Boosting isoprene production via heterologous expression of the Kudzu isoprene synthase gene (kIspS) into Bacillus spp. cell factory

Isoprene represents a key building block for the production of valuable materials such as latex, synthetic rubber or pharmaceutical precursors and serves as basis for advanced biofuel production. To enhance the production of the volatile natural hydrocarbon isoprene, released by plants, animals and bacteria, the Kudzu isoprene synthase (kIspS) gene has been heterologously expressed in Bacillus subtilis DSM 402 and Bacillus licheniformis DSM 13 using the pHT01 vector. As control, the heterologous expression of KIspS in E. coli BL21 (DE3) with the pET28b vector was used. Isoprene production was analyzed using Gas Chromatography Flame Ionization Detector. The highest isoprene production was observed by recombinant B. subtilis harboring the pHT01-kIspS plasmid which produced 1434.3 μg/L (1275 µg/L/OD) isoprene. This is threefold higher than the wild type which produced 388 μg/L (370 μg/L/OD) isoprene, when both incubated at 30 °C for 48 h and induced with 0.1 mM IPTG. Additionally, recombinant B. subtilis produced fivefold higher than the recombinant B. licheniformis, which produced 437.2 μg/L (249 μg/L/OD) isoprene when incubated at 37 °C for 48 h induced with 0.1 mM IPTG. This is the first report of optimized isoprene production in B. licheniformis. However, recombinant B. licheniformis showed less isoprene production. Therefore, recombinant B. subtilis is considered as a versatile host for heterologous production of isoprene.