Screening of mushrooms from the woodlands of Zimbabwe: Occurrence of lectins and partial purification of a mucin specific lectin from Boletus edulis.

Mushrooms are known to possess a diversity of bioactive compounds that include lectins, which are proteins or glycoproteins that bind specifically to cell surface carbohydrates, culminating in cell agglutination. The present study describes the screening of lectin activity from ten local mushrooms, namely, Amanita zambiana, Boletus edulis, Cantharellus heinemannianus, Cantharellus miomboensis, Cantharellus symoensii, Lactarius kabansus, Amanita sp., Coprinus sp., Ganoderma lucidum and Trametes strumosa. The lectin content was detected by the haemagglutination activity of mushrooms against sheep and goat erythrocytes. Among the different mushrooms screened Amanita sp., Boletus edulis and Lactarius kabansus showed high lectin activity (39, 617 and 77 HAU/mg mushroom, respectively). Boletus edulis was used for the haemagglutination inhibition assay. A total of twenty sugars and sugar derivatives, namely, α-lactose, D-glucose, D-mannose, D-raffinose, N-acetyl glucosamine, maltose, melibiose, D-ribose, porcine mucin, D-cellobiose, D-arabinose, α-methyl-D-glucoside, methyl-α-D-mannopyranoside, D-trehalose, L-arabinose, L-sorbose, L-lyxose, ß-lactose, DL-xylose, and D-galactose, were used for the haemagglutination inhibition assay. Of the various carbohydrates tested, only porcine mucin was found to be the most potent inhibitor of Boletus lectin. The lectin from Boletus mushroom was partially purified using ammonium sulphate precipitation. The highest lectin activity was observed in the 30%-60% fraction. This study revealed for the first time the occurrence of lectins in the local Zimbabwean mushrooms studied as well as isolation of a novel mucin-specific lectin. The information obtained can be used for further investigation of cell surface sugars, purification and characterisation of glycoproteins and their contribution towards the medicinal properties of local mushrooms.

Characterization of Anti-Salmonella typhi Compounds from Medicinal Mushroom Extracts from Zimbabwe.

Antibiotic resistance has become a global concern and threatens the clinical efficacy of many drugs, leading to increased screening of several sources of potential antimicrobial substances. Mushrooms have long been recognized as a valuable source of nutritive and pharmacologically active compounds. Our previous studies showed that the acetone, ethanol, methanol, and cold water crude extracts of various mushrooms-Amanita and Cantharellus species, Ganoderma lucidum, and Lactarius kabansus-exhibited high antibacterial activity against Salmonella typhi. The objective of this study was to isolate, characterize, and identify antibacterial compounds from these crude mushroom extracts. The crude extracts were separated by preparative thin-layer chromatography. Fractions (n = 99) were obtained and screened for antimicrobial activity against S. typhi by using the MTT assay. Of the isolated components, 13 exhibited high inhibitory activity against the growth of S. typhi, with half-maximal inhibitory concentrations ranging from 206 to 619 µg/mL. Some of the highly potent antibacterial compounds were identified by using liquid chromatography-mass spectrometry. Terpenoids (lucidenic acid M and cavipetin D), a phospholipid (C16 sphinganine), and fatty acid amines (stearamide and palmitic amide) were some of the compounds found to be responsible for the antibacterial activity observed. The importance of local mushrooms as sources of antibacterial compounds was revealed. The high inhibitory activity of some mushroom extracts strongly suggests that the mushrooms contain compounds that have great potential for use in developing therapeutic agents against infections caused by S. typhi.

Phenotypic diversity amongst strains of Pleurotus sajor-caju: implications for cultivation in arid environments.

In arid regions, biodiversity and biomass are limited by water availability, and this problem has been compounded by desertification associated with global climate change. The saprotrophic macrofungi that are indigenous to hot subtropical and tropical regions, such as Pleurotus spp., can play key roles in water sequestration, nutrient cycling, human nutrition, and bioremediation of waste materials. We studied 15 strains of Pleurotus sajor-caju, a widespread and phenotypically-diverse species, to establish variability in growth response and primordium development over a range of stress parameters: osmotic potential (-0.5 to -5 MPa), temperature (5-40 degrees C) and pH (2-12). The initiation of primordia precedes basidiome production and therefore represents a key stage in bioremediation strategies and fungi-driven nutrient cycles. Primordia were produced at low pH (4-6), at suboptimal growth temperatures (< or =25 degrees C), and under moderate water stress (-0.5 to -3.5 MPa). Although the growth windows for different strains were similar, their maximum growth rates and the optimum conditions for growth varied. We discuss the phenotypic diversity of Pleurotus strains and discuss their potential for cultivation, bioremediation and ecological regeneration.