Changes in the fatty acid profiles through the digestive tract of the earthworm Lumbricus terrestris L

The gut of many soil arthropods contains a complex and mutualistic microbial community that usually assists the host with digestion. The same is probably true for earthworms, but the nature and function of the microbiota inhabiting their gut are virtually unknown. In this paper, we studied the microbial community in the gut content of the earthworm Lumbricus terrestris L. and in the bulk soil by assessing their fatty acid (FA) profiles. Our results indicated that the total FA concentration in the earthworm gut was about two orders of magnitude greater than in bulk soil, with higher concentration of bacteria (up to 500-fold), fungal and metazoanderived FAs. Several FAs appearing in the gut were not present in bulk soil. PCA analysis revealed that the microbial community in the gut was different from that in the bulk soil, and that significant changes occurred between midgut, hindgut and proctodeum. Cluster analysis of bacterial and fungal-derived FA profiles grouped the bulk soil samples apart from the gut samples, where the hindgut profiles were more closely related to those from the proctodeum than those from the midgut. We showed important changes in the FA concentration and composition occurring at very small spatial scales inside the gut of the earthworm L. terrestris. These results have implications for understanding earthworm digestion, and they suggest that the microbial community in the earthworm gut is not a casual combination of microorganisms already present in the soil. Further study is needed to determine how these gut microbial communities are involved in earthworm digestion processes. # 2006 Elsevier B.V. All rights reserved.