Earthworms as the vectors of actinomycetes antagonistic to litter decomposer fungi

The ability of earthworms to digest and assimilate microorganisms varies greatly with the earthworm species, its ecological group, character of food and environmental conditions in which earthworms live. In the current study, actinomycetes were isolated from casts of the two endogeic (Aporrectodea caliginosa, Octolasion tyrtaeum) and an epigeic (Dendrobaena octaedra) earthworm to determine the nature of naturally existing actinomycete community in earthworm casts. Earthworms were kept in soil free compartmented chambers containing leaf litter colonized with actinomycetes antagonistic to litter decomposer fungi and actinomycetes not antagonistic to litter decomposer fungi to infer feeding preferences of earthworms. The actinomycete population dynamics of the casts of the earthworms fed with single antagonistic actinomycete species and soil supplemented with these casts were investigated in order to understand the impacts of both endogeic and epigeic earthworms on the dispersal of actinomycetes antagonistic to the decomposer fungi.According to the current study, the cast actinomycete communities of epigeic (i.e. D. octaedra) and endogeic earthworms (i.e. A. caliginosa, O. tyrtaeum) consisted of frequently isolated actinomycetes of the forest floor. All the cast actinomycetes were Streptomyces species and most of them were found to be antagonistic to the common litter and wood decomposer fungi. All the casts had higher actinomycete counts than those in the surrounding soil.When leaf litter inoculated with antagonistic and non-antagonistic actinomycetes was supplied as the food choices for the earthworms, they preferentially consumed some of the highly antagonistic actinomycetes as well as some weakly antagonistic actinomycetes but the order of preference depended on the earthworm species. Many of the actinomycetes antagonistic to litter decomposer fungi survived gut passage but analysis of earthworm casts did not show any increase in actinomycete numbers during gut passage. The actinomycetes in earthworm casts were able to successfully spread into surrounding soil thereby increasing the existing community size of actinomycetes in natural soil.