Nematoden und Bakterien in obligater Symbiose.
1997
Grunder J.M.
Entomopathogenic nematodes of the genus Heterorhabditis are used for the biological control of pest insects in their larval stage. During their free-living period in the soil the nematode locates the hosts by physical and chemical means and enters the insect-hemolymph where it releases the symbiotic bacterium Photorhabdus luminescens. The multiplication of the bacteria within the insect forms the nutritional basis for the development of a new generation of nematodes, which subsequently leave the insect body to attack other hosts in the surrounding soil. During the in vitro multiplication of P. luminescens PW79 a secondary form SW79 occurs spontaneously. It interferes with the symbiosis and inhibits the development and multiplication of the nematode. The investigation of the biology of both forms of bacteria and their symbiosis with nematodes was the main objective of this study. The natural symbiont P. luminescens PW79 and its secondary form SW79 were characterised using bacteriological and chemical methods. The use of antiserum against P. luminescens and its secondary form allowed for the first time to identify the bacteria within the nematode. The original hypothesis of the secondary form being identical to the "permanent form" in the intestinal tract of the nematode was refuted. Using electron microscopy to analyse length and cross sections through the intestinal tract of the nematode, the number of bacteria per nematode was approximately 2700. The results of the studies allowed the demonstration of the life cycle of nematodes and their symbiotic bacteria. Based on these results, recommendations were made as to how to maintain a pure culture of P. luminescens PW79 and to guarantee optimal conditions for the reproduction of the nematodes. By preventing losses of whole batches, the base of commercial mass production of nematodes on solid medium could be markedly improved.
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