In terms of metabolic activity, glycerol and glucose feedings
reduced the metabolic activity of P. taetrolens cells upon the feedings
took place (10 h) (Fig. 4B). Whereas lactose feeding did not
lead to reduced metabolic activity status throughout all the
co-fermentation, higher C-source availability resulted in reduced
metabolic activities in both whey/glycerol and whey/glucose
co-fermentations (Fig. 4B). No effects were observed on the membrane
integrity during a whey/lactose co-fermentation, showing a
fluorescence level lower than 102 which meant that P. taetrolens
cells retained the membrane integrity throughout the
co-fermentation (Figs. 4C and S2). In contrast, both glucose and
glycerol feedings had a slight detrimental impact on the membrane
integrity. As the histograms in Fig. 4C show, P. taetrolens cells displayed
lower membrane integrity levels under higher C-source