The Role of the Earthworm, Pheretima (Metaphire) hilgendorfi, in Terrestrial Ecosystem Nutrient Cycling

In the gut tissues and contents of the earthworm Pheretima (Metaphire) hilgendorfi, cellulase activity which contributes to the terrestrial ecosystem nutrient cycling has been detected. The origin of the cellulase production, whether it is the earthworm itself or the microorganisms, has not been established at the molecular level. In our study, a cellulase [endo-β-1,4glucanase (EGase), EC3.2.1.4] gene was identified from the intestine tissue of earthworm P. (M.) hilgendorfi. The cDNA encoding EGase of P. (M.) hilgendorfi (phhEG) is 1,606 bp with an open reading frame of 449 bp, and belonging to glycoside hydrolase family (GHF) 9. The deduced amino acid sequences of the phhEG showed a 74% identity to another earthworm Eisenia andrei, and a 31% identity to the bacterium Thermobifida fusca. The recombinant phhEG produced by wheat germ cell-free protein synthesis system showed an enzymatic activity. The result of zymogram analysis of phhEG showed that the band of enzyme activity appears to have a molecular weight of 50 kDa, which is very similar to the value detected from the intestine tissues and contents extracts of P. (M.) hilgendorfi. These results suggested that the cellulolytic enzyme which functionally degrading cellulose is secreted by the earthworm themselves and not dependent on the symbiotic and ingested microorganisms.