Date of Award

8-2013

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Microbiology

Advisor

Lisa R. Moore

Second Committee Member

Mary Jane Perry

Third Committee Member

Mary Rumpho

Abstract

The marine cyanobacteria Prochlorococcus and Synechococcus are the most abundant phototrophs in the oceans. They cohabit the oligotrophic ocean and thus have coevolved together, yet they have distinctly different methods for harvesting light. Synechococcus, like other cyanobacteria, possess phycobilisomes with various combinations of phycobiliproteins to capture wavelengths of light not otherwise available to chlorophyll. Prochlorococcus lack phycobilisomes and use divinyl chlorophyll b (Chl b2) as their primary accessory pigment to divinyl chlorophyll a (Chl a2) to capture light energy. In addition to the divinyl chlorophylls, Prochlorococcus has genes associated with the phycobiliprotein phycoerythrin (PE), the role of which is still not fully understood, though it is unlikely to contribute significantly to photosynthesis. Past studies have focused on characterizing PE expression on a few isolates of Prochlorococcus, the Low Light adapted (LL) II/III ecotype SS120, High Light (HLI) ecotype MED4 and HLII ecotype AS9601. These studies found that the LLII/III SS120 ecotype expressed both PE chromophores, phycoerythrobilin (PEB) and phycourobilin (PUB), whereas the HL ecotypes only expressed PEB. However, the LL ecotypes have more extensive phylogenetic diversity, so I sought to characterize the diversity in PE physiology for Prochlorococcus isolates from three LL ecotypes using a combination of flow cytometry, spectrofluorometry, and pigment measurements. I confirmed that the flow cytometric orange fluorescence (FL2) signal was due to PE in all LL Prochlorococcus strains examined and found differences in phycobilin composition among the LL Prochlorococcus strains. For instance, some LLIV ecotype strains did not have measurable PEB and most strains increased their PE expression per cell when grown at low light irradiances, suggesting PE is photoacclimating in LL Prochlorococcus. The physiological differences observed for LL Prochlorococcus strains and ecotypes highlight the necessity of examining more than one strain from an ecotype to make inferences about ecotypic physiology.

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