Secreted proteases from Photorhabdus luminescens: separation of the extracellular proteases from the insecticidal Tc toxin complexes

Photorhabdus luminescens secretes both high molecular weight insecticidal t oxin complexes and also a range of extracellular proteases into culture bro th. Previous studies by others have suggested that insecticidal activity of the broth is associated with these proteases. However, by gene cloning and targeted knock-out, we have previously shown that oral insecticidal activi ty is associated with high molecular weight 'toxin complexes' (Tc) encoded by toxin complex or tc genes. Here we further clarify this distinction by b iochemically separating the protease fractions away from the oral insectici dal activity of the Tc proteins. We purified three distinct protease fracti ons from the broth: one consisting of a single species of 55 kDa and two of several putatively related species of similar to 40 kDa. All of these clea rly separate from the oral insecticidal activity associated with the high m olecular weight Tc proteins and also show no effect on insect weight gain f ollowing injection into the haemocoel. Here we examine the substrate prefer ences and inhibitor profiles of these protease fractions and discuss their relationship with those previously described from other P. luminescens stra ins and phase variants. (C) 2000 Elsevier Science Ltd. All rights reserved.