Molecular insights into the enhanced growth of cyanobacteria by adaptive laboratory evolution in wastewater environments

The expansion of population leads to an increase in nutrient-rich wastewater, posing a threat to the ecosystem. The cultivation of economically beneficial cyanobacteria consumes amounts of freshwater, exacerbating the depletion of freshwater resources. This study investigates the potential of utilizing adaptive laboratory evolution (ALE) to enhance the growth performance of Synechocystis sp. PCC 6803, a model cyanobacterium, in wastewater. After 374 days of ALE, a strain designated as WW was successfully evolved. When cultivated in wastewater, WW exhibited a specific growth rate of 0.317 per day and achieved a dry weight of 0.693 g/L by the 13th day, outperforming the wild type. WW achieved removal efficiencies of 35.55 % for total nitrogen and 60.95 % for total phosphorus in the wastewater. RNA sequencing and photosynthetic measurements revealed that enhanced photosynthetic capacity in the WW contributes to its superior growth performance. The lipid content in WW was 16.19 %, with a notable increase in the proportion of polyunsaturated fatty acids. The shift in fatty acid composition has a consequential impact on biodiesel index, including oxidation stability and saponification number. This study not only demonstrates the effectiveness of ALE in enhancing the growth of cyanobacteria in wastewater for biofuel production, but also offers significant insights into the molecular mechanisms that drive this improved performance.