Co-production of polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPSs) by halophilic archaeon Haloferax mucosum†

Abstract

This is the first report on the co-production of polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPSs) by the halophilic archaeon Haloferax mucosum (DSM 27191) in a modified ATCC 2185 medium (NaCl 2.5 M, yeast extract 6 g L⁻¹) with nitrogen limitation (C/N = 35 molar ratio), where it can produce 6.7 g_EPS L⁻¹ and 0.25 g_PHA L⁻¹. The PHA production is favoured when NaCl increases to 4 M and at higher nitrogen limitation (C/N = 50) reaches 0.75 g_PHA L⁻¹, but the EPSs were not detectable in the supernatant. The recovered PHAs are a copolymer of P(3HB-co-3HV), and the production conditions impact their chemical features (i.e. 3HV content, melting temperature, degree of crystallinity and molar mass). EPSs are anionic sulfated heteropolysaccharides composed of uronic acids, glucose, galactose, mannose and fructose. Purified EPSs have a high molar mass of 901 kDa and exhibit shear-thinning rheological behaviour in aqueous solution.