Date of Award


Document Type


Degree Name

Master of Science (MS)


College of Science and Mathematics



Thesis Sponsor/Dissertation Chair/Project Chair

Lee H. Lee

Committee Member

Quinn C. Vega

Committee Member

John Gaynor


Synechococcus sp. IU 625 (Anacystis nidulans) is a freshwater unicellular cyanobacterium and an obligate photoautotroph that readily harbors plasmids. This organism has been used in many studies to assess the effect of heavy metal toxicity as an environmental pollutant. In one of the few studies for strain IU 625, Simon isolated 4.7- MDa and 37-MDa plasmids in 1978. The relationship between these plasmids and the 7.6-kb and 46.6-kb plasmids of strain PCC 7942 is unknown. Primers designed based on the sequence of 46.6-kb plasmid pANL of PCC 7942 exhibited positive priming with isolated plasmid DNA from Syn. sp. IU 625. Sequence analysis showed high homology with the respective sequences in plasmid pANL.

Cyanobacteria like Syn. sp. IU 625 have general metal resistance mechanisms. However, tolerance to mercury, the heavy metal with the strongest toxicity, is dependent on mercury resistance determinants (mer) that are commonly found in plasmids. Research into the genome of related strain PCC 7942 indicates that mer genes may also be located on the genome. The present study addresses the issue of plasmid versus chromosomal mediated mercury tolerance in Syn. sp. IU 625. Priming of pure genomic DNA from IU 625 cells with plasmid-specific and chromosomal-specific primers for mercury resistance showed positive priming with only chromosomal specific primers. Priming of isolated plasmid DNA from IU 625 with the same primers showed positive priming with only the plasmid-specific primers. Therefore, the findings suggest that mer determinants are located on both plasmid and genome. Preliminary findings from studying the induction of the plasmid in IU 625 in response to mercury stress suggest that the plasmid is induced early on after the introduction of the heavy metal.

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