초록
Recently, a bubbleless membrane bioreactor (BMBR) has been successfully developed for biosurfactant production by Bacillus subtilis[1]. In this study, for the first time, continuous culture were carried out for the production of surfactin in a BMBR, both with or without a coupled microfiltration membrane. Results from continuous culture showed that a significant part of biomass was immobilized onto the air/liquid membrane contactor. Immobilized biomass activity onto the air/liquid membrane contactor was monitored using a respirometric analysis. Kinetics of growth, surfactin and primary metabolites production were investigated. Planktonic biomass, immobilized biomass and surfactin production and productivity obtained in batch culture (3L) of 1.5 days of culture were 4.5gDW, 1.3gDW, 1.8g and 17.4mgL<SUP>-1</SUP>h<SUP>-1</SUP>, respectively. In continuous culture without total cell recycling (TCR), the planktonic biomass was leached, but immobilized biomass reached a steady state at an estimated 6.6gDW. 11.5g of surfactin was produced after 3 days of culture, this gave an average surfactin productivity of 54.7mgL<SUP>-1</SUP>h<SUP>-1</SUP> for the continuous culture, which presented a surfactin productivity of 30mgL<SUP>-1</SUP>h<SUP>-1</SUP> at the steady state. TCR was then investigated for the continuous production, extraction and purification of surfactin using a coupled ultrafiltration step. In continuous culture with TCR at a dilution rate of 0.1h<SUP>-1</SUP>, planktonic biomass, immobilized biomass, surfactin production and productivity reached 7.5gDW, 5.5gDW, 7.1g and 41.6mgL<SUP>-1</SUP>h<SUP>-1</SUP> respectively, after 2 days of culture. After this time, biomass and surfactin productions stopped. Increasing dilution rate to 0.2h<SUP>-1</SUP> led to the resumption of biomass and surfactin production and these values reached 11.1gDW, 10.5gDW, 7.9g and 110.1mgL<SUP>-1</SUP>h<SUP>-1</SUP>, respectively, after 3 days of culture. This study has therefore shown that with this new integrated bioprocess, it was possible to continuously extract and purify several grams of biosurfactant, with purity up to 95%.