Fermentation Assays Research Articles

Predominance of malolactic fermentation overd-glucose utilization inLactobacillus plantarum andLactobacillus curvatus wine strains

Two selected wine strains of the genusLactobacillus (L. plantarum 197 andL. curvatus 783) were tested for their ability to complete malolactic fermentation (MLF) in a synthetic medium (PBM-broth) supplemented withL-malic acid (7.5–74.6 mM) andD-glucose (5.5–55 mM). The 24 directed fermentation assays, 12 for each bacterial strain, were carried out at 20°C and pH 3.5. MLF was completed (residualL-malic acid ≤0.2 mM) in eight days in 19 of the 24 fermentation assays, even in the presence of 74.6 mML-malic acid or 55.5 mMD-Glucose utilization was generally simultaneous to MLF but was completed (residual concentrations ≤0.2 mM) only in 6 of the 24 fermentation assays. These results support the use of these strains in directed MLF assays at the very differentL-malic acid andD-glucose concentrations tested.

Relationships between the abilities of streptomycetes to decolorize three anthron-type dyes and to degrade lignocellulose

Fourteen Streptomyces strains known to degrade lignocellulose were screened for their ability to decolorize three anthron-type dyes: Remazol Brilliant Blue R (RBBR), blue poly(vinylamine) sulfonate – anthraquinone dye (Poly B-411), and red poly(vinylamine) sulfonate – anthrapyridone dye (Poly R-478). The relationships between efficiency of dye decolorization and capacity to attack lignocellulose were examined. Good correlation was found between lignocellulose weight losses observed during previous solid-state fermentation assays and the ability to decolorize RBBR and Poly B-411. A poor correlation was observed between Poly R-478 decolorizing activity and lignocellulose-degrading ability. The presence of corn stover lignocellulose in the culture broth enhanced decolorization of the dye by all but one of the strains. The enhancement was thought to involve the increased production of extracellular peroxidases by cultures growing on lignocellulose. The results on oxidation of the three dyes by a commercial horseradish peroxidase indicate that RBBR and Poly B-411 are suitable substrates for analyzing production of peroxidases by Streptomyces spp., while no decolorization of Poly R-478 was observed under the conditions used. However, Poly R-478 decolorizing activity of the Streptomyces may reflect the activity of other enzymes involved in the complex process of lignocellulose degradation. Key words: Streptomyces, lignocellulose, degradation, dye, decolorization.

Effect of chromium on the rate of carbon dioxide evolution from Saccharomyces cerevisiae

Abstract The rate of carbon dioxide evolution by whole yeast cells was measured under conditions of both chromium starvation and availability. Preincubation experiments show that there is no evidence for the view that Saccharomyces cerevisiae can synthesize a biologically important form of chromium from simple chromium(III) salts. Chromium enters the yeast cell, possibly by way of the glucose transport system, and exerts a slight inhibitory effect on the fermentation rate but does not affect the rate of cell growth. Glucose tolerance factor fractions show a stimulatory effect in the yeast fermentation assay irrespective of whether the yeast is chromium depleted. The evidence shows that chromium is not an essential trace element for normal yeast metabolism and hence the activity of glucose tolerance factor preparations is unlikely to be due to a chromium complex as is commonly assumed. Some other as yet unidentified compound or compounds must be responsible for the observed increase in the rate of carbon dioxide evolution.

A FERMENTATION ASSAY FOR WORT ELEMENT AVAILABILITY

In small scale fermentation systems, the maximum growth rate for yeast is attained at a zinc concentration of 0·2 ppm. This is used as a base for a suggested assay for zinc availability. The availability of certain elements to the yeast cell can be regulated by certain organic compounds which will act as chelators. Some of these compounds may have the effect of rendering elements unavailable, whereas others may act as messenger molecules and speed up the transport of elements to the yeast cell. The described fermentation assay may be used for the screening of organic compounds for their chelating ability.

Aminopterin Derangement of Yeast Folic Acid Metabolism and Theoretical-Practical Consequences Thereof in Fermentation and Packaging

Stationary and aerated fermentations conducted using synthetic or complex (wort and beer) fermentation media, brewing strains of Saccharomyces cerevisiae and a beer spoilage yeast S. diastaticus, with increasing aminopterin (4-amino folic acid) concentrations are described. The package beer biological preservative studies include synergism examples (EDTA+aminopterin and EDTA+WS-7). Fermentation assays include total yeast cell population/ml of beer, yeast crop dry weight, average cell size, per cent budding and viable cells, cell protein, flocculation, and fermentation liquor pH (indirect measure of fermentation rate). Additional assays include the effect of aminopterin on yeast cell ultrastructure and aerobic respiration. In fermentations conducted with increasing aminopterin concentrations, progressive changes were observed: decreased yeast cell population, dry weight, viability, fermentation rate, and respiration; increased cell size, budding, flocculation, floc formation, and beer pH. Cellular protein remained essentially the same. In electron microscope studies, aminopterin-treated cells showed better fixative penetration and increased formation of lipid inclusions and folds in the cytoplasmic membrane. Aminopterin retarded S. diastaticus growth in package beer. Synergism was also shown. The relationship of results to a change in cell membrane permeability and diacetyl production in beer is discussed.