The source of Saccharomyces cerevisiae responsible for the natural fermentation of grape must and the dominance of added yeast in wine fermentations have been studied using a strain of Saccharomyces cerevisiae selected for wine-making and labelled for not producing hydrogen sulphide (H2S-) as fermentation starter. It was shown that the source of the Saccharomyces flora of fermenting musts was the winery itself and that a selected yeast starter added initially is able to impose itself on the spontaneous grape juice flora naturally.
Phase-lengths in the cell division cycle of the basidiomycetous yeast Rhodosporidium toruloides Banno in an asynchronous culture at 27° were estimated by using three parameters: cell morphology, DNA synthesis, and nuclear behavior. In the yeast-extract-sucrose medium, one division cycle is 160min, and phase-lengths of G1, S, G2, and M are calculated to be 116min, 27min, 10min, and 7min, respectively, by applying Powell's distribution function. As a dynamic phenomenon, the cell division cycle was presented in a cell clock.
Ammonium (NH4+) uptake in the cyanobacterium Nostoc muscorum ISU (Anabaena ATCC 27893) and interaction of copper (Cu2+) and sulfhydryl agents was studied. N2-grown cells scavenged extracellular NH4+ via two energy-dependent transport systems: the ‘high-’ (Km=11μM, Vmax=0.22nmol/min/mg protein) and ‘low-affinity’ (Km=66μM, Vmax=1.25nmol/min/mg protein). Both transport systems were competitively inhibited by methylamine (high-affinity Ki=20μM; low affinity Ki=80μM), and showed distinct pH profiles. Addition of Cu2+ (0.1μM) stimulated NH4+ uptake by the high-affinity system (Km=8μM, Vmax=0.42nmol/min/mg protein). Similar effect was not observed with other bivalent cations (Hg2+, Ni2+, Zn2+, Mn2+) applied at equimolar concentrations. The sulfhydryl reducing agents, cysteine and dithiothreitol, inhibited the high-affinity system noncompetitively and caused efflux of accumulated NH4+. Cu2+ eliminated the inhibitory effect of sulfhydryl reducing agents on NH4+ uptake. Inhibition of NH4+ uptake by sulfhydryl blocking agents (N-ethylmaleimide or p-chloromercuribenzoate) which was not reversible by Cu2+ suggested that oxidation of available sulfhydryl residues of membrane proteins (carriers) is an important factor in NH4+ translocation in Nostoc muscorum.
Polyacrylamide gel electrophoresis with specific staining for six enzymes was used for comparison of the strains in two biovars in Pseudomonasmaltophilia. The strains in biovar I required methionine for growth, while the strains in biovar II did not. On the basis of the similarity values on the electrophoretic relative mobilities of enzymes, the strains studied were divided into two major clusters. Out of 27 strains, 18 strains in biovar I were included in cluster 1, and two strains in biovar I and seven strains in biovar II were included in cluster 2.
Differential scanning calorimetry (DSC) of double stranded DNA was carried out using plasmid pJL3-TB5 DNA (5277 base pairs), whose entire nucleotide sequence has been determined. The DSC curve for the linear DNA of the plasmid used in the present study gave seven separate peaks including two main peaks which range from 82° to 98°, suggesting that DNA melts independently at several cooperative blocks along the chain. The DSC curve obtained agreed with the histogram of the frequency versus GC content which was constructed from the GC distribution map along the DNA chain of pJL3-TB5. These results are obvious evidence that the thermal transition of DNA occurs blockwise along the molecular chain. The two main peaks were estimated to be due to the heat transition of the two distinct regions, containing 46-50% and 54-58% GC, respectively. DSC of covalently closed circular (ccc-) DNA of the same plasmid did not show any heat transition peak, indicating that ccc-form is stabilized compared with linear form.