Viruses, as the most abundant biological entities on Earth, profoundly influence ecosystem material cycles and energy fluxes by hijacking host metabolic pathways. In aquatic ecosystems, cyanobacteria—contributing approximately 20% of global carbon fixation as primary producers—interact with cyanophages, a relationship recognized as pivotal in regulating algal bloom dynamics and carbon-nitrogen-phosphorus cycling. While existing studies predominantly focus on marine systems, significant knowledge gaps persist regarding metabolic interactions between freshwater cyanobacteria and their viruses. This study investigates the metabolic reprogramming effects of viral infection on host fatty acid synthesis using freshwater cyanobacteria and their species-specific cyanophage. Results demonstrate that viral infection induces de novo production of odd-chain fatty acids (OCFAs) in host cells, accompanied by progressive accumulation of both OCFAs and even-chain fatty acids (ECFAs) during infection. Concurrently, elevated reactive oxygen species (ROS) levels were detected. We propose that total fatty acid accumulation may serve as an energy reservoir to fuel viral replication and host-virus metabolic demands, while the distinct structural properties of OCFAs—enhanced antioxidant capacity—likely represent an adaptive host response to mitigate virus-induced oxidative stress. Notably, OCFAs exhibit exceptional stability in geological sediments. Their abnormal accumulation patterns may have great potential as "molecular fossils" to track historical viral infection events in geological records.
 

cyanobacteria, virus, odd-chain fatty acids