Glycolytic flux increase in Lactococcus cremoris coincides with accelerated pathway decay and reduced cumulative product yield.

Non-growing cells are commonly encountered in nature and often desired in biotechnological applications to maximize product yields. Such cells exhibit limited protein synthesis, and their metabolic functionality relies on the long-term stability and repair of enzymes and pathways to sustain metabolic activity. However, knowledge of the factors that influence prolonged metabolism is lacking. A biotechnological example is the production of lactic acid. Here we show that prolonged lactic acid formation in non-growing, translationally blocked cells, is not constrained by the intrinsic maximum number of catalytic cycles, but by the metabolic flux. Faster conversion coincided with faster pathway decay and importantly lower cumulative product yield, and vice versa. This behavior is consistent irrespective of whether the flux is altered through manganese addition, changing the cellular ATP demand, or enzyme expression levels. The correlation between flux and pathway decay is relevant for biotechnological applications, and the fitness of growth arrested environmental microorganisms.