Twelve of 79 strains of the genus Lactobacillus, mainly isolated from plants or fermenting material, were found to inhibit at least one of the nine indicator strains of the species Lact. brevis, Pediococcus damnosus and Leucanostoc oenos. The antimicrobial activities from Lact. brevis B 37 and Lact. casei B 80 were caused by polypeptides detectable in the culture liquids. They are bacteriocins with a narrow antimicrobial spectrum. Brevicin 37 from Lact. brevis B 37 was active against many lactic acid bacteria and Nocardia corallina, whereas caseicin 80 from Lact. casei B 80 inhibits only one other strain of Lact. casei. Brevicin 37 is stable at 121d̀C, caseicin 80 is inactivated above 60d̀C, and both are inactivated under alkaline conditions.

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The killer toxin KT 28 of Saccharomyces cerevisiae strain 28 is primarily bound to the mannoprotein of the cell wall of sensitive yeasts. The mannoprotein of S. cerevisiae X 2180 was purified; gel filtration and SDS-PAGE indicated an estimated Mr of 185,000. The ability to bind killer toxin KT 28 increased during purification of the mannoprotein. Removing the protein part of the mannoprotein by enzymic digestion or removing the alkali-labile oligosaccharide chains by beta-elimination did not destroy the ability to bind killer toxin KT 28. However, binding activity was lost when the 1,6-alpha-linkages of the outer carbohydrate backbone were hydrolysed by acetolysis. The separated oligomannosides of the side chains also failed to bind toxin, indicating that the main mannoside chains were essential for the receptor activity. The reversible adsorption of killer toxin to mannoprotein was demonstrated by linking it covalently to Sepharose and using this material for affinity chromatography. A 90-fold increase in the specific activity of a preparation of killer toxin KT 28 was achieved in this way.

A total of 13 killer toxin producing strains belonging to the genera Saccharomyces, Candida and Pichia were tested against each other and against a sensitive yeast strain. Based on the activity of the toxins 4 different toxins of Saccharomyces cerevisiae, 2 different toxins of Pichia and one toxin of Candida were recognized. The culture filtrate of Pichia and Candida showed a much smaller activity than the strains of Saccharomyces. Extracellular killer toxins of 3 types of Saccharomyces were concentrated and partially purified. The pH optimum and the isoelectric point were determined. The killer toxins of S. cerevisiae strain NCYC 738, strain 399 and strain 28 were glycoproteins and had a molecular weight of Mr = 16,000. The amino acid composition of the toxin type K2 of S. cerevisiae strain 399 was determined and compared with the composition of two other toxins.

Since the first description by Bevan and Makower (3), different types of killer yeasts have been observed in Saccharomyces cerevisiae and in various yeast genera (21). The best-known killer strains of S. cerevisiae have been designated K1 to K3; these strains kill one another but are immune to the killer toxin of their own class. The action of the killer toxin of type K1 starts with an energy-independent step by adsorbing to primary receptors of the cell wall of a susceptible yeast strain. Subsequently, the killer toxin alters the cell membrane, which becomes permeable to protons and metabolites. Finally the susceptible yeast cell dies. The killer toxin-resistant mutants (krel and kre2) adsorbed much less killer toxin than does the wild-type strain (1). Spheroplasts of the mutants krel and kre2 were susceptible to killer toxin. Therefore, it was assumed that the primary binding site is located in the cell wall (1). The receptor for K1 killer toxin was identified as P-1,6-D-glucan. The killer toxin KT28 of S. cerevisiae 28 is different from known killer toxins, although it resembles the K2 type. They have similar amino acid compositions and are glycoproteins with similar molecular weights and similar isoelectric points (14). Killer toxin KT28 is bound to the mannoprotein part of the yeast cell wall, and this property has been used for the purification of KT28 (16a). By P-elimination and acetolysis it was demonstrated that the mannose side chains of the outer chain of the carbohydrate component of the mannoprotein were essential for adsorption. In this paper, it is shown that adsorption of killer toxin KT28 can be prevented by concanavalin A, which binds to the D-mannopyranose rings of the mannoprotein. Experiments with biochemically defined mannoprotein mutants (2) should demonstrate which molecular structure of mannan is essential for adsorption of killer toxin KT28.

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The evaporation of water through a plastic membrane coated with plant was (30-70 μg cm(2)) from grape berries or fractions thereof was determined. The hydrocarbon, alcohol and aldehyde fractions caused the highest reduction of evaporation. Their effect was identical to the complete wax or to mineral paraffin wax. The main constituent of the grape cuticle wax, the triterpene oleanolic acid, had no effect on evaporation in the artificial system. Free docosanoic acid did not suppress evaporation whereas the mixture of free fatty acids (the main constituents are the C24 and C26 acids) from grape wax reduced evaporation slightly. The results from this artificial system suggest that the alcohol, hydrocarbon and aldehyde fractions are the active components of the grape cuticle which prevent water loss.

SummaryThe fine structure of the surface wax of leaves of sultana vines (Vitia viiUJera var. sultana) has been examined using the carbon replica technique. Leaf wax was found to be morphologically similar to the wax on the surface of grapes and to consist of a series of overlapping platelets. A brief period (30 sec) of exposure to light petroleum vapour disorganized the platelet structure of both leaf and fruit wax. This treatment markedly increased the cuticular transpiration of both fruits and leaves. The results are discussed in relation to the known chemical composition of these waxes. It is suggested that the surface wax, which consists of overlapping platelets that are hydrophobic in nature, may be important in controlling cuticular transpiration in both the fruit and leaves of grape.vines.