Example experiment of the assay sketched in panel C. Cells previously grown at 0.3 h − 1 in continuous culture are starved (green circles). After 2 days of starvation, a sample is (1) extracted and (2) UV-sterilized, see dashed line, followed by (3) inoculation of 1% of starved and (4) growth of the culture. The difference between the maximum viability after growth, and the initial viability at point (3) is the absolute yield. 