Stimulation of the multiplication of Micrococcus luteus by an autocrine growth factor

Viable cells of Micrococcus luteus secrete a proteineous growth factor (Rpf ) which promotes the resuscitation of dormant, nongrowing cells to yield no rmal, colony-forming bacteria. When washed M. luteus cells were used as an inoculum, there was a pronounced influence of Rpf on the true lag phase and cell growth on lactate minimal medium. In the absence of Rpf, there was no increase in colony-forming units for up to 10 days. When the inoculum cont ained less than 10(5) cells ml(-1), macroscopically observable M. luteus gr owth was not obtained in succinate minimal medium unless Rpf was added. Inc ubation of M. luteus in the stationary phase for 100 h resulted in a failur e of the cells to grow in lactate minimal medium from inocula of small size although the viability of these cells was close to 100% as estimated using agar plates made from lactate minimal medium or rich medium. The underesti mation of viable cells by the most-probable-number (MPN) method in comparsi on with colony-forming units was equivalent to the requirement that at leas t 10(5) cells grown on succinate medium, 10(3) cells from old stationary ph ase, or approximately 10-500 washed cells are required per millilitre of in oculum for growth to lead to visible turbidity. The addition of Rpf in the MPN dilutions led to an increase of the viable cell numbers estimated to ap proximately the same levels as those determined by colony-forming units. Th us, a basic principle of microbiology - "one cell-one culture" - may not be applicable in some circumstances in which the metabolic activity of "start er" cells is not sufficient to produce enough autocrine growth factor to su pport cell multiplication.