Investigating adaptive laboratory evolution strategies to enhance the growth rate and productivity of cyanobacteria
Year: 2026
Type: dissertation
Abstract: Increasing global CO2 emissions, dwindling fossil fuel resources, and environmental damage, collectively present an enormous challenge for our shared future. However, strategies exist to address these challenges. Cyanobacteria are photoautotrophic prokaryotes, capable of fixing carbon and producing a wide range of compounds of commercial interest. These organisms are, however, limited by low growth rates and productivity, when compared to both heterotrophic alternatives, and conventional manufacturing processes. Adaptive laboratory evolution (ALE) was utilised and shown to be an effective strategy for the selection of both unicellular and filamentous cyanobacteria. Following chemostat selection isolates of Synechocystis Δhox showed a 2-fold improvement in biomass accumulation compared to the control and 93.2% of the isolates showed improved biomass formation compared to the control when grown under atmospheric concentrations of CO2. Furthermore, chemostat selection of Trichormus variabilis sp. ATCC 29413 under autotrophic conditions yielded the same increase in biomass. Improvements in biomass accumulation were shown to be as high as 2.7-fold. The fastest growing Synechocystis isolates, Syn.1.11 and Syn.1.19 had an increased μmax following ALE selection. Syn.1.11 showed an increase of 13.5% ±3.6% (standard error) in μmax while Syn.1.19 had an increase of 28% ±17% (standard error) in μmax compared to the control strain Syn.Δhox, when grown in BG-11NH4 and atmospheric CO2. Both strains showed several phenotypic variations from the progenitor strain, including an average 145% ±60% (standard error) increase in rate of peak oxygen evolution in strain Syn.1.11. This despite cells nominally containing on average 16.1% ±22% (standard error) less chlorophyll per mg·DCW-1 than the progenitor strain. Multiple changes were also seen in the genomic DNA including mutations in both the lexA gene, a key regulator in the cell and rppB, a two-component response regulator, which mediates the stoichiometry between the photosystems. Differences were also seen in the metabolite profile of the cells including, an increase in acetylated amino acids, a key posttranslational modification mechanism in the cell and in the metabolites involved in arginine biosynthesis. Following chemostat selection of Trichormus variabilis with fructose supplementation, 3 heterotrophic organisms were also isolated as part of a consortia with the fastest growing strain. This consortium included at least one organism which is capable of nitrogen fixation independent of the cyanobacteria and induced up to ~30% higher growth rates in the wild type when co-inoculated and grown with 1.5% CO2. The fastest growing isolate also showed a decrease in the oxygen evolution rate, despite an improvement in growth, and was more resistant to photoinhibition. The strains isolated in this work demonstrate the power of ALE coupled with continuous selection for identifying potential targets for rational engineering work, and in generating improved strains for commercial exploitation. Furthermore, this work provides novel insights into the use of ALE for selecting photosynthetic prokaryotes with enhanced carbon fixation and biomass formation and may be the first example of ALE used to enhance the productivity of diazotrophic cyanobacteria.
Author: Martin, Christopher
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7217696757