Date of Award


Thesis Date


Degree Type

Honors Thesis-Unrestricted

Degree Name



Biological Sciences

Degree Program

Biological Sciences


Wendy Schluchter


Synechococcus, a genus of photosynthetic cyanobacteria, is the second most abundant oxygenic microorganism in the marine environment that contributes significantly to the ocean’s primary productivity (Humily et al. 2013; Shukla et al. 2012). They are capable of utilizing available light of different wavelengths in the visible spectrum to perform photosynthesis and fix carbon dioxide and thus inhabit a wide range of light niches in the ocean along horizontal (coast vs offshore) and vertical gradients (depth) (Humily et al. 2013). A gene encoding a putative lyase isomerase, mpeQ, is present in phycoerythrin-II encoding operon that is expressed constitutively and a gene encoding putative lyase, mpeW, is present in CA-4 genomic island whose expression is regulated by ambient light color were identified and characterized in Synechococcus sp. A15- 62, a strain having a blue light specialist phenotype in its basal state. The amino acid sequence of the proteins encoded by mpeW and mpeQ are similar to other characterized lyases and these genes are conserved in cyanobacteria strains containing the CA4-B genomic island, which controls CA4 (Humily et al. 2013). The MpeW and MpeQ proteins were produced in E. coli and co-expressed with recombinant HT-MpeA and phycoerythrobilin (PEB) synthesis machinery. Site directed mutants of the HT-MpeA protein (Cys75Ala, Cys83Ala, Cys140Ala) were used to investigate the site for bilin attachment. The recombinant protein co-expression experiments of MpeQ and MpeW demonstrated that MpeQ attaches phycoerythrobilin (PEB) to cysteine-83 site on a-phycoerythrin II and isomerizes it to phycourobilin (PUB) and MpeW attaches phycoerythrobilin (PEB) to the same site.


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