Prof. Rakefet Schwarz

Our laboratory employs genetic approaches and cutting-edge molecular tools to study mechanisms allowing cyanobacteria to sense changes in the environment and survive under a large variety of conditions. Cyanobacteria had, and still have a substantial impact on life on earth. Being the first organisms that performed ‘oxygenic photosynthesis’, cyanobacteria had a pivotal role in the history of life by changing the chemistry of the atmosphere and allowing the development of aerobic eukaryotes. Furthermore, cyanobacteria are considered the ancestors of chloroplasts of algae and higher plants. Currently, the central ecological importance of cyanobacteria is manifested in their significant contribution to global CO₂ fixation (25-30% of global CO₂ fixation is attributed to cyanobacteria). Additional major environmental impact stems from cyanobacterial blooms, which affect the entire food chain, and in cases of ‘toxic blooms’ cause the collapse of large aquatic ecosystems and impact the quality of water reservoirs. Our studies of cyanobacterial stress physiology and the molecular mechanisms underlying it, provide insight into fundamental cellular processes, e.g. regulated proteolysis and multicellular behavior of bacteria.

Cyanobacterial Biofilms

Biofilms are bacterial communities encased by extracellular matrix produced by the residing bacteria. Cyanobacterial biofilms are environmentally prevalent, and additionally, often occur in an industrial context, imposing damage and leading to financial loss; however, information on cyanobacterial mechanisms involved in biofilm development is scarce. Thus, our studies provide a new cellular context in which to investigate the developmental process of biofilm formation. We recently uncovered a process of self-inhibition of biofilm formation in the cyanobacterium S. elongatus. Additionally, we identified genes essential for biofilm development.

Regulated Proteolysis of the Phycobilisome

Cyanobacteria, much like other photosynthetic organisms, adjust their light harvesting apparatus in response to environmental cues. This tuning allows effective light absorbance for the phototrophic metabolism while preventing the deleterious effect of surplus excitation. The phycobilisome, the cyanobacterial pigment antenna, is a supramolecular assembly that may reach 4 MDa. A small protein, NblA, is essential for the degradation of this pigment complex under nutrient limitation. We recently revealed that this small protein associates with phycobilisomes attached to the photosynthetic membranes. We propose that NblA serves a dual function: undermining complex stability and designating the dissociated pigments for degradation.

Tailoring Cyanobacteria for Biofuel

Environmental as well as economic factors call for sustainable alternatives to the use of fossil fuels. Biofuels derived from arable crops are not cost-effective and the impact of these ‘first generation biofuels’ on food supply and price have raised ethical questions. Photosynthetic microorganisms offer an efficient means for biofuel production that is not associated with the current problems of land-based feedstock. We genetically modified S. elongatus in order to increase accumulation of glycogen, a raw material for bioethanol production.