Strategies for Yeast Strain Improvement through Metabolic Engineering

Abstract

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.