CHARACTERIZATION OF THE FaRLiP PHYCOBILIPROTEIN COMPLEX BY DELETION MUTAGENESIS IN THE CYANOBACTERIUM SYNECHOCOCCUS SP. PCC 7335

Open Access
Author:
Turner, Gavin M
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Donald Ashley Bryant, Thesis Supervisor
  • Ronald Albert Markle, Honors Advisor
Keywords:
  • FaRLiP
  • Cyanobacteria
  • Phycobilisome
  • Synechococcus sp. PCC 7335
Abstract:
In far-red light (FRL) conditions, the cyanobacterium Synechococcus sp. PCC 7335 produces FRL-phycobiliprotein (PBP) complexes composed of seven different protein subunits. Five of these subunits are paralogous copies of the PBS core protein, allophycocyanin (AP). These APs are uniquely expressed in FRL and are encoded by their corresponding genes (apcB2, apcD2, apcD3, apcD5, apcE2). These five genes were mutated individually via deletion mutagenesis and replaced by the aphA2 gene, conferring kanamycin resistance. The resulting mutant strains lacking the deleted AP proteins produced distinct phenotypes. These mutants were characterized by absorbance and low-temperature fluorescence emission spectroscopy of whole cells when grown in white light (WL) and FRL conditions. Compared to wild-type cells, mutants exhibited a deficiency in assembly and energy transfer through their FRL-PBP complexes, indicating reduced or eliminated FRL-PBP assembly. In addition, the mutants showed much lower concentrations of chlorophyll d and chlorophyll f (Chl d and Chl f) compared to wild-type cells. This deficiency is consistent with the hypothesis that the cysteine-rich FRL-PBPs may play a role in Chl d synthesis.