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Researchers have achieved a high yield of lactic acid per gram of glucose consumed by Kluyveromyces lactis that is devoid of pyruvate dehydrogenase and pyruvate decarboxylase activity but has high levels of lactate dehydrogenase activity. In addition, this technique produces few additional metabolites, which is one of the goals of industrial fermentation.

The development of a homolactic Kluyveromyces lactis yeast strain, which displays high concentration and high productivity of lactic acid at a pH level below 5 to 5.5, the typical minimum pH range for lactate production by conventional microbial cells, is reported. Results represent the first example of a total replacement of a fermentation product mediated by metabolic engineering methods in yeast genera.

Researchers have been able to increase the secretion of human insulin-like growth hormone from yeast by fusing the hIGF-1 gene to the prepro-alpha-factor leader sequence and inactivating the GAS1 gene of the yeast. This hormone is of interest to the pharmaceutical industry.

The possibility of a practical application of the hypoxic regulation of the K1PDC1 promoter is investigated by cloning the whole promoter sequence upstream to several heterologous genes coding for proteins widely heterogeneous in their characteristics is presented. Based on the results it is proposed that the Zygosaccharomyces bailii yeast could be used as K1PDC1 promoter-based expression vectors to achieve heterologous production in a simple and cheap procedure.

The modification of enzyme cofactor concentrations can be used as a method for both studying and engineering metabolism. We varied Saccharomyces cerevisiae mitochondrial NAD levels by altering expression of its specific mitochondrial carriers. Changes in mitochondrial NAD levels affected the overall cellular concentration of this coenzyme and the cellular metabolism. In batch culture, a strain with a severe NAD depletion in mitochondria succeeded in growing, albeit at a low rate, on fully respiratory media. Although the strain increased the efficiency of its oxidative phosphorylation, the ATP concentration was low. Under the same growth conditions, a strain with a mitochondrial NAD concentration higher than that of the wild type similarly displayed a low cellular ATP level, but its growth rate was not affected. In chemostat cultures, when cellular metabolism was fully respiratory, both mutants showed low biomass yields, indicative of impaired energetic efficiency. The two mutants increased their glycolytic fluxes, and as a consequence, the Crabtree effect was triggered at lower dilution rates. Strikingly, the mutants switched from a fully respiratory metabolism to a respirofermentative one at the same specific glucose flux as that of the wild type. This result seems to indicate that the specific glucose uptake rate and/or glycolytic flux should be considered one of the most important independent variables for establishing the long-term Crabtree effect. In cells growing under oxidative conditions, bioenergetic efficiency was affected by both low and high mitochondrial NAD availability, which suggests the existence of a critical mitochondrial NAD concentration in order to achieve optimal mitochondrial functionality.