Expression of an engineered salt-inducible proline biosynthetic operon in a Glutamic acid Over-Producing mutant, Halomonas elongata GOP, confers increased proline yield due to enhanced growth under high-salinity conditions.

L-Proline (Pro) is an essential amino acid additive in livestock and aquaculture feeds. Previously, we created a Pro overproducing Halomonas elongata HN6 by introducing an engineered salt-inducible Pro biosynthetic mCherry-proBm1AC operon and deleting a putA gene that encoded a Pro catabolic enzyme in the genome of H. elongata OUT30018. Here, we report a generation of a novel Pro overproducing H. elongata HN10 strain with improved salt tolerance and higher Pro yield by expressing the mCherry-proBm1AC operon and deleting the putA gene in the genome of a spontaneous mutant H. elongata GOP, which overproduces glutamic acid (Glu) that is a precursor for Pro biosynthesis. The optimal salt concentration for growth of H. elongata HN10 was found to be 7% to 8% w/v NaCl, and the average Pro yield of 166 mg/L was achieved when H. elongata HN10 was cultivated in M63 minimal medium containing 4% w/v glucose and 8% w/v NaCl.