Oxygen supply to bacterial suspensions of high cell densities by hydrogen peroxide

Abstract

The supply of heterotrophically growing suspensions of Alcaligenes eutrophus PHB⁻4 with oxygen formed by the continuous addition of H₂O₂ in the presence of bovine liver catalase was found to be restricted to well‐defined conditions. The catalase‐H₂O₂ system proved to be suitable during the growth at low cell densities equivalent to 2 g dry weight/liter. When under these conditions the oxygen concentration was held constant at 1.8 mg O₂/liter, the cells grew for 6–8 hr at a rate almost identical to that observed with conventional aeration. However, aeration with H₂O₂ for longer durations (10–20 hr) and at higher cell densities (5−20 g dry weight/liter) led invariably to cell damage and retardation of growth. The impairment of growth observed during the oxygen supply by the catalase−H₂O₂ system was traced back to the formation of gradually increasing steady‐state concentrations of H₂O₂ in the medium. Possible sites of cell damage by H₂O₂ such as membrane function, excretion and function of siderophores, and synthesis of cell polymers have been studied, and the cytotoxic mechanism of low concentrations of H₂O₂ was discussed.