Changes in densities of bacteria and microfungi during gut transit in Lumbricus rubellus and Aporrectodea caliginosa (Oligochaeta: Lumbricidae)

Abstract

Numbers of bacteria, actinomycetes and micromycetes were estimated in gut content samples of specimens of two earthworm species using the plate count technique and the epifluorescence microscopy method. An increase in numbers of all three microbial groups was observed in the intestine of Lumbricus rubellus during the food passage. The total number of palatable aerobic and facultatively anaerobic bacteria was 7 × 10 6 g −1 dry gut content in the foregut, but it increased to 16 × 10 6 and 29 × 10 6 in the midgut and hindgut, respectively. A similar increasing tendency was also observed in numbers of actinomycetes and micromycetes. In contrast higher numbers of bacteria and actinomycetes were detected in the foregut (62 × 10 6, 6 × 10 6 g −1 dry gut content) than in midgut (37 × 10 6, 4 × 10 6) of Aporrectodea caliginosa, and their numbers did not change significantly from midgut to hindgut. Micromycetes were relatively stable in number in all three gut sections. Number of living bacterial cells, estimated by the epifluorescence microscopy method, in general corresponds well with plate counts, although an increase in number of bacteria was detected from midgut to hindgut of A. caliginosa. Factors which would be responsible for differences in the composition of intestinal communities between two earthworm species are discussed.