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Here we studied the effects of gut transit through the earthworm Eudrilus eugeniae, on the physicochemical, biochemical, and microbial characteristics of pig slurry, by analyzing fresh casts. The reduction in the dissolved organic C contents in casts we recorded suggests that during digestion, earthworms assimilated labile organic C preferentially, which is a limiting growth factor for them. Furthermore, both microbial biomass and activity in pig slurry were significantly decreased by earthworm gut transit. It appears that E. eugeniae is able to digest microorganisms, although the addition of glucose to the food increased respiration, indicating that growth of microorganisms in casts could be limited by depletion of labile C. Despite reduced microbial biomass and activity, the metabolic diversity of microbial communities was greater in casts than in original pig slurry. Community level physiological profiles obtained from Biolog Ecoplate data revealed that, after earthworm gut transit, the microbial communities in casts and pig slurry were clearly differentiated by their physiological profiles. The results indicate that first stage in vermicomposting of pig slurry by E. eugeniae, i.e., casting, produced changes that will influence the dynamics of the organic matter degradation by reducing forms of N and C available to microorganisms, hence restricting their growth and multiplication. Nevertheless, the reduced microflora of casts was characterized by an increased catabolic potential that might lead to thorough degradation of pig slurry.

Cellulase, amylase, invertase, protease and phosphatase activities in pressmud (PM; filter cake) and PM vermicasts of fresh, 15- and 30-day-old casts of Lampito mauritii and Eudrilus eugeniae decreased considerably with cast age. Enhancement of the activities of these enzymes could be ascribed to the nutrient-rich substrate, active microbial populations and optimal moisture conditions. Aged casts showed reduced enzyme activities because of a decreased moisture content, lower nutrient concentrations and a decline in microbial activity. Earthworm-microbe symbiosis seems to operate in a stepwise fashion, controlling groups of enzymes during the metabolism of PM to keep the flux of nutrients in casts (soil) in balance in the biosphere.

The effects of sublethal concentrations of lead nitrate on the growth and reproduction of the African composting earthworm species, Eudrilus eugeniae, was studied by exposing worms in an organic substrate to lead-nitrate-contaminated food over a period of 76 days. The results revealed that growth was initially affected negatively by the presence of lead, while the maturation rate and cocoon production were not affected. In agreement with other studies on Eisenia fetida, cocoon viability was affected negatively by lead, making this a sensitive toxicity endpoint.

Growth rate change in earthworms is considered to be a suitable endpoint when determining sublethal effects. In this study we evaluated growth and maturation in the vermicomposting earthworm speciesEudrilus eugeniae as marker of sublethal toxicity of copper and zinc. We also compared routes of uptake. Apart from exposing worms experimentally for 73 days to contaminated food, a series of contact filter paper tests was also performed to determine LD50 for copper and zinc. Both copper and zinc at sublethal concentrations affected growth and maturation in worms exposed to contaminated food. These worms had a copper content of 34.5 μg g−1 after 73 days and a zinc content of 184.9 μg g−1, showing a differential uptake. Copper was more toxic than zinc. Also in the contact test worms did take up more zinc than copper and the LD50 (48 h) for copper was 0.011 mg cm−2 and for zinc 0.066 mg cm−2, which translated to body burdens of 6 μg g−1 for copper and 131 μg g−1 for zinc. Indications were that a regulatory mechanism existed for both metals. Both metals were taken up through the body wall at a relatively fast rate. This study indicated that the skin was the major route of metal uptake. This study also showed a poor relation between the two types of tests for purposes of evaluating lethality of zinc and copper.

Earthworm surface casting activity was monitored in Leucaena leucoccephala alley cropping and a no-tree control system. Under L. leucocephala hedgerows, five times more casts (116.8 Mg ha-1 year-1) were deposited than in the inter-row space (24.3 Mg ha-1 year-1) and the no-tree control plots (27.8 Mg ha-1 year-1). Hyperiodrilus africanus and Eudrilus eugeniae were the dominant species in alley and no-tree control plots, respectively. Amounts of nutrients returned to the soil surface by casting were lowest in the no-tree control due to low nutrient concentration in casts of Eudrilus sp. In alley cropping (weighted average of amounts under hedgerow and inter-row space), three times more N, K, Ca, and Mg were recycled to the surface than in the no-tree control plots. The relative contribution of casts to nutrient cycling in alley cropping (nutrients in L. leucocephala prunings plus casts = 100%) was 33% N, 16% P, 6% K, 16% Ca, and 34% Mg. Permanent shading of the vicinity of hedgerows was identified as the most important factor enhancing casting activity.