Improved production of Daptomycin in an airlift bioreactor by morphologically modified and immobilized cells of Streptomyces roseosporus

Ipsita Chakravarty, Ipsita Chakravarty, Subir Kundu

The increased threat of drug resistance has challenged the existence of several conventional and non-conventional antibiotics in the recent times. Daptomycin is a novel cyclic-lipopeptide antibiotic produced by Streptomyces roseosporus that has progressed as a significant anti-MRSA (methicillin-resistant Staphylococcus aureus) antibiotic. But, the economic practicality of this highly valued secondary metabolite is deterred by its poor production and tedious processing methodology. The present study aims at strategic improvement of Daptomycin production through morphological variations of S. roseosporus cells. Free cells, pelletized cells and immobilized cells on ultra porous refractory brick and silk sachets were investigated for the production of Daptomycin in a lab-scale 2.0 l air-lift bioreactor. The effect(s) of nitrogen source, inoculum size and oxygen stress were analyzed for pellet formation of S. roseosporus. Interestingly, free cells produced 750 mg/l of Daptomycin in a single batch. But, the three phase broth viscosity increased due to vigorous growth of free cells which hampered the oxygen transfer rate. The cell degeneration over the time deterred pellet reusability. 1430 mg/l Daptomycin was produced using pellets for 2 batches. On the contrary, mechanical stability, buoyancy and reusability of refractory bricks and silk sachets were beneficial. Daptomycin production was recorded for 6-8 batches. Immobilized cells on refractory bricks and silk sachets led to 4895 mg/l and 3623 mg/l Daptomycin production respectively. Cell immobilization improved the three phase broth rheology and hence, the hydrodynamics within the reactor. Therefore, whole-cell immobilization could contribute to the ameliorated production of this life-saving drug.