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Transcriptional Response and Adaptive Evolution to Oxidative Stress in Synechococcus elongatus PCC 7942

ABSTRACT: Cyanobacteria inhabit dynamic redox environments influenced by diurnal cycles, environmental fluctuations, and nutrient availability, necessitating tight redox regulation. This RNA-seq study examines transcriptional regulation of redox control in the model cyanobacterium Synechococcus elongatus PCC 7942 under controlled turbidostatic conditions. We manipulated oxygen concentrations to generate oxidative stress across distinct phases, measuring impacts on growth, physiology, and genome-wide gene expression. Transcriptional profiling reveals independently regulated gene modules that define graded transcriptional responses aligned with redox-regulated patterns activated under fluctuating light conditions. Our findings demonstrate a coordinated, multi-phase response involving ROS formation, detoxification, and damage repair. Oxidative stress induces transcriptional repression of essential cellular processes. This dataset includes wild-type strains under acute oxidative stress and experimentally evolved populations that underwent multiple rounds of elevated oxygen exposure. The evolved strains demonstrated improved tolerance to elevated oxygen levels, enhanced sucrose productivity under high-stress conditions, and accumulated DNA mutations in genes related to molybdopterin biosynthesis and glycogen metabolism.

ORGANISM(S): Synechococcus elongatus PCC 7942 = FACHB-805

PROVIDER: GSE311172 | GEO | 2025/11/26

REPOSITORIES: GEO

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Project description:The industrial feasibility of photosynthetic bioproduction using cyanobacterial platforms remains challenging due to insufficient yields, particularly due to competition between product formation and cellular carbon demands. Here we demonstrate that circadian regulation impacts carbon partitioning between storage, growth, and product synthesis in Synechococcus elongatus PCC 7942, significantly affecting production efficiency. After entrainment to light-dark cycles, cultures maintained under the constant light revealed distinct temporal patterns in sucrose production, exhibiting three-fold higher productivity during subjective night despite moderate down-regulation of the photosynthetic apparatus. This enhanced productivity coincided with reduced glycogen accumulation and halted cell division, suggesting temporal separation of competing processes. Transcriptome analysis revealed coordinated circadian-driven adjustment of the cell cycle and rewiring of energy and carbon metabolism. The subjective night was characterized by altered expression of cell division-related genes and reduced expression of genes involved in glycogen synthesis, while showing upregulation of glycogen degradation pathways, alternative electron flow components, the pentose phosphate pathway, and oxidative decarboxylation of pyruvate. These molecular changes created favorable conditions for product formation through enhanced availability of major sucrose precursors (glucose-1-phosphate and fructose-6-phosphate) and maintained redox balance. Our findings suggest that understanding the circadian regulatory rewiring of carbon metabolism could enable two distinct approaches for improving cyanobacterial bioproduction. First, accounting and leveraging natural circadian rhythms for optimizing cultivation conditions, timing of heterologous pathway induction and harvesting patterns. Second, engineering strains that mimic circadian-driven metabolic shifts through controlled carbon flux redistribution and redox rebalancing to enable efficient cycling between growth, storage accumulation, and production phases.

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Transcriptional Response and Adaptive Evolution to Oxidative Stress in Synechococcus elongatus PCC 7942

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