DEVELOPING ALTERNATIVE SOURCES OF FEEDSTOCKS FOR INDUSTRIAL HYDROCARBONS: OPTIMISATION OF BIOMASS AND STRESS-INDUCED LIPID PRODUCTION IN Synechocystis SR

Abstract

Hydrocarbons from fossil fuels play a key role in supporting diverse socio-economic activities and growth of the global economy. Principally, hydrocarbons are used as fuels for energy generation and as raw materials for manufacturing products of high economic value, such as lubricants, packaging material, and agrochemicals. Due to greenhouse gas emissions associated with use of fossil fuel products, alternative sources of feedstocks to manufacture industrial hydrocarbons are highly sought after. This project explored the utility of a newly discovered cyanobacterial strain (Synechocystis SR) as a source of lipids for industrial applications. In experiments to optimise biomass production, a two-stage system sequencing 5 days of high light (150 μmol.m-2.s-1) followed by 2 days of low light (75 μmol.m-2.s-1) incubation of cyanobacterial cultures produced the best growth results. Because lipid production in cyanobacteria is activated by stress, the impact of NaCl and the mycotoxin fumonisin B1 (FB1) on growth was evaluated. FB1 exhibited no growth inhibitory activity against neither Synechocystis SR nor the control strain Synechocystis PCC 6803. However, salinity stress imposed by NaCl had a disproportionately higher impact on the growth of Synechocystis PCC 6803 than Synechocystis SR. The effects of salinity on cyanobacterial growth were dependent on light, with high light totally inhibiting growth while low light incubation followed by high light enabled the cultures to acclimate and survive the stress. Salinity stress activated expression of all the fatty acid biosynthetic pathway genes, with Synechocystis SR showing higher gene expression than Synechocystis PCC 6803. The activation in gene expression led to a two-fold increase in total lipid accumulation in Synechocystis SR. Even though there was an increase in the amount of total lipid, the profile of fatty acid methyl esters (FAMEs) remained unchanged. FAMEs extracted from Synechocystis SR could be used as an industrial feedstock for production of diverse industrial hydrocarbon products.