EFFECTS OF SOIL INVERTEBRATES ON THE SURVIVAL OF SOME GENETICALLY-ENGINEERED BACTERIA IN LEAF-LITTER AND SOIL

Seven bacterial strains, most of them bearing natural or recombinant p lasmids, were introduced in oak leaf litter or soddy-podzolic soil. In these substrata, which contained litter-dwelling diplopods and isopod s, or endogenic earthworms, bacteria survival was followed. In the abs ence of the animals, the numbers of introduced strains gradually decre ased. In the presence of the animals, plasmid-bearing strains of Pseud omonas putida survived at 10(5)-10(7) CFUs g(-1) up to 1.5 months in b oth leaves and soil. The total numbers of bacteria found in excrements from the soil macrofauna were 5-15 times higher than in the food. The numbers of P. putida in the excrements were equal to or higher than i n the food. The numbers of Pseudomonas stutzeri JM302 (pLV1013) and Az ospirillum bra siliense ATCC29710 (pFACII) in the excrements were alwa ys 2-10 times lower than in the food. The digestive fluid taken from t he middle part of the gut of the diplopod Pachyiulus flavipes showed a strong antibacterial activity. Those bacteria with lower survival in the gut appeared to be more sensitive to digestion by the midgut fluid . In contrast, the hindgut fluid did not suppress the viability of P. stutzeri JM302 (pLV1013). We postulate that the introduced bacteria pa rtially survive the midgut passage and then multiply with a high growt h rate in the hindgut of the animals. The environmental consequences o f the interactions between soil invertebrates and the released bacteri a are discussed.