Carbon dioxide triggers recovery from dauer juvenile stage in entomopathogenic nematodes (Heterorhabditis spp.)

Heterorhabditis spp. (Rhabditida: Nematoda) live in a close symbiosis with the bacterium Photorhabdus luminescens. For biocontrol purposes the nematod es are produced in liquid culture pre-incubated with P. luminescens. The ba cteria produce a food signal, inducing dauer juveniles (DJ) to initiate dev elopment. In rhabditid nematodes the exit from this developmentally arreste d third stage DJ is called recovery. Attempts to produce Heterorhabditis sp p. in Liquid culture have often failed due to low and delayed recovery of t he inoculated DJ. The influence of carbon dioxide as a recovery co-factor w as investigated. Increasing concentrations of CO2 enhanced DJ recovery in t he presence of the bacterial food signal. The effect could not be related t o a decline of the pH caused by increasing CO2 concentrations. On the contr ary, at lower pH the DJ recovery decreased. In one experiment a considerabl e spontaneous recovery was observed in the absence of a food signal. This p henomenon and a variable threshold response of the DJ to CO2 lead to the as sumption that they are differently pre-disposed to respond to recovery indu cing signals. Providing the results can be confirmed in laboratory scale bi oreactors, the control of carbon dioxide during nematode liquid culture can help to improve the bioreactor process technology.