[Lysine and arginine requirement of "Ustilago cynodontis" 4001 yeast-like cells. I. --Growth in the presence and in the absence of lysine (author's transl)].
For optimal growth, the yeast-like cells of Ustilago cynodontis 4001 (originating from the mycelium 4001 prototroph forms) require the presence of both arginine and lysine. However, in the absence of lysine, growth does occur, but two exponential growth phases can then be observed: a pseudo-lag phase during which the growth rate is slow, and a second, true exponential phase. The initial OD of the culture and the arginine concentration of the medium do not appear to affect the duration of the pseudo-lag phase. The arginine concentration does, however, affect the growth yield. Upon addition of lysine to the culture medium, the period of the pseudo-lag phase is reduced and the growth rate increased. The pseudo-lag phase can be completely suppressed by the addition of adequate amounts of lysine. In the presence of lysine and in the absence of arginine, cells are not capable of multiplication. Addition of arginine initiates growth; whether or not a lag phase occurs depends on the quantity of arginine added. The successive inoculation of cells into lysine-free medium leads to suppression of the pseudo-lag phase but only after three or four passages. Therefore it does not seem that there is selection of cells which do not require lysine during the pseudo-lag phase. It is shown that it is not the modification of the culture medium which suppresses the lysine requirement: the cells which are put to grow in the supernatant of a culture in which a pseudo-lag phase had taken place behave in the same way that when they are inoculated in a new medium. The modification of the cell metabolism itself is discussed.