Sterilization of culture systems using oxidation-reduction cycles of iodine for efficient, cost-effective, and sustainable bioprocessing: application for Euglena cultivation and production of paramylon

Abstract

The food and pharmaceutical industries culture microorganisms for a variety of purposes and it is critical to prevent contamination of these cultures. The present study presents an innovative chemical sterilization and neutralization technique in which oxidized iodine complexes (I2, I3(-), HOI) that were formed by the reaction of potassium iodide (KI, 0.3 mM) with calcium hypochlorite (Ca(OCl)2, 0.0006 wt%) are used as sterilants and were then neutralized by addition of sodium dithionite (Na2S2O4, 0.032 mM). When applied to E. gracilis cultivation and production of paramylon (a bioactive beta-1,3 glucose polymer), this iodine-based sterilization system led to 1.2-times higher biomass production than an autoclave-based system, without loss of paramylon content (36.70 +/- 1.33%). This iodine-based sterilization system has five distinct advantages: (i) rapid neutralization of the sterilizing agents (within 1 min), (ii) minimal use of toxic chemicals, (iii) sterilization of the upper-surface of a bioreactor via iodine vapor, (iv) hurdle sterilization by repetitive redox reaction, and (v) no thermal denaturation of vital medium components needed for microbial growth. These features make this method of non-contact vapor-phase sterilization and hurdle sterilization particularly suited for large-scale microbial cultures.