SCANNING ELECTRON-MICROSCOPY OF THE GUT MICROFLORA OF 2 EARTHWORMS - LUMBRICUS-TERRESTRIS AND OCTOLASION-CYANEUM

Scanning electron microscopy was used to investigate the presence of m icroorganisms, probably bacteria, on the gut surface of earthworms. Th e washed surfaces of the intestines of two earthworms, Lumbricus terre stris and Octolasion cyaneum, were examined. Numerous organisms resemb ling bacteria were observed throughout the gut, some in situations sug gesting attachment. Compared with similar investigations in other inve rtebrates, there were fewer bacteria, showing less morphological diver sity, on the earthworm gut surface. The majority of organisms viewed w ere coccoid, some were filamentous, and a few rod-shaped cells were ob served. Cocci, often in chains, were seen in the foregut of both speci es. Although cocci were also numerous in the midgut region, particular ly in the typhlosole, in 0. cyaneum tufts of segmented, filamentous or ganisms were also seen with some segments resembling spores. Fewer org anisms were found in the hindgut, but in L. terrestris there were segm ented, filamentous organisms, attached to the epithelium by way of a ' 'socket-like'' structure, similar to that by which segmented, filament ous bacteria (SFBs) are attached to the ileum of rats and mice. Transm ission electron microscopy of the hindgut of L. terrestris was underta ken to explore the structure and attachment of SFBs to the gut epithel ium. However, although a few rod-shaped bacteria were observed, no SFB s were located. The observations reported here provide evidence that e arthworms have an attached gut microflora of filamentous microorganism s which are probably indigenous, and as far as we are aware this is th e first published report of such findings in these invertebrates.