ISSN:
1476-5535
Keywords:
Keywords: acetophenone; baker’s yeast; bioreduction; chemical tolerance; phenethyl alcohol; Saccharomyces cerevisiae
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Bioreduction of acetophenone (ACP) to phenethyl alcohol (PEA) by baker’s yeast (Saccharomyces cerevisiae), which is highly enantioselective, can be carried out entirely in a resting state using stored carbohydrate, suggesting that a high degree of chemical tolerance might be possible. However, viability and catalytic activity of precultured cells decline steeply within 24 h at initial ACP concentrations 〉0.2% (17 mM). Viability of cells at 0.4% ACP was 1/4 the viability at 0.2% ACP as determined by vital staining, and 〈1% based on colony-forming ability. this sensitivity was observed in suspensions with a cell content of nearly 30% (w/v). longterm pea production is strongly dependent on viability, indicating that the cumulative yield per batch of cells is maximized by maintaining a very low concentration of substrate (0.2%). however, nonviable cells (cfu ml−1 〈1% cells ml−1) can achieve PEA yields up to 1/3 the maximum, an amount representing initial absorption of ACP without further uptake. Regarding population adaptability, when cells surviving the most selective (toxic) concentration of ACP (0.6%) were subcultured in an ACP-free medium and re-reacted, the 24-h percent viabilities (vital staining) and colony-forming frequencies exceeded those of non-selected cells. However, the surviving cells represented only a small fraction (1%) of the recultured progeny. Even at ACP concentrations as low as 0.25% (w/v), surviving cells were unreliable in transmitting and maintaining ACP-tolerance. In addition, there was no evidence that the chemical yield of recultured ACP-tolerant cells (amount of PEA relative to initial amount of ACP) can consistently exceed the maximum yield of an equivalent density of previously unreacted (non-selected) cells. These results indicate that over a broad range of substrate concentrations, rapid replacement of cells may be more cost-effective than maintenance or reuse of viable cells.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1038/sj.jim.2900615
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