The role of cellulases in monophagous leaf-feeding (phyllovorous) insects has been downplayed, however. Phyllovore nutrient economy was mostly studied in Lepidopteran species as models for other leaf-feeding insects. The nutritive value of cellulase for leaf-feeders had been counted as near zero (Bayer et al., 1998, Friend, 1958 and Schroeder, 1986)

because of its indigestibility in most animals, the theory that Lepidoptera are nitrogen limited, lack of cellulase and associated genes in Lepidopteran SB431542 species (http://butterflybase.ice.mpg.de/), and because leaves are one of the least lignified plant structures (Jung and Allen, 1995), especially compared to wood. Today, the role and presence of cellulases in metazoans is being re-evaluated as such enzymes, in particular the glycoside hydrolase family 9 (GH9) endoglucanases, are found in more and more

clades of life (Davison and Blaxter, 2005). Recent findings of GH9 cellulases in facultatively leaf-feeding grasshoppers (Ademolua and Idowu, 2011) and GH45 cellulases and GH 11 xylanases in phyllovorous beetles (Kirsch et al., 2012, Pauchet and Heckel, 2013 and Pauchet et al., 2010) suggest the role of cellulases for other herbivorous insects needs to be re-evaluated. Even Lepidoptera may not be cellulase-free, as their larval Dasatinib in vitro midgut tissues express large amounts of beta-1,3-glucanase: a bacterial lipopolysaccharide recognition protein which, while not a recognized cellulase, may function as a digestion protein (Pauchet et al., 2009). The three main classes of lignocellulolytic enzymes are endo-beta-1,4-glucanases (EGs; Enzyme Commission: 3.2.1.4), beta-glucosidases (BGLs; EC: 3.2.1.21), and exocellobiohydrolases or exocellulases (CBHs; EC: 3.2.1.91) (Watanabe

and Tokuda, 2010). CBHs hydrolyze cellobiose molecules from the terminal ends of cellulose chains and are most common in bacteria and fungi. CBHs of the GH7 family are conspicuous enzymes in the symbiotic protists of certain termites and in asymbiotic marine isopods (King et al., 2010 and Watanabe and Tokuda, 2010). EGs randomly hydrolyze cellulose chains and the BGLs convert the resulting cello-oligomers like cellobiose and cellotriose into glucose, meaning both are needed to fully digest cellulose polymers Rolziracetam into simple sugars. EG activity alone, however, can mediate limited digestion of cellulose on its surface and amorphous regions. Its activity is usually detected on carboxymethylcellulose (CMC) because of the latter’s high sensitivity to EG activity, high solubility in water, and access denial against CBHs (Lo et al., 2000). Beta-glucosidases are ubiquitous endogenous enzymes in insects. They are not solely involved in cellulose digestion in many cases but can catalyze digestion of many other linkages (Watanabe and Tokuda, 2010).