Antihemocytic surface components of Xenorhabdus nematophilus var. dutki and their modification by serum of nonimmune larvae of Galleria mellonella

Interaction of avirulent transpositional mutants of Xenorhabdus nematophilus ATCC 19061 (Enterobacteriaceae) with the antibacterial systems of non-immune Galleria mellonella (Insecta) larvae.

“…This hypothesis was confirmed for larvae at 2 and 8 h post-infection using a-chymotrypsin to activate the total prophenoloxidase system available and was similar to Xenorhabdus infections in Agrotis segetum (40). The effect of increased LPS concentration on phenoloxidase activity in vitro confirmed reports of LPS inhibiting prophenoloxidase activation (3,14,16,40). The following facts have to be considered in attempting to explain these observations: i) mutants 19061/A and 19061/G formed a high percentage of fragile spheroplasts in the hemolymph that lysed easily in PBS and all the avirulent mutants became extremely hyaline, indicating that factors in the hemolymph modified the cell envelopes; ii) LPS was continuously released during the infections; iii) periplasmic proteins activated the prophenoloxidase cascade in the presence of concentrations of LPS that inhibited its activation with laminarin; iv) serine proteases which are known to activate the prophenoloxidase cascade (8) are present in periplasmic enzymes of X. nematophilus.…”

“…The short-and long-term survival patterns of the X. nematophilus avirulent mutants in G. mellonella larvae are consistent with the idea that LPS is a hemocytotoxin (16). Strain 19061/GF, which had the lowest rate of release of LPS of the strains tested, was removed most efficiently from the hemolymph and was the last to emerge into the hemolymph.…”

“…We also observed that phenoloxidase activity in larvae injected with the X. nematophilus was consistently lower than in insects injected with PBS. Suppression of phenoloxidase activity, which is essential to survival of the vector nematodes (3), has been attributed to the LPS of Xenorhabdus and Photorhabdus species inhibiting the conversion of prophenoloxidase to phenoloxidase (3,16) in all insect species tested (14).…”

“…Nodule formation is independent of the activation of the nematocidal prophenoloxidase system due to the inhibition of the activation of the system by lipopolysaccharides (LPS) released into the hemolymph (16). Bacterial interaction with the hemocytes is mediated by sugars on the outer membrane and by modification of outer membrane proteins induced by hemolymph enzymes (16). The sequestered bacteria proliferate during the initial period within the hemocytes and nodules and subsequently enter the hemolymph following the lysis of the hemocytes.…”

Activation of Prophenoloxidase and Removal of Bacillus subtilis from the Hemolymph of Acheta domesticus (L.) (Orthoptera: Gryllidae)

“…(Fig.2). The enhanced clearance of the bacteria may represents the binding of components of the prophenoloxidase cascade to the bacteria (Silva et al 2000a) and thus removing bacteria by nodulation or bacterial surface modification by serine proteases (Dunphy & Webster 1991).…”