The use of solid medium to study effects of cadmium, copper and zinc on yeasts and yeast-like fungi: applicability and limitations

A defined solid medium has been used to examine the responses of Aureobasidium pullulans, Saccharomyces cerevisiae and Sporobolomyces roseus to cadmium, copper and zinc. Experiments where aliquot volumes of metal salt solutions were added to wells in the centre of agar plates revealed marked differences between these organisms. The yeast-like fungus A. pullulans was the least sensitive but S. cerevisiae was more sensitive to cadmium than zinc: the reverse was true for S. roseus. Quantitative data, which complemented the qualitative results, were obtained by measurement of metal concentrations in the plates.     

Lead mineral transformation by fungi.

Pyromorphite (Pb5(PO4)3Cl), the most stable lead mineral under a wide range of geochemical conditions [1], can form in urban and industrially contaminated soils [2] [3] [4] [5]. It has been suggested that the low solubility of this mineral could reduce the bioavailability of lead, and several studies have advocated pyromorphite formation as a remediation technique for lead-contaminated land [3] [5] [6], if necessary using addition of phosphate [6]. Many microorganisms can, however, make insoluble soil phosphate bioavailable [7] [8] [9] [10], and the solubilisation of insoluble metal phosphates by free-living and symbiotic fungi has been reported [11] [12] [13] [14] [15]. If pyromorphite can be solubilised by microbial phosphate-solubilising mechanisms, the question arises of what would happen to the released lead. We have now clearly demonstrated that pyromorphite can be solubilised by organic-acid-producing fungi, for example Aspergillus niger, and that plants grown with pyromorphite as sole phosphorus source take up both phosphorus and lead. We have also discovered the production of lead oxalate dihydrate by A. niger during pyromorphite transformation, which is the first recorded biogenic formation of this mineral. These mechanisms of lead solubilisation, or its immobilisation as a novel lead oxalate, have significant implications for metal mobility and transfer to other environmental compartments and organisms. The importance of considering microbial processes when developing remediation techniques for toxic metals in soils is therefore emphasised.     

Comparison of techniques for the assessment of polymorphonuclear leukocyte polarisation in suspension

Summry— Polarisation of polymorphonuclear leukocytes (PMN) is suspension was assessed using three techniques: 1) visual classification; 2) computerized morphometry; and 3) flow cytometry. While visual classification detected the formation, polarisation and type of cytoplasmic extensions produced by PMN, morphometry and flow cytometry detected only the formation of extensions. The area, perimeter and ellipticity were, in general, statistically different for each subtype of PMN-shape identified by visual classification. Furthermore, the magnitude and direction of changes detected by flow cytometry were affected by the use of erythrocyte lysis (during isolation of the cells) and the fixative used prior to analysis. The findings of this study demonstrate that visual classification is a more sensitive, reliable and appropriate assay of PMN polarisation than current morphometric and flow cytometric methods.     

Differentiation and melanin production in hyaline and pigmented strains of Microdochium bolleyi

The effect of various compounds on growth, melanin biosynthesis and cell differentiation was studied in a hyaline (SH25) and a pigmented (SH25B) strain of Microdochium bolleyi. Dark pigment production by the hyaline strain was induced by the presence of DOPA and indole in the medium, both of which are intermediates in the tyrosine pathway of melanin biosynthesis. These substrates also induced conidia and chlamydospore production, structures which were not normally seen in the hyaline strain. The systemic fungicide, tricyclazole, inhibited melanin synthesis in the pigmented strain but not the development of chlamydospore-like cell structures.     

An unusual correlation between insect damage and crop harvested

An experiment is described by which an attempt was made to determine the effect of manurial treatments on the damage caused by the shot-hole borer of tea. Increases in yields of the plots were accompanied by increases in the damage caused by the beetles as measured by the number of broken branches-an unusual correlation between pest damage and harvest ( r =+0.9267). The experiment failed to indicate clearly the cause of increased damage following manuring, but possibly it results from an increase in the number of galleries formed ( r =+0.6547).