not show a high growth rate under anaerobic conditions,
which was a common characteristic of S. cerevisiae. Therefore,
low growth of the strain DMKU 3-1042 used in this
study might have been caused by insufficient aeration of
the system. In addition, D’Amore et al. (1989) reported
that increasing the cell density resulted in an increase in
ethanol production at high temperature. Hence, in order
to address this problem, increasing the initial cell concentration
together with increasing the aeration rate might
be necessary. Sugar utilization further confirmed the low
ethanol production and yeast cell growth. Condition (2),
where the highest ethanol production and growth were
obtained, gave the lowest sugar concentration remaining
at the end of fermentation: 7.05%. On the other hand,
under Condition (1), with the lowest ethanol production
and growth, the highest concentration of remaining sugar
(10.35%) was observed. For Condition (3) and (4), the concentrations
of remaining sugars were 9.24% and 7.93%,
respectively.
3.5. Identification of the selected thermotolerant yeast strains
Identification of the strain DMKU 3-1042 following a
conventional taxonomic approach was made by comparing
its morphological, biochemical and physiological characteristics
(data not shown) to a taxonomic key of Kurtzman
and Fell (1998). The strain DMKU 3-1042 was revealed to
be K. marxianus. In molecular taxonomic studies on nucleotide
sequences of D1/D2 domain of LSU rDNA showed
that the sequences of the strain DMKU 3-1042 and the
type strain of K. marxianus were i