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Cell-wall structure and composition of Penicillium janczewskii as affected by inulin

     Universidade Metodista de São Paulo, CP 5002, São, Bernardo do Campo, SP 09735-460, Brazil

Glenn Freshour

     The University of Georgia, Complex Carbohydrate, Research Center, 315 Riverbend Road, Athens, Georgia 30602-4712

Rita de Cássia L. Figueiredo-Ribeiro

     Instituto de Botânica, Seção de Fisiologia e Bioquímica, de Plantas, CP 4005, São Paulo, SP 01061-970, Brazil

Michael G. Hahn

     The University of Georgia, Complex Carbohydrate, Research Center, 315 Riverbend Road, Athens, Georgia 30602-4712

Marcia R. Braga ¹

     Instituto de Botânica, Seção de Fisiologia e Bioquímica, de Plantas, CP 4005, São Paulo, SP 01061-970, Brazil

Penicillium janczewskii, a filamentous fungus isolated from the rhizosphere of Vernonia herbacea (Asteraceae), grows rapidly on media containing either sucrose or inulin as carbon sources. Maintenance of P. janczewskii on inulin medium induces secretion of proteins with high inulinase activity but results in a mycelium that easily collapses and breaks. We evaluated the influence of inulin on fungal growth and colony morphology and on cell-wall structure and composition in comparison with growth and wall characteristics on sucrose-containing medium. P. janczewskii grown on Czapek medium with agar containing 1% (w/v) sucrose or inulin showed differences in the color and morphology of the colonies, although growth rates were similar on both carbon sources. Scanning-electron microscopy revealed that the hyphae from fungus grown on inulin-containing medium are much thinner than those from fungus cultivated on sucrose. Ultrastructural analysis of 5 d old cultures using transmission-electron microscopy indicated significant differences in the cell-wall thickness between hyphae grown on inulin or sucrose media. No differences were detected in the overall carbohydrate and protein contents of cell walls isolated from cultures grown on the two carbon sources. Glycosyl composition analyses showed glucose and galactose as the predominant neutral monosaccharides in the walls but showed no differences attributable to the carbon source. Glycosyl linkage composition analyses indicated a predominance of 3-linked glucopyranosyl in the hyphal walls when P. janczewskii was grown on inulin-containing medium. Our results suggest that growth on inulin as the sole carbon source results in structural changes in the mycelia of P. janczewskii that lead to mycelial walls with altered physical and biological properties.

Key words: carbohydrates, electron transmission microscopy, filamentous fungus, inulin, inulinases, savanna, structural polysaccharides, sucrose, tropical fungus

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