Engineering Halomonas for low-salt, open, and unsterile production of polyhydroxybutyrate

Halophiles enable convenient open, unsterile cultivation, but excessive salinity causes downstream burdens. This study engineered Halomonas bluephagenesis via genome editing, adaptive evolution, and metabolic rewiring to create a series of super low-salinity-adapted halophiles with robust growth in as low as 0.1% w/v NaCl salinity and alkaline pH 9 circumstances while preserving high-salinity resilience, significantly broadening osmotic tolerance for open, unsterile growth with contamination resistance. Multiomics and phenotypic analyses suggest mechanisms of the broad salinity-adaptive halophiles reflected in changing surface properties, enlarged morphology, auto-flocculation, and broader bioproduct synthesis. The optimized strain supported stable 7 l bioreactor cultivation at 5 g/l NaCl to reach 76 g/l cell dry weight containing up to 86% polyhydroxybutyrate (PHB) with a 39% glucose-to-PHB yield within 44 h of contamination-free growth under open, unsterile conditions, demonstrating the value of Halomonas for flexible industrial applications without high salinity concerns.