1.2 Introduction on phytopathogenicity, saprophytism

The primary choice of a microorganism (fungus) potentially providing cell wall degrading enzymes should be directed toward one naturally present in plant environment i. e. a phytopathogen or a saprophyte. Considering the ecology, fungi are qualified as "decomposers" in the opposite to plants, the producers and animals, the consumers. Some fungi, called saprotrophs, get nutrients from dead organisms, especially plants. Some other are pathogen, attacking living organisms. Invasive growth thanks to hyphae gets fungi very adapted to penetrate plants. Hyphae diameter (2-10 pm) permit cell penetration and their hyphal growth in several directions allow them to colonize quickly the plant material with very close contact. Many saprotrophs, phytopathogens and other fungi living in plant environment developed tools for gaining energy from plants during their evolution. Cell wall degrading enzymes (CWDE) are one of these tools which are also efficient for bioethanol production. This is the reason why this chapter focuses on CWDE produced and secreted by some fungi.