The actinomycetes, Gram-positive filamentous bacteria, are the most prolific source of natural occurring antibiotics. At an industrial level, antibiotics from actinomycete strains are produced by means of submerged fermentations, where one of the major factors negatively affecting bioproductivity is the pellet-shaped biomass growth. The immobilization of microorganisms on properly chosen supports prevents cell-cell aggregation resulting in improving the biosynthetic capability. Thus, novel porous biopolymer-based devices are developed by combining melt mixing and particulate leaching. In particular, polycaprolactone (PCL), polyethylene glycol (PEG), and sodium chloride (NaCl) with different grain sizes are used to prepare PCL/PEG/NaCl blends in the melt. These blends are then leached to obtain PCL-based porous membranes that are used as solid support for the growth of Streptomyces coelicolor, a model streptomycete used to produce various antibiotics including the blue colored actinorhodin (ACT). Thereafter, the effect of the devices' characteristics on the bacterial growth and on the production ACT is evaluated. The results showed that ACT production is strongly dependent on the pore size distribution of the device. Moreover, membranes with pores ranging from 90 to 110 μm are able to offer a potential improvement in volumetric productivity of ACT if compared to conventional submerged liquid culture.
Keywords: PCL/PEG membrane; S. coelicolor immobilization; actinorhodin production; melt mixing; particulate leaching.
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