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Structure and replication of cryptic plasmids, pMA1 and pMA2, from a unicellular cyanobacterium, Microcystis
H Tominaga1, S Kawagishi, H Ashida
1Laboratory of Applied Biologicial Science, Faculty of Agriculture, Shimane University, Japan.
Abstract:
The 4993-bp cryptic plasmid, pMA2, from a cyanobacterium, Microcystis aeruginosa f. aeruginosa Kützing, originally derived from Kasumigaura lake, was completely sequenced and analyzed. Plasmid pMA2 had a unique sequence motif CTTGATT, which was proposed to be a nicking site on the smaller plasmid pMA1 (2287-bp) by the presence of single-stranded DNA susceptible to S1 nuclease. We had detected the occurrence of the single-stranded pMA1 in the living M. aeruginosa cells. This was also the case of pMA2. Thus, we suggest that both plasmids, pMA1 and pMA2, replicate through the rolling circle mechanism. By computer analysis of the pMA2 sequence, two open reading frames were found: one had a predicted molecular size of 30,440 Da and the other on a complementary one had a predicted molecular size of 10,852 Da. No rep protein was detected. Replication mechanisms of the plasmids are discussed.
Insights
Researchers sequenced the Microcystis aeruginosa cryptic plasmid pMA2. Both pMA1 and pMA2 likely replicate via rolling circle mechanism, evidenced by single-stranded DNA in cells.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Cryptic plasmids are extrachromosomal DNA elements found in bacteria.
- Microcystis aeruginosa is a cyanobacterium known to produce toxins.
- Understanding plasmid replication is crucial for microbial genetics.
Purpose of the Study:
- To completely sequence and analyze the cryptic plasmid pMA2 from Microcystis aeruginosa.
- To investigate the replication mechanism of plasmids pMA1 and pMA2.
- To identify potential open reading frames and functional elements within pMA2.
Main Methods:
- Complete DNA sequencing of the 4993-bp plasmid pMA2.
- Bioinformatic analysis of the pMA2 sequence, including open reading frame identification.
- Detection of single-stranded DNA in living M. aeruginosa cells using S1 nuclease susceptibility.
Main Results:
- The complete sequence of the 4993-bp cryptic plasmid pMA2 was determined.
- A unique sequence motif (CTTGATT) potentially acting as a nicking site was identified.
- Single-stranded forms of both pMA1 and pMA2 were detected in M. aeruginosa cells.
- Two open reading frames were identified in pMA2, with predicted molecular sizes of 30,440 Da and 10,852 Da.
- No rep protein was detected in the analyzed sequence.
Conclusions:
- The presence of single-stranded DNA suggests that both pMA1 and pMA2 plasmids replicate via the rolling circle mechanism.
- The identified sequence motif may play a role in plasmid replication initiation.
- Further studies are needed to elucidate the precise replication mechanisms and functions of these cryptic plasmids.