Leucine-Responsive Regulatory Protein in Acetic Acid Bacteria Is Stable and Functions at a Wide Range of Intracellular pH Levels

Expression of a recombinant protein by an acetic acid bacterial host

We evaluated the suitability of Komagataeibacter europaeus, a vinegar production organism adept at synthetic media growth, as a host for heterologous gene expression. Cryptic plasmids (pGE1 and pGE2 derivatives) from K. europaeus strain KGMA0119 were employed as vectors for heterologous gene expression. The focus was placed on the groES promoter as a potential inducible switch. The groES promoter was fused with the EGFP gene and introduced into a pGE1 derivative to assess its suitability. Ethanol, acetic acid, and heat stresses were examined under various conditions for induction. EGFP transcription surged 600-fold when late logarithmic phase K. europaeus cells, cultured at 30 °C, endured heat stress at 40 °C, coupled with 20% acetic acid and 30% ethanol stress after an additional 6-hour cultivation. This robust induction system was then applied to express two proteins, Tth pol from the thermophilic bacterium Thermus thermophilus strain M1 and UPV230, a restriction enzyme from the acid-tolerant microorganism Ureaplasma parvum, known to cause vaginal infections and miscarriages. Both Tth pol and UPV230 were successfully expressed in K. europaeus cells and purified. The recovery of Tth pol from K. europaeus cells (480 µg protein per liter culture) was approximately half that from E. coli (960 µg protein per liter culture). In contrast, UPV230 recovery from K. europaeus cells (640 µg protein per liter culture) was nearly 10 times higher than that from Escherichia coli (66 µg protein per liter). The data highlights the potential of acetic acid bacteria as a host for producing acidophilic proteins. The shift in recognition from a 6-base sequence to a 4-base sequence of UPV230 was observed, accompanied by a change in structure as the pH transitioned from acidic pH to near-neutral pH.