Principles of the digestion of microorganisms in the gut of soil millipedes: specificity and possible mechanisms

The digestion of different groups of microorganisms in the gut of the soil millipede Pachyiulus flavipes was studied. Gramnegative aerobic bacteria, bacilli, streptomycetes, coryneform bacteria and fungi of the genus Penicillium, isolated from leaf litter, resisted digestion, whereas the majority of predominating yeasts and fungi, including species of family Dematiaceae, were considerably decreased by gut passage. Microorganisms showed species-dependent sensitivities to the midgut fluid of the diplopod. Those that were found to be sensitive to the digestion were killed after only a few minutes of incubation in the fluid. The separation of the fluid by LH-20 Sephadex chromatography reduced its killing activity markedly. The compounds responsible for the mortality were extracted from the Sephadex with 50% methanol. The microbolytic activity of the midgut fluid related to its protein fraction. When applied separately, neither killing nor protein fractions caused the destruction of the cells. Complete destruction of the cells was observed only when the mixture of the two fractions or the native fluid were applied. The mechanism of the induced autolysis is suggested to play a role in the digestion process. (C) 1998 Elsevier Science B.V.