Freeze preservation of synchrony in cultures of enterobacteriaceae synchronized by continuous phasing in phosphate-limited media

In order to achieve synchronization of cell division by continuous phasing, the growth of enteric bacteria has been limited by inorganic phosphate. After a short starvation, the culture was automatically diluted twofold so that the limiting nutrient allowed for one doubling exactly. An automatic device was designed to carry out repeated cycles of growth, starvation and dilution with adjustable periodicity. After 12-24 automatic cycles, which were usually achieved largely overnight, synchronous cell divisions could be observed for several generations in nonlimiting culture conditions. When portions of the phased culture were frozen and kept at low temperature for periods up to several months, these freeze-preserved populations exhibited a synchronous growth upon thawing and cultivation. This technique has thus the potential of providing synchronized cultures of a variety of bacterial strains at the desired time.