Killing and hydrolytic activities of the gut fluid of the millipede Pachyiulus flavipes CL Koch on yeast cells

The effect of midgut fluid of the millipede Pachyiulus flavipes on the survival of yeast cultures was examined. Yeast species isolated from leaf litter were found to be extremely sensitive to exposure to the midgut fluid. The cfu counts of the incubated cells decreased 100-fold within 5 min, followed by the complete death of cells within 1 h. In contrast, the species isolated from the invertebrate's gut and excrement showed better survival in the fluid with about 10% of the cells remaining viable after 4h of incubation. The cfu estimates correlated well with O-2 uptake measurements. The rapid death of the sensitive yeast Saccharomyces cerevisiae was accompanied by immediate destruction of its vacuoles, nuclei and membranes; however, the cell walls of the majority of the cells remained intact during 1 h of incubation. Two types of activities, killing and hydrolytic, were recognized in the midgut fluid. LH-20 Sephadex gel chromatography showed that the killing;activity of the midgut fluid was associated with its non-protein fraction. The toxic factors were not inactivated by 10-min boiling, but the activity was eliminated when the midgut fluid was diluted more than 6-fold with 50 mM K-citrate buffer. The protein fraction of the midgut fluid, obtained by using LH-20 Sephadex chromatography, caused cell wall hydrolysis but not the immediate death of the S. cerevisiae cells; the protein pattern of this fraction was found to be similar to that one of the intact midgut fluid. It is suggested that the combined effect of both killing and hydrolytic components is required for the effective digestion of microorganisms in the gut of the millipede P. flavipes. (C) 1998 Elsevier Science Ltd. All rights reserved.