Yeasts belong to the kingdom Fungi of the five kingdom classification of living organisms. The other four are – animalia, plantae, protista and monera. If there were ever a prize for organisms that contributed most to the success today in biotechnology – I think budding yeast would be a top runner up. What is budding yeast ? The easiest way to learn is by thinking about the word – budding. This yeast produces its progeny by budding – this is a way of its asexual reproduction. The scientific name is Saccharomyces cerevisiae.
There are many varieties of budding yeast that are commonly used in the biotechnology in contrast to that used in academic research labs. Of course, the selection of biotech yeasts is mostly towards those which are good for brewing. Brewing is the production of alcoholic beverages by natural process of fermentation. The chief characteristics of the brewing yeasts can be summed up in six major points – they should have a minimal lag phase of growth, they should show high fermentation rate compared to cell growth, they should show efficient production of ethanol, they should be able to withstand differences in alcohol concentrations and osmotic pressure, they should give reproducible amount of flavor and aroma, they should have ideal flocculation character and they should be easy to handle to be able for use in future.
In contrast to this the strains that are used for academic research have to be genetically very well characterized – their genotypes should be known. The knowledge is further used for genetic modification when required. The deletion of certain genes can cause a metabolite to accumulate and cause colour formation – which could further be used to distinguish two different strains. In addition, the laboratory yeast strains are often worked with haploid mating types. What is haploid and what is diploid ? Haploid yeast have half the chromosome numbers as diploids. Haploids come in two flavours – a type and alpha type. The a and alpha type can mate with one another but not in themselves. The diploid are not bad either in surviving – when there is a shortage of nutrients the diploids can undergo sporulation to form spores. Upon arrival of favourable conditions the spores germinate to form haploid yeasts. One of the big advantages of yeasts in research is that the complete genome is available, so it possible to mutate a gene and look for its function or tag a gene with reporter and look at the localization of the protein. Further, these process have become easy to do because of our understanding of the homologous recombination in yeasts.