The Effect of Endogenous Earthworm Extracts (Aporrectodea molleri) on the Growth of Beneficial Soil Bacteria

Earthworms, which represent the first animal mass, play an important role in improving soil fertilization and biological properties of the rhizosphere. In the present investigation, the authors were interested in studying the post-mortem effect of this considerable biomass on the growth of soil bacteria. Therefore, the effect of crude extracts of freshly harvested earthworms (FHE) and of earthworms starved for 10 days (FE) on the growth of two bacterial strains, Escherichia coli and Pseudomonas fluorescens was investigated in vitro. The efficiency of these two extracts was compared at different concentrations with a conventional medium (NA). The results showed that the efficiency of FHE and FE extracts on bacterial growth was significantly (P <0.05) greater than that of the NA medium. The optimal concentration of the extracts for E. coli and P. fluorescens was, respectively, 2 and 33.33 times lower than the conventional medium. Moreover, the growth rate at those concentrations was more than 3 times greater. Thus, the FHE and FE extracts would be richer in more diverse nutrients and growth factors. Furthermore, the efficiency of the FE extract was, at all concentrations, higher than the FHE extract, which proves that the nutrients are mainly endogenous to earthworms.