Antifoaming agent produced by strains of the entomopathogenic bacterium Xenorhabdus nematophilus and its effect on the development of the insect pathogenic nematode Steinernema carpocapsae DD136

An antifoaming agent was produced by strains of Xenorhabdus nematophilus independent of the type of medium and lipid supplementation. The antifoam was heat stable and susceptible to inactivation at moderately acidic (pH 4-6) and alkaline (pH 7.5-8.0) values, The agent was soluble in chloroform and chloroform-methanol suspensions, resistant to proteolytic digestion, negatively-charged and hydrophobic and may be a lipopeptide. The level of antifoam varied with the bacterial strain and was not correlated with the onset of the stationary phase of strain OP1-7 but it peaked during the early stationary phase for strain 19061. Antifoam release into broth required metabolizing cells and was associated with whole bacterial cells, Nematode growth, reproduction and infective juvenile production was enhanced by the antifoam. Because surfactants conducive to the dispersal of lipids produced similar effects, it is possible that the bacterial antifoam enhanced nematode nutrition directly by increasing the availability of lipids to the animals or indirectly by increasing bacterial activity.