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Abstract

Pristionchus pacificus represents a nematode that shares with Caenorhabditis elegans many
technical features and has been developed as a model system in evolutionary developmental
biology. Many important differences on the genetic and molecular level of development, in
particular vulva development, have been identified (for review see Hong & Sommer,
BioEssays, 2006). Intriguingly, Pristionchus also occupies a distinct ecological niche.
Pristionchus nematodes are associated with scarab beetles and have a necromenic life style:
that is, worms invade the beetle as dauer larvae and wait for the insect's death to feed on the
developing microbes on the carcass. It has been suggested that a close association with other
organisms as seen in necromenic nematodes represent a pre-adaptation towards true
parasitsm.
The P. pacificus California strain was selected as reference strain for high-coverage
sequencing and the Washington strain was selected for low-coverage sequencing because it
interbreeds with the California strain. The assembly of the P. pacificus California genome
attains 9-10 fold coverage and is divided into 2,894 supercontigs. It contains 145 Mb of
unique sequence and calculates a total genome size of around 169 Mb. The Washington
polymorphic strain differs from the reference strain on average in 4.3% of all un-gapped
positions in a whole genome alignment.
With 169-Mb and 29,000 predicted protein-coding genes the P. pacificus genome is
substantially larger than the genomes of Caenorhabditis elegans and the human parasite
Brugia malayi. Comparative analysis with C. elegans revealed an elevated number of genes
encoding cytochrome P450 enzymes, glucosyl-transferases and ABC transporters that were
experimentally validated and confirmed. P. pacificus contains cellulase and diapausin genes
and cellulase activity is found in P. pacificus secretions, the first time cellulases have been
identified in nematodes beyond plant parasites. The increase in detoxification and
degradation enzymes is consistent with the Pristionchus life-style and is a pre-requisite for
parasitism. Thus, comparative genomics of three ecologically distinct nematodes offers a
unique opportunity to investigate the correlation between genome structure and life-style. Current studies involve developmental and genetic analysis of various traits associated with
the specific ecological setting of P. pacificus, such as dauer formation, insect recognition by
olfaction, mouth form dimorphism and bacterial association. The talk will provide an
overview on recent studies in P. pacificus genomics, proteomics and ecology.