Salinity effect on production of PHA and EPS by Haloferax mediterranei

The halophilic archaeon, Haloferax mediterranei, is able to produce polyhydroxyalkanoates (PHAs) in large quantities. Along with the synthesis of PHAs by H. mediterranei, an extracellular polymeric substance (EPS) is excreted as a byproduct, lowering the efficiency of the production of PHAs. In this experiment, salinity effects on the carbon distribution to synthesis of PHAs and/or EPS were explored in order to control their production. It was found that high NaCl concentrations inhibited the productivity of EPS while encouraging the productivity of PHAs. The optimal salinity for the growth and proliferation of H. mediterranei was in the range of 150-200 g L-1. EPS productivity decreased from 371.36 to 319.74 mg EPS per g CDW as the concentration of NaCl increased from 75 g L-1 to 250 g L-1. However, high salinity promoted the synthesis of PHAs. When the NaCl concentration was 250 g L-1, the intracellular content of PHAs reached a maximum of 71.1%. This result indicated that a high NaCl concentration significantly stimulated the production of PHAs while depressing the production of EPS. This study provided a possible solution to adjust the carbon distribution to the synthesis of PHAs and EPS by H. mediterranei by controlling the concentration of NaCl.