AERATION REQUIREMENTS FOR THE GROWTH OF AEROBIC MICROORGANISMS

Abstract

The effect of oxygen, as measured by the sulfite oxidation method, on growth of aerobic bacteria was studied. With Serratia mar-cescens the % yield of cells, based on the amt. of substrate utilized, the total cell concn., and the live cell count, varies directly with aeration efficiency. The cell concentration varies from 9 mg/ml at an effective aeration rate of 0.5 m[image] O2/liter/ minute to 23 mg/ml at an aeration rate of 9 m[image] O2/liter/minute when 4% glucose plus 2% citric acid are used as substrate. The live cell counts corresponding to these dry wts. are 65 x 109/ml and 17 x 1010/ml, respectively. Increase in aeration efficiency of at least 10-fold over that normally used for laboratory culture of aerobes was necessary to obtain the high cell densities. A synthetic medium was developed for growth of S. marcescens in liquid shake culture. Yields of 38% of the total substrate utilized were realized. The highest cell concentration on a dry wt. basis is 29 mg/ml, corresponding to a live cell count of 20.1 x 1010 per ml. Comparison of the cell concn. on a dry wt. basis and the live cell count of a pigmented and a nonpigmented strain of S. marcescens at various aeration efficiencies showed that both strains give the same dry cell concentrations at all effective aeration rates investigated, whereas the maximum live cell count varied from 60 x 109/ml for the nonpigmented strain to 17 x 1010/ ml for the pigmented strain when both cultures utilized the same amount of substrate. The larger cell size of the nonpigmented strain accounts for the observed result.