BIODIVERSITY OF ALCOHOL PRODUCING YEAST- Saccharomyces cerevisiae
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Date
2011
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY
Abstract
Ethanol is quantitatively and economically the world’s premier biotechnological
commodity. Ethanol can be produced from any fermentable carbohydrates by yeasts. A
long term goal of the brewing industry is to identify yeast strains with increased tolerance
to the stresses experienced during the brewing process. A combination of high temperature,
ethanol and sugar tolerance is clearly desirable characteristics in fermentation processes.
Until 1990s, classical tests based on morphology, biochemical and sexual reproduction
characteristics were used for wine yeast identification. Such methods only allowed
discrimination between species and they were laborious, time consuming and imprecise. In
the last decade, the application of several molecular techniques has generated a large
number of studies concerning ecology and biodiversity of indigenous Saccharomyces
cerevisiae strains.
The present investigation is carried out with the objective of isolating ethanologenic
yeasts from different sources and location followed by screening for diversity on basis of
alcohol production and functional characteristics using cultural and molecular methods.
Twenty samples were obtained from different sources and pure isolates were identified as
yeast cultures based on their morphological characters, cultural characters, carbohydrate
assimilation profile and alcohol producing ability. All isolates had alcohol producing ability
but maximum alcohol production was observed with standard yeast culture Saccharomyces
cerevisiae MTCC-172 (67.77 g l-1) followed by isolate APY-4 (67.53 g l-1) and AMY-2
(67.50 g l-1) while isolate AMY-7 produced the least (30 g l-1).
Twenty yeast isolates and standard yeast culture Saccharomyces cerevisiae MTCC-
172 were screened for ethanol tolerance, thermo tolerance, sugar tolerance and
osmotolerance. It was found that isolates exhibited high diversity for tolerance and were
grouped according to it. Based on these results it was observed that isolates APY-4, AMY-
2, AMY-9 and standard culture Saccharomyces cerevisiae - MTCC-172 were best among
all isolates. These four pure cultures were tested for their alcohol producing ability at 40°C
by inoculating them in fermentation medium containing 20% sugar. Four yeast cultures
fermented sugar and produced alcohol at 40°C and 20% sugar concentration. Isolate AMY-
2 showed superior capacity for alcohol production and sugar conversion efficiency (SCE)
while the standard culture Saccharomyces cerevisiae MTCC-172 exhibited better alcohol
production and sugar conversion efficiency (SCE) at 40°C and 20% sugar concentration.
Genomic DNA of 21 pure cultures of Saccharomyces cerevisiae were analyzed by
RAPD technique using fifteen different primers and a dendrogram was constructed. Only
isolates AMY-7 and APY-2 formed separate single element groups in dendrogram. The
dendrogram analysis was compared with analysis formed from assimilation profiles,
cultural characteristics, morphological characteristics and functional characteristics (sugar
conversion efficiency, thermotolerance, osmotolerance, ethanol tolerance and sugar
tolerance) which revealed great biodiversity among the twenty one pure Saccharomyces
cerevisiae cultures.
Based on the present study it is established that the important functional diversity
found for ethanol tolerance, thermotolerance, sugar tolerance and osmotolerance indicate
that the use of wider range of yeast isolates could be outlined and further developed for
valorization. These results can be applied for optimization of alcohol production, brewery
and baking industries as well in tropical countries such as India. Strain biodiversity
represents a fundamental source of specific and also potential rare characteristics, which
contributes to increase the economics of fermentation. This natural biodiversity represents
an essential source for selection of strains possessing desirable characteristics. The use of
molecular method like RAPD helps in elucidation of genetic diversity among the isolated
yeast strains thereby establishing their evolutionary relationships. This will enable
researchers in designing novel strains carrying all desirable characteristics
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Keywords
fungi, yeasts, alcohols, fermentation, sugar, tolerance, productivity, rapd, concentrates, biological development