Research: Project 3

Cell-specific gene expression and metabolic flux analysis in Anabaena variabilis. Filamentous heterocyst-bearing cyanobacteria are unique forms of multicellular bacteria, in which two different cell types simultaneously perform complementary metabolic functions?oxygenic photosynthesis in vegetative cells and N2 fixation in heterocysts. Cyanobacteria are receiving serious attention as possible catalysts for the production of H2, biofuels, and other bioproducts. Filamentous cyanobacteria have been predicted to have at least a 100-fold higher capacity to produce H2 than unicellular cyanobacteria. The metabolism of filamentous heterocyst-bearing cyanobacteria?especially that of heterocysts?remains poorly characterized. Our main objective is to fill this knowledge gap by identifying which small molecules are transported between vegetative cells and heterocysts, how the two cell types are metabolically interdependent, and which metabolic pathways produce the reducing equivalents needed for N2 fixation and H2 production.

A. variabilis is amenable to MFA using 13C-labeled fructose as the carbon source. Our goal is to quantify metabolic fluxes, including intercellular fluxes, in mixotrophically grown, N2-fixing A. variabilis filaments. Knowing the carbon metabolic fluxes should enable us to identify the main pathways that provide reductant for N2 fixation and H2 evolution. By contributing an exact blueprint of intracellular metabolism and intercellular transport in heterocyst-bearing cyanobacterial filaments, our project will help us understand how the two cell types can perform complementary functions. Our results should open the field to many more research endeavors delving into the fascinating biology of these bacteria.