Inspecting the pathogenicity of the integument of Oscheius basothovii following sterilization with sodium hypochlorite

Abstract

Oscheius basothovii is a newly described species of entomopathogenic nematode which was isolated from a grassland in Suikerbosrand Nature Reserve near Johannesburg in South Africa. The nematode has a symbiotic relationship with an insect pathogenic bacteria identified as Serratia sp. strain TEL which is a gram negative, rod shaped Enterobacteria. The pathogenicity of O. basothovii following surface sterilization of infective juveniles in 0.1% sodium hypochlorite solution for the following varying time periods, 0 min (sterile water treatment), 30 min, 60 min, 90 min, 120 min, 150 min and 180 min was investigated. Furthermore, Serratia sp. TEL was isolated from the haemocoel of surface sterilised nematodes and tested for its entomopathogenecity in the absence of its nematode host. Genome annotation of Serratia sp. TEL was conducted to identify and characterize the putative genetic subsystem encoding proteins or virulence factors which may be involved in pathogenicity and virulence. Augustus gene prediction results showed that Serratia sp. TEL has a total of 4618 coding regions, 103 RNAs and 119 of these genes may contribute to pathogenicity. Genes encoding the adhesions were also identified. Adhesions are a type of virulence factor and have been shown to be involved in bacterial pathogenicity in several species of bacteria. The ability of a bacterium to attach to specific surfaces and cells is a critical step in its pathogenicity. Surface sterilised nematodes exposed to sodium hypochlorite (NaClO) for 30 min were able to invade and infect Galleria mellonella larvae, causing 20% mortality within 24 h. Within72 hours 100% larval mortality was observed in all NaClO treated nematodes. It thus appears that bacteria which may have been adhering to the external surface of the integument of the infective juveniles of O. basothovii play no role its pathogenicity towards G. mellonella. Further studies are needed to investigate the compounds secreted by Serratia sp. TEL which would possibly contribute to the entomopathogenecity of the nematode. This information regarding virulence factors will increase our understanding of the potential of O. basothovii as an effective biological control agent.