Morphological patterns of Aspergillus niger biofilms and pellets related to lignocellulolytic enzyme productivities

AIMS: To study the morphological patterns of Aspergillus niger during biofilm formation on polyester cloth by using cryo-scanning electron microscopy related to lignocellulolytic enzyme productivity. METHODS AND RESULTS: Biofilm and pellet samples obtained from flask cultures were examined at -80 degrees C in a LEO PV scanning electron microscope. Spore adhesion depends on both its rough surface and adhesive substances that form a pad between spore and support. An extracellular matrix surrounding germ tubes and hyphae was also seen. Biofilm mycelia showed an orderly distribution forming surface and inner channels, while pellets showed highly intertwined superficial hyphae and a densely packed deep mycelium. Morphological differences between both types of culture correlated with differences in enzyme volumetric and specific productivities. Biofilm cultures produced higher filter paper cellulase, endoglucanase, beta-glucosidase and xylanase volumetric and specific productivities than submerged cultures. CONCLUSIONS: Fungal biofilms are morphologically efficient systems for enzyme production. Favourable physiological aspects are shared with solid state fermentation, but fungal biofilms present better possibilities for process control and scale-up. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study support the importance of morphology in the productivity of fungal submerged processes, placing biofilms in a preferential category.