To salt or not to salt: Optimized production and sequential downstream processing of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and bacterioruberin from Haloferax mediterranei

This study presents an integrated bioprocess for the sustainable production and simultaneous recovery of two high-value bioproducts – poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and bacterioruberin (BR) – from the halophilic archaeon Haloferax mediterranei. A Response Surface Methodology was applied to optimize key fermentation parameters, such as NaCl concentration, carbon-to-nitrogen (C/N) ratio, and nitrogen source. Both minimal synthetic medium and seawater were assessed, the latter demonstrating potential as a more sustainable alternative to freshwater-based cultivation systems. Optimal PHBV accumulation (25 % gpolymer/gCDW) was achieved under high salinity (167.7 g L−1 NaCl), a C/N ratio of 40, and with KNO3 as the nitrogen source. In contrast, BR production was maximized (7.8 mg L-1) under moderate salinity (100 g L−1) and a lower C/N ratio (8). To enable efficient product separation, a sequential downstream strategy was developed, allowing recovery yields of PHBV and BR comparable to conventional single-product extraction protocols, while reducing reliance on halogenated solvents. Overall, the proposed process supports the valorization of halophilic biomass through a resource-efficient platform, contributing to the development of integrated biorefinery approaches aligned with principles of green and sustainable chemistry.