Strategies for Yeast Strain Improvement through Metabolic Engineering

Yeast species such as Saccharomyces cerevisiae, Saccharomyces globosus, Saccharomyces carlsbergensis, Saaccharomyces uvarum and apiculate yeasts have been reported to be present in sugar-rich substances such as exudates from plants (palm wine) and skin of some fruits. S. cerevisiae have been indicated to be the dominant yeast species responsible for the fermentation in baking, brewing and wine making. Its general acceptance as the aforementioned importance lead to its popularity and focus on several research activities. The use of recombinant DNA technology has paved way to new biological pathway designs and systems with resultant targeted expression (phenotypes). This is ultimately the aim of metabolic engineering (ME) now employed to increase the productivity of naturally formed metabolite or those not produced by organisms through directed modification of strain without unfavorable mutation. S. cerevisiae, being an anaerobic organism, can be modified to the advantageous trait required in the industry. Findings from literature have shown that yeast thrive on high concentration of ethanol, sugar and low pH values making it amenable to genetic modification by recombinant DNA technology. These properties together with yield improvement, by-products exclusion and enhancement of the performance processes, process control and properties of the cells all form the major target of ME. Yeast cells therefore can be modified for enhanced production of relevant biochemicals such as caffeine, glycerol, propanediol, organic acids, sugar alcohols, isoprenoids, and resveratrol, which serve as food ingredients in the industry. S. cerevisiae have been indicated to be the dominant yeast species responsible for the fermentation in baking, brewing and wine making. Metabolic engineered new genes from foreign organisms can be introduced in yeast and homologous gene can be overproduced as well. Utilization of certain range of substrates by S. cerevisiae for enhanced production of biotechnological products is illustrated using starch, lactose, raffinose, melibiose and xylose consumption. Improvement of the cellular features of strains of interest as well as the process optimization is one of the key biotechnological processes for enhanced performance required during scaling up in industries. S. cerevisiae is indeed a model microorganism that holds a lot of promise for future applications in industrial production processes. It has the potential in production of useful chemical com