Fig. 4
From: A microbubble-sparged yeast propagation–fermentation process for bioethanol production
Effect of gassing with 1% O2 regular bubbles (RB) or microbubbles (MB) on yeast sterol content during ethanol-producing fermentations. a Schematic diagram showing the experimental approach. Yeast cultures were propagated aerobically in the prototype MB fermenter sparged with 21% O2 as described in the text. The same yeast cells were used to seed fermentation runs sparged with 1% O2 supplied as either RBs or MBs. Samples were removed for sterol and transcriptome analyses 0, 4, 12 and 44 h after commencing fermentation. Experiments were performed in triplicate. b Effects of sparging fermentations with 1% O2 on expression of sterol biosynthesis genes and sterol content. The bar charts show the amounts (μg mg−1 cell dry mass; vertical axes) of the indicated sterols and sterol esters plotted against fermentation time (h). The data are the means and standard deviations for three biological replicates (grey bars, RB fermentation; black bars, MB fermentation). Differentially expressed (≥ twofold, adjusted p ≤ 0.01, n = 3) ‘ERG’ genes are indicated to the left of the simplified ergosterol biosynthesis pathway: black type, no change; red type, up-regulated in both RB and MB fermentations; cyan type, up-regulated in MB fermentation only; orange type, up-regulated in RB fermentation only