Enhanced recombinant protein production in pyruvate kinase mutant of Bacillus subtilis

Using small molecules as a new challenge to redirect metabolic pathway

The presence of acetate in the bacterial medium leads to a reduction in the growth rate of cells and recombinant protein production. In this study, three compounds including propionic acid, lithium chloride and butyric acid were added to the medium which decreased acetate levels and enhanced recombinant protein production (alpha-synuclein). In fact, propionic acid and lithium chloride are both known as acetate kinase inhibitors. The results obtained in the case of butyric acid were similar to those of the two other compounds indicating that butyric acid may act through a mechanism similar to propionic acid and lithium chloride. Consequently, it was shown that the presence of each of these supplements (5–200 μM) increased recombinant alpha-synuclein production and cell density by approximately 10–15 %. HPLC analysis showed that the levels of acetate in the media containing the supplements were considerably less than those of the control. Furthermore, pH values remained almost constant in the supplemented cultures. Growing the bacteria at lower temperatures (25 °C) indicated that the positive effects of these supplements were not as effective as at higher temperatures (37 °C), presumably due to the adequate balance between oxygen and carbon consumption. This study can confirm the viewpoint regarding the harmful effects of acetate on the recombinant protein production and cell density. Besides, such methods represent easy and complementary ways to increase target recombinant protein production without negatively affecting host cell density, and requiring complex genetic manipulation.