Iron contributes to the antibacterial functions of the haemolymph of Galleria mellonella

Studies with Galleria mellonella larvae and the iron chelating agent EDDA showed that iron was essential for the removal of dead Xenorhabdas nematophila and Bacillus subtilis from the haemolymph. The delay in removal of the bacteria from the iron-restricted haemolymph was attributed to reduced adhesiveness of the haemocytes and prophenoloxidase activity. Iron augmentation returned these activities to control levels. Whereas dead B. subtilis had no effect on the concentration of ferrozine-detectable iron (henceforth iron) in the haemolymph, dead X. nematophila was associated with substantially lower levels of iron as the number of damaged haemocytes increased. Haemocyte lysate lowered the concentrations of iron in both FeCl3 solutions and deproteinized larval serum independent of serum lipids. Haemocyte lysate added to tryptic soybroth lowered the level of iron and limited the growth of X. nematophila. X. nematophila limited iron availability in the plasma by releasing lipopolysaccharides; such a mechanism may be a means of impairing the antimicrobial defences of the insects.