Polyphasic classification of the genus Photorhabdus and proposal of new taxa:: P-luminescens subsp luminescens subsp nov., P-luminescens subsp akhurstii subsp nov., P-luminescens subsp laumondii subsp nov., P.temperata sp nov., P-temperata subsp temperata subsp nov and P-asymbiotica sp nov.

The taxonomic position of Photorhabdus strains was examined through the results of DNA relatedness (S1 nuclease method) studies associated with the determination of Delta T-m, 16S rRNA phylogenetic inferences and phenotypic characterization, including morphological, auxanographic, biochemical and physiological properties. Three genomic species were delineated on a consensus assessment. One of these species corresponded to Photorhabdus luminescens, since strains were at least 50% related to the type strain of this species with Delta T-m less than 7 degrees C. The two other species were novel genomic species II and III, which were less than 40% related to each other with Delta T-m higher than 9 degrees C. A comparison of the complete 16S rDNA sequences of several representatives of genomic species II and genomic species III revealed that each of them formed a stable lineage independent of the cluster generated by P. luminescens strains. The genomic species differed in their maximum temperatures for growth. A correlation with the ecological origin of the bacterial samples was noticed. The heat-tolerant group I (maximum growth temperature 35-39 degrees C) corresponded to the symbionts of Heterorhabditis bacteriophora groups Brecon and HP88 and Heterorhabditis indica, nematodes living in warm and tropical countries, respectively. Group II (maximum growth temperature 33-35 degrees C) encompassed symbionts from Heterorhabditis megidis, Heterorhabditis zealandica and group NC1 of H. bacteriophora, nematodes isolated in temperate climates. Group III were bacteria isolated from human specimens. Two new species, Photorhabdus temperate sp. nov. (type strain CIP 105563(T)) and Photorhabdus asymbiotica sp. nov. (type strain ATCC 43950(T)), are proposed for genomic species II and ill, respectively. Species I and II can be separated into sub-groups on the basis of high DNA-DNA relatedness (more than 80% DNA binding with Delta T-m < 1.5 degrees C), 16S rDNA branching and phenotypic characters. Therefore, we propose that the two species P. luminescens and P. temperata should be subdivided into subspecies as follows: P. luminescens subsp. luminescens subsp. nov. (type strain ATCC 29999(T)), P. luminescens akhurstii subsp. nov. (type strain CIP 105564(T)), P. luminescens subsp. laumondii subsp, nov. (type strain CIP 105565(T)) and P. temperata subsp, temperata subsp. nov.