The influence of medium composition on the microbial secretory production of hydroxyalkanoate oligomers

Abstract

With the aid of a chain transfer (CT) reaction, hydroxyalkanoate (HA) oligomers can be secreted by recombinant Escherichia coli carrying the gene encodi ng a l act at e-pol ymeri zi ng enzyme (PhaC1Ps STQK) in Luria-Bertani (LB) medium supplemented with a carbon source and CT agent. In this study, HA oligomers were produced through microbial secretion using a mineral-based medium instead of LB medium, and the impact of medium composition on HA oligomer secretion was investi-gated. The focused targets were medium composition and NaCl concentration related to osmotic conditions. It was observed that 4.21 g/L HA oligomer was secreted by recombinant E. coli in LB medium, but the amount secreted in the mineral-based modi-fied R (MR) medium was negligible. However, when the MR medium was supplemented with 5 g/L yeast extract, 3.75 g/L HA oligomer was secreted. This can be accounted for by the enhanced expression and activity of PhaC1Ps STQK upon supplementation with growth-activated nutrients as supplemen-tation with yeast extract also promoted cell growth and intracellular growth-associated polymer accu-mulation. Furthermore, upon adding 10 g/L NaCl to the yeast extract-supplemented MR medium, HA oligomer secretion increased to 6.86 g/L, implying that NaCl-induced osmotic pressure promotes HA oligomer secretion. These findings may facilitate the secretory production of HA oligomers using an inexpensive medium.