A comparative study between Fusarium solani and Neocosmospora vasinfecta revealed differential profile of fructooligosaccharide production.

Fructooligosaccharides (FOS) are fructose-based oligosaccharides employed as additives to improve the food's nutritional and technological properties. The rhizosphere of plants that accumulate fructopolysaccharides as inulin has been revealed as a source of filamentous fungi. These fungi can produce FOS either by inulin hydrolysis or by biosynthesis from sucrose, including unusual FOS with enhanced prebiotic properties. Here, we investigated the ability of Fusarium solani and Neocosmospora vasinfecta to produce FOS from different carbon sources. Fusarium solani and N. vasinfecta grew preferentially in inulin instead of sucrose, resulting in the FOS production as the result of endo-inulinase activities. N. vasinfecta was also able to produce the FOS 1-kestose and 6-kestose from sucrose, indicating transfructosylating activity, absent in F. solani. Moreover, the results showed how these carbon sources affected fungal cell wall composition and the expression of genes encoding for ß-1,3-glucan synthase and chitin synthase. Inulin and fructose promoted changes in fungal macroscopic characteristics partially explained by alterations in cell wall composition. However, these alterations were not directly correlated with the expression of genes related to cell wall synthesis. Altogether, the results pointed to the potential of both F. solani and N. vasinfecta to produce FOS at specific profiles.

Fructose affecting morphology and inducing ß-fructofuranosidases in Penicillium janczewskii.

Fructose, glucose, and an equimolar mixture of both sugars affected differently hyphae thickness, biomass production and secretion of ß-fructofuranosidase in Penicillium janczewskii. Reduced growth, thinner hyphae and visible injuries were early observed during fungal cultivation in fructose-containing medium, reaching the maximum between 12 and 15 days of culture. Total sugar content from the cell wall was lower when fructose was supplied and polysaccharides lower than 10 kDa predominated, regardless the culture age. Maximal inulinase and invertase activities were detected in culture filtrates after 12 days, excepting in the glucose-containing medium. Structural changes in cell walls coincided with the increase of extracellular enzyme activity in the fructose-containing medium. The fragility of the hyphae might be related with both low carbohydrate content and predominance of low molecular weight glucans in the walls. Data presented here suggest changes in carbohydrate component of the cell walls are induced by the carbon source.

Purification and properties of exo-inulinases from Penicillium janczewskii growing on distinct carbon sources.

Penicillium janczewskii, isolated from the rhizosphere of Vernonia herbacea, grows rapidly on media containing either sucrose or inulin, although inulin more than sucrose induced the production of inulinases. Three different extracellular beta-fructofuranosidases (two inulinases and one invertase) were purified from fungal cultures grown on sucrose or inulin, through precipitation with ammonium sulfate, and anion-exchange, hydrophobic interaction and gel filtration chromatographies. The optimum temperature of the three enzymes was approximately 60 C, optimum pH 4-5.5 and apparent molecular mass of 80 kDa. K(m) and V(max) values determined for invertase on sucrose were respectively 3.7 10(-4) M and 7.9 10(-2) micromol/min/mL, and on inulin 6.3 10(-2) M and 2.09 10(-2) micromol/min/mL. The values of k(m) for the two inulinases were 8.11 10(-4) and 2.62 10(-3) M, being lower for inulin when compared to those obtained for sucrose. The inulinases did not produce oligofructans from inulin, indicating they are primarily exoinulinases. The differences found in inulinase induction patterns when inulin or sucrose was used seem to be related to modifications on the enzyme properties, mainly concerning substrate affinity.

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

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.

Woronin bodies in Penicillium Janczewskii Zaleski

Penicillium janczewskii Zaleski is an efficient microorganism for the production of extracellular inulinases and grows rapidly on medium containing sucrose or inulin as carbon source. Maintenance of this filamentous fungus on inulin medium induces secretion of large amounts of inulinases, but the resulting mycelium has thinner cell walls that easily collapse and break. Woronin bodies in hyphae of P. janczewskii grown on sucrose and inulin substrates were observed. No significant differences in the number, location, size and shape of Woronin bodies and level of plugging were observed in cultures of the fungus grown on the two carbon sources. The data indicate that the presence of Woronin bodies in P. janczewskii could not be associated with more easily damaged hyphae, although the function of these organelles in pore plugging has been confirmed.