Abstract
ABSTRACTMbp1p is a component of MBF (MluI cell cycle box binding factor, Mbp1p-Swi6p) and is well known to regulate the G1–S transition of the cell cycle. However, few studies have provided clues regarding its role in fermentation. This work aimed to recognize the function of the MBP1 gene in ethanol fermentation in a wild-type industrial Saccharomyces cerevisiae strain. MBP1 deletion caused an obvious decrease in the final ethanol concentration under oxygen-limited (without agitation), but not under aerobic, conditions (130 rpm). Furthermore, the mbp1Δ strain showed 84% and 35% decreases in respiration intensity under aerobic and oxygen-limited conditions, respectively. These findings indicate that MBP1 plays an important role in responding to variations in oxygen content and is involved in the regulation of respiration and fermentation. Unexpectedly, mbp1Δ also showed pseudohyphal growth, in which cells elongated and remained connected in a multicellular arrangement on yeast extract-peptone-dextrose (YPD) plates. In addition, mbp1Δ showed an increase in cell volume, associated with a decrease in the fraction of budded cells. These results provide more detailed information about the function of MBP1 and suggest some clues to efficiently improve ethanol production by industrially engineered yeast strains.IMPORTANCE Saccharomyces cerevisiae is an especially favorable organism used for ethanol production. However, inhibitors and high osmolarity conferred by fermentation broth, and high concentrations of ethanol as fermentation runs to completion, affect cell growth and ethanol production. Therefore, yeast strains with high performance, such as rapid growth, high tolerance, and high ethanol productivity, are highly desirable. Great efforts have been made to improve their performance by evolutionary engineering, and industrial strains may be a better start than laboratory ones for industrial-scale ethanol production. The significance of our research is uncovering the function of MBP1 in ethanol fermentation in a wild-type industrial S. cerevisiae strain, which may provide clues to engineer better-performance yeast in producing ethanol. Furthermore, the results that lacking MBP1 caused pseudohyphal growth on YPD plates could shed light on the development of xylose-fermenting S. cerevisiae, as using xylose as the sole carbon source also caused pseudohyphal growth.
Highlights
Mbp1p is a component of MBF (MluI cell cycle box binding factor, Mbp1pSwi6p) and is well known to regulate the G1–S transition of the cell cycle
When molasses was used as the sole carbon source, the total sugar with mbp1D and WT decreased from 19.87% 6 0.14% and 19.55 6 0.26% at the beginning of feeding (0 h) to 3.88% 6 0.15% and 3.37% 6 0.07% at 64 h, respectively, and the utilization rate of molasses by mbp1D was 80.5%, lower than that by the WT (82.8%) (Fig. 1A)
MBP1 deletion caused a decrease of tolerance and an obvious decrease in the final ethanol concentration under oxygen-limited conditions
Summary
Mbp1p is a component of MBF (MluI cell cycle box binding factor, Mbp1pSwi6p) and is well known to regulate the G1–S transition of the cell cycle. Mbp1D showed an increase in cell volume, associated with a decrease in the fraction of budded cells These results provide more detailed information about the function of MBP1 and suggest some clues to efficiently improve ethanol production by industrially engineered yeast strains. The significance of our research is uncovering the function of MBP1 in ethanol fermentation in a wild-type industrial S. cerevisiae strain, which may provide clues to engineer better-performance yeast in producing ethanol. Wild-type S. cerevisiae cannot form pseudohyphae, but when cells are starved for nitrogen [10, 11], carbon [12], and especially fermentable sugars [13], they switch from a yeast form to a filamentous pseudohyphal form [11] and invade into agar [13]. Filamentous/invasive growth allows sessile yeast cells to forage for scarce nutritional resources [11, 12]
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