Genomic Changes During Adaptive Evolution to High Oxygen Stress in Synechococcus elongatus PCC 7942

Cyanobacteria in dynamic redox environments must adapt to oxidative stress from diurnal cycles, environmental fluctuations, and nutrient availability. To identify genetic changes underlying improved oxidative stress tolerance and enhanced sucrose production, we performed whole-genome resequencing of S. elongatus PCC 7942 populations experimentally evolved under sustained high oxygen conditions in controlled turbidostatic cultures. Starting from a CscB/SPS-engineered strain, populations were subjected to iterative oxygen stress cycles with increasing oxygen concentrations (0-78.4%, 0-93%, and 0-99.8% oxygen). DNA resequencing revealed mutations in genes associated with molybdopterin biosynthesis and glycogen metabolism that emerged during adaptive evolution. These genomic changes correlated with improved tolerance to elevated oxygen levels and increased sucrose productivity under high-stress conditions. This genomic dataset complements transcriptomic analysis by identifying the genetic basis of evolved stress resistance phenotypes, revealing how multiple rounds of oxidative stress drive adaptive mutations that enhance cellular resilience and metabolic performance.