of diatom species [21]. Two plasmids, pCfl and pCf2, from the marine diatom Cylindrotheca fusiformis have been characterized in detail.…”