The nematophagous fungus Pochonia chlamydosporia degrades chitosan, an antifungal compound that severely affects plant pathogenic fungi, but not nematophagous and entomopathogenic fungi. Extracellular proteins from culture filtrates of P. chlamydosporia grown with either colloidal chitin or chitosan as main carbon and nitrogen sources were investigated. Enzymatic assays using FITC-chitin or FITC-chitosan as substrates detected a much higher endochitinolytic activity in chitosan than in chitin culture filtrates. Chitosanolytic activity was detected only when chitosan was present in the culture medium, suggesting that chitosan-degrading enzymes were only induced by chitosan. Conversely, extracellular chitin degrading enzymes were induced by both colloidal chitin and chitosan. Qualitative and quantitative differences in protein accumulation between both culture media were found using proteomic techniques (2-DE and 2-D DIGE). Some expressed proteins under these conditions could be identified using MALDI/TOF-TOF or LC-MS. Proteins related with carbohydrate or protein degradation were the most abundant in chitosan culture filtrates. Our results suggest that chitosan induces expression of hydrolytic enzymes involved in egg-penetration. (C) 2010 Elsevier Inc. All rights reserved.