Some physiological characters of yeasts from soils and allied habitats

Yeasts of the soil - obscure but precious

Pioneering studies performed in the nineteenth century demonstrated that yeasts are present in below-ground sources. Soils were regarded more as a reservoir for yeasts that reside in habitats above it. Later studies showed that yeast communities in soils are taxonomically diverse and different from those above-ground. Soil yeasts possess extraordinary adaptations that allow them to survive in a wide range of environmental conditions. A few species are promising sources of yeast oils and have been used in agriculture as potential antagonists of soil-borne plant pathogens or as plant growth promoters. Yeasts have been studied mainly in managed soils such as vineyards, orchards and agricultural fields, and to a lesser extent under forests and grasslands. Our knowledge of soil yeasts is further biased towards temperate and boreal forests, whereas data from Africa, the Americas and Asia are scarce. Although soil yeast communities are often species-poor in a single sample, they are more diverse on the biotope level. Soil yeasts display pronounced endemism along with a surprisingly high proportion of currently unidentified species. However, like other soil inhabitants, yeasts are threatened by habitat alterations owing to anthropogenic activities such as agriculture, deforestation and urbanization. In view of the rapid decline of many natural habitats, the study of soil yeasts in undisturbed or low-managed biotopes is extremely valuable. The purpose of this review is to encourage researchers, both biologists and soil scientists, to include soil yeasts in future studies.

Catabolism of benzene compounds by ascomycetous and basidiomycetous yeasts and yeastlike fungi. A literature review and an experimental approach

A literature review is given on growth of yeasts on benzene compounds and on the catabolic pathways involved. Additionally, a yeast collection was screened for assimilation of phenol and 3-hydroxybenzoic acid. Fifteen ascomycetous and thirteen basidiomycetous yeast species were selected and were tested for growth on 84 benzene compounds. It appeared that 63 of these compounds supported growth of one or more yeast species. The black yeast Exophiala jeanselmei assimilated 54 of these compounds. The catechol branch of the 3-oxoadipate pathway and its hydroxyhydroquinone variant were involved in phenol and resorcinol catabolism of ascomycetes as well as of basidiomycetes. However, these two groups of yeasts showed characteristic differences in hydroxybenzoate catabolism. In the yeastlike fungus E. jeanselmei and in basidiomycetes of the genera Cryptococcus, Leucosporidium and Rhodotorula, the protocatechuate branch of the 3-oxoadipate pathway was induced by growth on 3- and 4-hydroxybenzoic acids. In three Trichosporon species and in all ascomycetous yeasts tested, 4-hydroxybenzoic acid was catabolyzed via protocatechuate and hydroxyhydroquinone. These yeasts were unable to cleave protocatechuate. 3-Hydroxybenzoic and 3-hydroxycinnamic acids were catabolized in ascomycetous yeasts via the gentisate pathway, but in basidiomycetes via protocatechuate. Incomplete oxidation of phenol, some chlorophenols, cresols and xylenols was observed in cultures of Candida parapsilosis growing on hydroquinone. Most compounds transformed by the growing culture were also converted by the phenol monooxygenase present in cell-free extracts of this yeast. They did not support growth. The relationship between the ability of ascomycetous yeasts to assimilate n-alkanes, amines and benzene compounds, and the presence of Coenzyme Q9 is discussed.

Assimilation of protocatechuic acid and p-hydroxybenzoic acid as an aid to laboratory identification of Candida parapsilosis and other medically important yeasts

Test for the ability of yeasts isolated from clinical specimens to utilize protocatechuic acid and p-hydroxybenzoic acid were carried out by using techniques that are commonly employed to test assimilation of carbon sources. A total of 60 isolates of Candida parapsilosis and 5 isolates of Candida humicola readily assimilated these two phenolic acids, whereas other Candida species gave uniformly negative results. Cryptococcus albidus, Cryptococcus terreus, and some isolates of Cryptococcus laurentii also assimilated protocatechuate and p-hydroxybenzoate, whereas Cryptococcus neoformans did not. Results of these tests suggest that assimilation of protocatechuate and p-hydroxybenzoate may be a useful characteristic, when used in conjunction with traditional tests, for identifying C. parapsilosis and C. albidus.

The fungal flora of a Boreal forest raw humus

The fungi present in the raw humus under black spruce in the boreal forest of Quebec were studied by the soil-washing technique. Penicillium, Pullularia, and yeasts together comprised 75–94% of isolates from the washings and 42–77% of those from the washed particles. There was evidence that Penicillium spp. existed to a significant extent in the mycelial state. Aspergillus and Tricho-derma spp. were absent or rare. The possible ecological significance of the high incidence of Pullularia and yeasts is discussed.