Enzymatic digestive capabilities in geophagous earthworms : origin and activities of cellulolytic enzymes

This study compares the origin and activities of glycolytic enzymes present in the gut contents of some geophagous adult earthworms and demonstrates that all the species did not develop mutualistic relationships with the ingested microorganisms to digest soil organic matter. Although the glycolytic activities were rather weak in the earthworms studied, they possess quite a complete enzymatic system that allows to degrade root and fungal substrates available in soils. Millsonia anomala Omo. from Lamto (Cote d'Ivoire) and Hormogaster elisae Alvarez front El Molar (Madrid) developed a strong mutualistic earthworm-microflora digestion system for hydrolysing cellulose: cellulase produced by ingested microflora is able to degrade cellulose to cellobiose, cellobiase released by the worm itself breaks down cellobiose into D-glucose. Both enzymes found in intestinal contents of Pontoscolex corethrurus Mull. from Palms Sole, Veracruz (Mexico) were produced by ingested soil microflora since they were not found in gut tissue culture. On the contrary, Polypheretima elongata Perr. from Sainte Anne (Martinique), Hyperiodrilus africanus Bedd, and Dichogaster terrae nigrae Omo. et Vld. from Lamto (Cote d'Ivoire) possess a complete enzymatic system for hydrolysing cellulose. They could synthesize cellulolytic enzymes, i.e, cellulase: and cellobiase by themselves. In the course of their digestion, geophagous earthworms seem to display variable adaptative characters which are undoubtedly linked to the different ecological categories and niches.