Optimization of Growth Conditions for the Model Bacterium Synechococcus sp. PCC 7002 for Chemical Production Using Wastewater-Based Media

Abstract

The term “cyanobacterial biorefinery” refers to the application of genetically engineered cyanobacteria for production of chemicals that could serve as an alternative source to petroleum derivatives. Various life cycle assessments have indicated that nutrient sources for cell cultivation are a major limitation of the cyanobacterial biorefinery concept from both cost and environmental impact perspectives. Wastewater streams have previously been identified as possible promising sources of liquid macronutrients, but little work has investigated their use for axenic cyanobacterial culture. In these experiments, we grew the model cyanobacterium Synechococcus sp. PCC 7002 in media comprised of two municipal wastewater streams: anaerobic digester effluent (“GBF”) and secondary treatment clarifier effluent. Temperature, light intensity, and media composition effects on cytotoxicity and growth rate were investigated in two engineered strains of Synechococcus 7002. At 27°C, we were able to ameliorate most of the toxicity and growth inhibition observed in cells grown at high GBF concentration and 37°C, the latter which is considered optimal temperature for growth in minimal media. We also found significant interaction between factors, which indicates the importance of co-optimization of environmental conditions and suggests several possible causal mechanisms. This work represents an important first step towards developing sustainable alternatives for resource recovery from wastewater while reducing dependence on petroleum feedstocks for chemical production.