Evidence for the presence of a cellulase gene in the last common ancestor of bilaterian animals

Abstract

Until recently, the textbook view of cellulose hydrolysis in animals was that gut-resident symbiotic organisms such as bacteria or unicellular eukaryotes are responsible for the cellulases produced. This view has been challenged by the characterization and sequencing of endogenous cellulase genes from some invertebrate animals, including plant-parasitic nematodes, arthropods and a mollusc. Most of these genes are completely unrelated in terms of sequence, and their evolutionary origins remain unclear. In the case of plant-parasitic nematodes, it has been suggested that their ancestor obtained a cellulase gene via horizontal gene transfer from a prokaryote, and similar suggestions have been made about a cellulase gene recently discovered in a sea squirt. To improve understanding about the evolution of animal cellulases, we searched for all known types of these enzymes in GenBank, and performed phylogenetic comparisons. Low phylogenetic resolution was found among most of the sequences examined, however, positional identity in the introns of cellulase genes from a termite, a sea squirt and an abalone provided compelling evidence that a similar gene was present in the last common ancestor of protostomes and deuterostomes. In a different enzyme family, cellulases from beetles and plant-parasitic nematodes were found to cluster together. This result questions the idea of lateral gene transfer into the ancestors of the latter, although statistical tests did not allow this possibility to be ruled out. Overall, our results suggest that at least one family of endogenous cellulases may be more widespread in animals than previously thought.

Degradation of Plant-derived Carbohydrates in Wetlands

“…This result suggests the endogenous origin of the Cjxyn10A gene. The phylogenetic analysis also supports the theory that the GHF10 xylanase gene was acquired in the early stage of metazoan animal evolution (Lo et al 2003). The expression analyses of mRNA by the RT-PCR and the in situ hybridization provided evidence to support the endogenous origin of C. japonica enzyme (Fig.…”

Feeding spectra and activity of the freshwater crab Trichodactylus kensleyi (Decapoda: Brachyura: Trichodactylidae) at La Plata basin

“…On the other hand, cellulose is the major source of carbohydrates in the Earth, and traditionally, textbooks indicated non-animal organisms (e.g., bacteria and fungi) as the primary cellulase synthesizers. The widespread belief that animals cannot produce cellulase is now being rejected (Lo et al 2003), and there are studies that prove the endogenous synthesis of these enzymes in decapods (Linton et al 2006). The important amount of vegetal matter in the gut content of T. kensleyi implies some kind of metabolic way for the digestion of cellulose, either by an endogenous capacity or by carrying endosymbiotic organisms as reported for other crustaceans (Zimmer et al 2001).…”

Cellulases from Insects

“…Order and species monophyletic [34], and share similar intron/exon boundaries [35,36]. It is therefore also conceivable that a common ancestor of insects possessed a GH9 cellulase gene and that the GH9 gene was vertically transferred to the extant insects.…”

“…Cellulase genes are unlikely to be stable in genomes because they have been lost from the genomes of model insects such as Anopheles gambiae, Drosophila melanogaster, and Bombyx mori [33,37], and probably from many other species [35]. Cellulase genes are also absent from the recently-sequenced genomes of two butterflies, the monarch Danaus plexippus and the postman Heliconius melpomene [38,39].…”