Systems Biology of a diazotrophic unicellular cyanobacterium of the genus Cyanothece
Prof. Louis Sherman
West Lafayette, Indiana USA
The goal of engineering cyanobacteria to produce of high-value compounds, like biofuels, comes with many challenges. Physiological characteristics such as growth rate, culture heterogeneity, and nutrient storage can impact the facility of using specific organisms for targeted chemical production. In addition, an increasing body of evidence suggests that post-transcriptional regulatory mechanisms are prevalent in cyanobacteria. The unicellular genus Cyanothece consists of diazotrophic cyanobacteria that can fix atmospheric N2 in addition to CO2. Cyanothece strain PCC 7822 is the only member of this genus that is amenable to genetic modification. This strain stores a significant amount of nutrients in intracellular granules, extrudes exopolysacchrides making macromolecule isolation difficult and cells to aggregate. Also, little is known about the expression dynamics of metabolic pathways that could be used for biofuel production. In order to further develop this strain for the industrial purposes, an integrated approach was applied consisting of three main areas; physiology – how cells grow and store carbohydrates under different conditions; gene expression – utilizing transcriptomics and proteomics to understand how different metabolic reactions occur within the cell; and genetics – monitoring the effects of different genetic modifications in order to generate novel metabolic capabilities.
Nitrate and phosphate levels in BG-11 growth media were reduced and flow cytometry and transmission electron microscopy were used to determine the effects on various physiological properties. Reducing these nutrient concentrations led to a decrease
in intracellular storage, improved the growth rate, and increased culture homogeneity. Global metabolic dynamics were quantitated during standard growth conditions at four time points across a 24 hour light-dark cycle through a parallel transcriptomics and proteomics investigation. This is the first time such a study has been described for Cyanothece 7822. In addition, glycogen biosynthesis mutants were generated to study the enzymatic basis for variation in carbohydrate storage among cyanobacterial species and to test whether or not altering the structure of stored sugar granules can influence the production of downstream compound.