Abstract
Microalgae are photosynthetic organisms that possess considerable potential for pigment production as natural colourants for applications in the food industry, feed, cosmetics, nutraceuticals, and related sectors. However, their biological function is inseparable from stress physiology, excitation control, and redox balance, and current commercial production of natural microalgal pigments remains insufficient to meet growing market demand. A central limitation is the recurrent growth-pigment trade-off: environmental conditions that stimulate pigment accumulation often suppress biomass formation while growth-favourable regimes dilute secondary pigment pools. Adaptive laboratory evolution and long-term experimental evolution provide a conceptual bridge between ecological adaptation and engineering design by demonstrating that stable pigment phenotypes typically emerge from selection acting on excitation pressure, redox homeostasis, and membrane organisation rather than from direct selection on pigment flux alone. These findings reframe pigment overproduction as a consequence of relieving upstream physiological constraints. We advance a systems-based framework where microalgal pigments are treated as programmable, stress-responsive modules embedded within integrated photosynthetic and metabolic networks. Focusing on astaxanthin, phycocyanin, and scytonemin as representative architectures, we synthesise advances in clustered regularly interspaced short palindromic repeats (CRISPR)-mediated genome editing, synthetic promoter engineering, metabolic pathway refactoring, and systems biology modelling that enable stabilisation of stress-resilient phenotypes.