Browsing by Author "Mwenje, Eddie"

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    Extracellular cellulase production by tropical isolates of Aureobasidium pullulans
    (NRC Canada, 2005-01) Kudanga, T.; Mwenje, Eddie
    Cellulase production by Aureobasidium pullulans from the temperate regions has remained speculative, with most studies reporting no activity at all. In the current study, tropical isolates from diverse sources were screened for cellulase production. Isolates were grown on a synthetic medium containing cell walls of Msasa tree (Brachystegia sp.) as the sole carbon source, and their cellulolytic activities were measured using carboxymethyl cellulose and α-cellulose as substrates. All isolates studied produced carboxymethyl cellulase (endoglucanase) and alpha-cellulase (exoglucanase) activity. Endoglucanase-specific activities of ten selected isolates ranged from 2.375 to 12.884 μmol glucose·(mg protein)–1·h–1, while activities on α-cellulose (exoglucanase activity) ranged from 0.293 to 22.442 μmol glucose·(mg protein)–1·day–1. Carboxymethyl cellulose induced the highest cellulase activity in the selected isolates, while the isolates showed variable responses to nitrogen sources. The current study indicates that some isolates of A. pullulans of tropical origin produce significant extracellular cellulolytic activity and that crude cell walls may be good inducers of cellulolytic activity in A. pullulans.
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    Molecular characterisation of Armillaria species from Zimbabwe
    (The British Mycological Society, 2003-01) Mwenje, Eddie; Wingfield, Brenda D.; Coetzee, Martin P.A.
    Armillaria species are amongst the most important pathogens of trees and have a world-wide distribution. In recent years, the taxonomy of Northern Hemisphere Armillaria spp. has been extensively treated, but those occurring in Africa are poorly known. Previously, isolates of Armillaria from Zimbabwe have been grouped based on morphology and biochemical tests. In this study, six isolates representing the three previously characterized groups of Armillaria spp. occurring in Zimbabwe were analysed using DNA-based techniques. Three distinct clusters emerged from both PCR–RFLP and analysis of sequence data for the IGS-1 rRNA operon. The three groups corresponded to those previously identified based on morphology and biochemical tests. Differences in IGS-1 sequences strongly suggest that the Zimbabwean groups represent three distinct taxa. Isolates belonging to Group I, previously assumed to be to A. heimii, were similar to those identified as A. fuscipes from South Africa and La Reunion. Group II isolates resided in a clade apart from all other isolates and appear to represent A. heimii. The remaining isolates residing in Group III clustered with isolates from Zambia and Cameroon. These are different from A. heimii and A. fuscipes and apparently represent an undescribed taxon.