Genome-wide expression analysis of an industrial strain of Saccharomyces cerevisiae during the initial stages of an industrial lager fermentation identified a strong response from genes involved in the biosynthesis of ergosterol and oxidative stress protection. The induction of the ERG genes was confirmed by Northern analysis and was found to be complemented by a rapid accumulation of ergosterol over the initial 6-h fermentation period. From a test of the metabolic activity of deletion mutants in the ergosterol biosynthesis pathway, it was found that ergosterol is an important factor in restoring the fermentative capacity of the cell after storage. Additionally, similar ERG10 and TRR1 gene expression patterns over the initial 24-h fermentation period highlighted a possible interaction between ergosterol biosynthesis and the oxidative stress response. Further analysis showed that erg mutants producing altered sterols were highly sensitive to oxidative stress-generating compounds. Here we show that genome-wide expression analysis can be used in the commercial environment and was successful in identifying environmental conditions that are important in industrial yeast fermentation.Yeast are subjected to many types of stress and metabolic challenges throughout industrial fermentation processes. These range from the physical (pressure and shearing) to the chemical, such as osmotic shock, oxidative stress, and secondary metabolite toxicity (3). Yeast fermentation is an ancient process, and years of exposure to these conditions have resulted in industrial yeast strains that have evolved mechanisms to adapt to them. However, with the advent of new processes that increase yields or are more cost-effective, different and increased demands have been placed on the yeast. This can lead to conditions that overwhelm yeast defenses, causing defective fermentations with poor sugar utilization, reduced ethanol production, and the synthesis of poor flavor qualities (21,38,55). Increased stress has also been found to have an impact on the activity and longevity properties of the yeast and therefore affect their performance in subsequent fermentations (30,47,53).To better understand the determinants of defective brews, research is often carried out by changing single parameters in model systems that can be reliably reproduced. This process has been very successful in determining the molecular mechanisms involved in protection against individual stresses. However, industrial fermentations are dynamic in nature, with multiple stresses or biological changes interacting simultaneously to cause the physiological traits of the yeast or fermentation parameters. Thus, studying the effect of individual stresses on yeast does not give the full picture of the important environmental parameters in fermentation.

No abstract

✓ Two cases of spinal arteriovenous malformation (AVM) are reported because of a previously unobserved clinical feature: recurrent transient postprandial paresis of the legs. The authors believe the paresis was caused by chronic shunting of blood away from the cord and into the low-resistance AVM. Symptomatic cord ischemia might then be precipitated by vasodilatation in other areas of the body such as the splanchnic, brachial, or uterine vessels. We believe that in some instances this mechanism should be considered as an explanation for episodic neurological deficits seen in association with spinal AVM's.

No abstract