Occurrence of natural dixenic associations between the symbiont Photorhabdus luminescens and bacteria related to Ochrobactrum spp. in tropical entomopathogenic Heterorhabditis spp. (Nematoda, Rhabditida).

Bacteria naturally associated with the symbiont Photorhabdus luminescens subsp. akhurstii were isolated from the entomopathogenic nematode Heterorhabditis indica. Bacterial isolates distinct from P. luminescens subsp. akhurstii were obtained from 33% of the samples. Fourteen bacterial isolates, from nematodes collected from three different Caribbean islands, were characterized by conventional phenotypic tests, restriction fragment length polymorphism and sequence analyses of PCR-amplified 16S rRNA genes (16S rDNAs). Isolates were grouped into three genotypes, each one being associated with one Caribbean island. Phenotypic characteristics and 16S rDNA analysis showed that the Photorhabdus-associated bacteria were closely related to Ochrobactrum anthropi for the group from Guadeloupe, and to Ochrobactrum intermedium for the two groups from the Dominican Republic and Puerto Rico. No pathogenicity of the Ochrobactrum spp. to the insects Galleria mellonella and Spodoptera littoralis (Lepidoptera) was detected. Since Ochrobactrum spp. are considered as human opportunist pathogens, the mass production of entomopathogenic nematodes for biological control requires strict vigilance.