Nitrogen is an essential
nutrient for
yeast cells on
ethanol fermentation. In order to reveal the promoting mechanisms of organic
nitrogen sources on the
ethanol fermentation by
yeast,
Saccharomyces cerevisiae,
laser tweezers Raman spectroscopy and
single-cell analysis techniques were used to monitored the kinetic of intracellular bio-macromolecules of individual
cells during
fermentation with
urea,
yeast extract,
ammonium nitrate or
ammonium sulfate as the sole
nitrogen source. Major results from this
work were as follows. (1) Organic
nitrogen sources had a promoting effect on the
ethanol fermentation, the
fermentation with
urea and
yeast extract reached the maximum concentration of
ethanol in 14-18 h. ( 2 ) There were no apparent lag phases for the
RNA synthesis of
yeast cells cultured with
urea and
yeast extract. The averaged Raman intensity of
yeast cells at peak of 782 cm-1 in the early stage of
fermentation was stronger than that of cultured with
ammonium nitrate and
ammonium sulfate. The maximum was about 1. 9-2. 1 times of the initial intensity for
urea or
yeast extract, but 1. 2-1. 4 times for
ammonium nitrate and
ammonium sulfate. (3) The
secondary structure of
proteins of partial
cells cultured with
yeast extract was dominated byβ-sheet, while
cells cultured with other
nitrogen sources were dominated by α-helix absolutely. These results bring us the conclusion that the improving effect of organic
nitrogen sources such as
urea and
yeast extract on
ethanol fermentation by
Saccharomyces cerevisiae may be due to that the organic
nitrogen sources can shorten the lag phase of
yeast cells, promote the
RNA synthesis, and promote the transcription and expression of related
genes.