טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentNadel Omer
SubjectUnculture Marine Cyanophages Encode for an Active
Phycobilisome Proteolysis Adaptor NblA Proteins
DepartmentDepartment of Biology
Supervisor Professor Oded Beja
Full Thesis textFull thesis text - English Version


Abstract

Under nutrient limitation, cyanobacteria degrade their phycobilisomes (PBSs), a major lightharvesting complex, allowing the cell to control light energy capture. PBSs are water-soluble membrane-associated complexes in cyanobacteria and red algae that serve as a light-harvesting antenna for the photosynthetic apparatus. PBSs are core complexes of allophycocyanin pigment and peripheral rod pigments. NblA, a small protein (6 kDa), is essential for degradation of PBS and causes a color change from blue-green to yellowish. Cyanobacteria, red algae and some freshwater cyanophages are known to contain nblA gene. A recent study, using assemblies from oceanic metagenomes revealed genomes from a novel uncultured marine cyanophage, which contain genes coding for PBS degradation protein, NblA. Here we examine the functionality of nblA-like genes from this marine cyanophage family by using a Synechococcus elongatus PCC7942 mutant lacking nblA, which does not bleach under nitrogen starvation. We complemented this mutant with a marine cyanophage nblA-like gene and removed nitrogen from the cyanobacterial growth medium in order to examine whether the complemented strain with the nblA gene mutant would restore the wild type phenotype under starvation. Based on previous data and these studies, our findings reveal a functional NblA from a novel marine cyanophage lineage. Additionally, by analyzing genomes of cultured and uncultured marine cyanobacteria and cyanophages, we identified nblA genes that were absent from databases and found that multiplicity of nblA genes per genome is a widespread phenomenon among cyanobacteria. Furthermore, by applying Micro-Raman spectroscopy we demonstrate the existence of a separate PBS disassembly step as part of the NblA-assisted PBS degradation.