Taxonomic significance of yeast sphaeroplast release after enzymatic treatment of intact cells

Treatment of whole yeast cells with a mixture of a reducing agent and 1,3-beta-glucanase isolated from Basidiomycete QM806 led to the production of sphaeroplasts from ascomycetes, from some fungi imperfecti, but not from basidiomycetes. Association of 1,3-beta-glucanase with a second enzyme, 1,4-alpha-glucanase, from Trichoderma viride, was required for sphaeroplast release from some, but not all, basidiomycetes and fungi imperfecti. The ability of yeast cells to liberate sphaeroplasts following appropriate enzymic treatment is proposed as a taxonomic criterion for differentiating basidiomycetous from ascomycetous yeasts and for classifying fungi imperfecti yeasts.

[Release of "Saccharomyces cerevisiae" protoplasts: scanning electron microscope study (author's transl)]

In a previous study we described the minimal methodology used to obtain protoplasts from ascomycetous yeasts. Using a reducing agent associated with 1,3-beta-glucanase at 26 degrees C, protoplasts were invariably obtained. In the present study we localized the disruption spots of the cell wall using the two same reagents. The observations were made with the scanning electron microscope. The disruption site was always in the subterminal region, and this very simple structure (proteins with disulphide bridges and 1,3-beta-glucans) was opposite the birth-scar. The dissociation of the two reagents showed that a small part of the yeast population was able to release protoplasts with only glucanase. We believe these very sensitive yeasts (2 to 10% population) to be very young cells. These disruption sites seemed very different from budding-sites. They might be identical with elongation-sites, or with the opening in the ascus-wall during germinating ascospore release.

[Titration of the hemolytic activity of human complement after radial diffusion]

The hemolytic activity of human complement is evaluated after diffusion in agarose containing sensitized erythrocytes. The results show a linear relation between hemolysis area and logarithm of concentration.

[Action of various beta(1-3)-D-glucanases on the wall of yeasts: taxonomic applications]

Purified beta-(1-3)-D-glucanases (from Aspergillus nidulans, Badidiomycetes sp. QM 806, Trichoderma viride) are used to release protoplasts from various yeasts. Two of them may prove taxonomic correlation. The enzyme of Basidomycetes sp. releases protoplasts from Ascomycetes, the enzyme of T. viride releases protoplasts from Ascomycetes and Heterobasidiomycetes; none of them acts on the Basidiomycetes.

[The enzymatic hydrolysis of cell wall applied to yeasts classification (author's transl)]

The rigid structure of yeast cell wall may be a taxonomic criterion. Using the Helix pomatia juice (with mercaptoethylamine hydrochloride) as a polyenzymatic system, we have always obtained protoplasts from ascomycetous yeasts and never from basidiomycetous yeasts tested. Then, we have applied this enzymatic analysis to the Fungi imperfecti yeasts and, according to this test, separated genus looking like basidiomycetous behaviour: Trichosporon, Pityrosporum, Rhodotorula, Cryptococcus and non fermentative Candida (group II). Oppositely, we have put together the Fungi imperfecti yeasts looking like ascomycetous behaviour: Kloeckera, Trigonopsis, Brettanomyces and fermentative Candida (group I). With the second lytic system made of mercaptoethylamine-HCl and beta-(1-3)-D-glucanase, we have selected ascomycetous yeasts giving protoplasts: Saccharomycoidea with genus Saccharomyces, Kluyveromyces, Pichia, Hansenula, Citeromyces, Debaryomyces; we have joined Saccharomycodes and Hanseniaspora to this second group. The other ascomycetous yeasts studied did not give protoplasts with the definite lytic system made of purified beta-(1-3)-D-glucanase and thiol. These results seem to demonstrate that the structure of cell wall can act as an important taxonomic criterion.