Philipp Gerhardt

Spectrophotometric determination of refractive index increment for bacterial cells

Abstract A method was developed to use an ordinary spectrophotometer for obtaining the refractive index increment of bacterial cells, enabling determination of their solids content by immersion refractometry. The results agreed well with values for cells of Serratia marcescens obtained previously by two other methods.

Mutualistic dialysis culture of Streptococcus lactis and Candida utilis

Abstract Mutualistic dialysis culture of Streptococcus lactis, which is valuable as a dairy starter, and Candida utilis, which is valuable as single cell protein, was investigated in a batch fermentation system. The bacterium and the yeast were inoculated into separate fermentors connected by an intermediate dialyzer, the membranes of which allowed diffusional exchange of solutes. Lactose fed into the bacterial culture was fermented to lactic acid, which was dialyzed into the yeast culture and consumed so as to relieve product inhibition of the bacterial culture. Consequently, the bacterial cell concentration more than doubled in comparison with a nondialysis control, and yeast cells were produced as byproduct. Although the acid production rate by the bacterium was much faster than the acid consumption rate by the yeast, the primary limiting factor of the process apparently was the solute exchange rate across the membrane.