INFLUENCE OF L-SORBOSE AND THE CELL-WALL-LYTIC MICROCOCCUS SP ON THE MAJOR POLYMERS OF ASPERGILLUS-FUMIGATUS

L-sorbose, a sugar known to cause paramorphogenesis in fungi, was test ed for its effect on the growth, morphology and major cell-wall consti tuents of the pathogenic fungus Aspergillus fumigatus. L-sorbose induc es colonial paramorphs in Asp. fumigatus. The colonial growth of the f ungus was restricted and the hyphae showed increased branching and sep tation. Such effects were more pronounced as the concentration of L-so rbose in the medium was increased. Cultures of colonial paramorphs tra nsferred to the original medium showed normal growth. The specific gro wth rate and yield of this strain were reduced by 11.5 and 21%, respec tively, on addition of 1% (w/v) sorbose to the medium. The addition of 0.5% sorbose to Asp. fumigatus cultures challenged with Micrococcus s p. enhanced beta-glucanase activity and cell-wall-lytic activity, but reduced the chitinase activity. After 48 h incubation the chitinase ac tivity started to increase accompanied by a decrease in the glucanase and cell-wall-lytic activities, reaching a maximum after 4 days incuba tion. Asp. fumigatus cell walls isolated from the mycelium grown in th e presence of 0.5% sorbose exhibited an increased glucosamine/glucose ratio compared with that of normal growth. The growth inhibition by L- sorbose was aggravated when Asp. fumigatus culture was challenged with Micrococcus sp. Cell walls isolated from mycelia grown in a mixed cul ture supplemented with sorbose showed higher glucosamide/glucose ratio that that obtained from mixed cultures. The variation in the chemical composition of the cell wall is discussed. (C) 1997 Elsevier Science Limited.