Identification of symbiotic bacteria (Photorhabdus and Xenorhabdus) from the entomopathogenic nematodes Heterorhabditis marelatus and Steinernema oregonense based on 16S rDNA sequence

Two species of entomopathogenic nematodes, Heterorhabditis marelatus and St einernema oregonense, were described recently from the west coast of North America. Tt is not known whether the bacterial symbionts of these nematodes are also unique, Here we compared partial 16S rRNA sequences from the symb iotic bacteria of these two nematodes with sequence from previously describ ed Photorhabdus and Xenorhabdus species. The 16S sequence from the new Xeno rhabdus isolate appears very similar to, although not identical to, that of X. bovienii, the common symbiont of S. feltiae. The new Photorhabdus isola te appears to be very distinct from other known Photorhabdus species, altho ugh its closest affinities are with the P, temperata group. We also verifie d a monoxenic association between each isolate and its nematode by amplifyi ng and sequencing bacterial 16S sequence from crushed adult and juvenile ne matodes and from bacterial cultures isolated from infected hosts. (C) 2001 Academic Press.