Heterologous expression of carbonic anhydrase in <i>Acinetobacter</i> sp. Tol 5 for whole-cell biocatalysis

Carbonic anhydrase accelerates the hydration of carbon dioxide (CO₂) and is an attractive biocatalyst for carbon capture and utilization. Acinetobacter sp. Tol 5 shows high adhesiveness via its cell-surface protein AtaA. We previously demonstrated its application to bacterial immobilization and gas-phase bioproduction. Here, we developed Tol 5 cells expressing carbonic anhydrase and evaluated CO₂ conversion ability as whole-cell biocatalysts. A codon-optimized carbonic anhydrase from Sulfurihydrogenibium yellowstonense (SyCA) was produced in the cytoplasm, but the cells showed little activity as a whole-cell biocatalyst. To enhance activity, we fused six signal peptides (SPs) to SyCA for periplasmic expression. The Omp38-SP fusion of SyCA was properly processed to the mature size, yielding higher whole-cell activity. By contrast, the other constructs were either undetectable or remained unprocessed, resulting in lower activities. These results show that periplasmic expression of SyCA is important for efficient CO₂ hydration in Tol 5 cells as whole-cell biocatalysts.