Studies on bacterial reducing activity in relation to age of culture.

Bacterial cells in the logarithmic phase of growth are characterized by an ability to reproduce in fresh media without the initial lag period required by organismns in later phases of development. It would seem that the latter lack certain chemical or physiological properties prerequisite to cell division. The type of changes taking place during what may be called the rejuvenation of the cell has only been incompletely investigated. Penfold (1914) set forth the hypothesis that during the lag phase bacteria formed a substance necessary for cell multiplication, which would diffuse from the cells at the end of the logarithmic phase of growth. Lodge and Hinshelwood (1943) observed that a substance appearing during the lag period could be transferred with inocula or sterile filtrates to fresh media, in which it would reduce the lag of newly introduced organisms. One characteristic which differentiates the rapidly multiplying cell from older cells has long been recognized to be a higher rate of oxygen uptake, generally referred to as endogenous respiration. This has been confirmed recently by Bielig, Kausche, and Haardick (1949) with triphenyltetrazolium chloride and in this laboratory with sodium nitrate (Kopper, 1951a). It was felt that further investigation of this property of cells might yield valuable knowledge regarding the nature of factors associated with anabolic cell activities. The present paper deals with the effect of certain environmental changes on what is here termed the reducing activity of bacteria of different growth phases.