Polyhydroxyalkanoate Production Under Saline Conditions: A Review of Pure and Mixed Microbial Culture Systems

Polyhydroxyalkanoates (PHAs) are promising biodegradable and bio-based alternatives to conventional plastics; however, their industrial implementation remains challenged by high production costs, refined carbon sources, stringent cultivation requirements, and energy-intensive downstream processing. Saline bioprocessing offers an emerging strategy to address these limitations by exploiting the robustness of halophilic and halotolerant microorganisms and valorizing saline, low-cost, and waste-derived feedstocks. This review provides a critical analysis of PHA production under saline conditions, focusing on halophilic and halotolerant pure cultures and saline mixed microbial cultures (MMCs). The bioprocess chain is examined, encompassing feedstock selection and pretreatment, microbial adaptation, cultivation and enrichment, process optimization, metabolic and genome engineering, and PHA recovery and purification. Particular attention is given to physiological responses to salinity and their effects on growth, carbon allocation, PHA accumulation, and polymer composition. Pure cultures and MMCs are compared in terms of substrate flexibility, process robustness, productivity, polymer properties, scalability, and downstream requirements. Emerging strategies, including waste valorization, saline resource integration, community engineering, process control, and salt recovery, are discussed. Finally, knowledge gaps and technological bottlenecks are identified to guide the development of viable and sustainable saline PHA bioprocesses.