Comparison of methods for determining Batrachochytrium dendrobatidis zoospore viability

The emerging fungal pathogen Batrachochytrium dendrobatidis (Bd) threatens hundreds of amphibian species globally. During laboratory-based experiments it is often essential to quantify live Bd cells, but a comparison of the effectiveness of methods for counting and assessing the viability of the infectious zoospore life stage has not been done. A direct comparison of staining methods that assess viability will ensure that the most accurate and efficient method is used. Here, we compared the use of 2 relatively cheap common stains, trypan blue and methylene blue, and assessed their accuracy and precision for estimating the viability of Bd zoospores during both manual counting and colorimetric assays. We stained known proportions of killed Bd zoospores (0, 0.25, 0.50, 0.75, and 1.00) with each stain and estimated the proportion of stained (dead) and unstained (viable) cells in each sample using both manual counting and colorimetric assays. Trypan blue was found to be a much more effective stain than methylene blue for both microscopy and colorimetric assays. Additionally, counting zoospores via microscopy was both a more accurate and precise technique. We recommend using manual counts via microscopy using the trypan blue stain for assessing Bd zoospore viability.

The yeast Saccharomyces cerevisiae- the main character in beer brewing

Historically, mankind and yeast developed a relationship that led to the discovery of fermented beverages. Numerous inventions have led to improved technologies and capabilities to optimize fermentation technology on an industrial scale. The role of brewing yeast in the beer-making process is reviewed and its importance as the main character is highlighted. On considering the various outcomes of functions in a brewery, it has been found that these functions are focused on supporting the supply of yeast requirements for fermentation and ultimately to maintain the integrity of the product. The functions/processes include: nutrient supply to the yeast (raw material supply for brewhouse wort production); utilities (supply of water, heat and cooling); quality assurance practices (hygiene practices, microbiological integrity measures and other specifications); plant automation (vessels, pipes, pumps, valves, sensors, stirrers and centrifuges); filtration and packaging (product preservation until consumption); distribution (consumer supply); and marketing (consumer awareness). Considering this value chain of beer production and the 'bottle neck' during production, the spotlight falls on fermentation, the age-old process where yeast transforms wort into beer.

Kinetic model for nitrogen-limited wine fermentations

A physical and mathematical model for wine fermentation kinetics has been developed to predict sugar utilization curves based on experimental data from wine fermentations with various initial nitrogen and sugar concentrations in the juice. The model is based on: (1) yeast cell growth limited by nitrogen; (2) sugar utilization rates and ethanol production rates proportional solely to the number of viable cells; and (3) a death rate for cells proportional to alcohol content. All but one parameter in the model can be estimated from existing data. However, experiments to find this final parameter, a constant describing cell death, indicate that cell death may not be the critical factor in determining fermentation kinetics as cell viability remains significant until sugar utilization has ceased. The model, nevertheless, predicts a transition from normal to sluggish to stuck fermentations as initial nitrogen levels decrease. It also predicts that fermentations with high initial Brix levels may go to completion when supplemented with nitrogen in the form of ammonia. Therefore, we hypothesize that the model is valid but that ethanol causes the yeast cells to become inactive while remaining viable. Experimental verification of the model has been performed using flask-scale experiments. The model has also been used to evaluate the possibility of using nitrogen or viable cell additions to avoid or correct problem (i.e., sluggish or stuck) fermentations.