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Nematodes are frequently cited as underrepresented in faunistic surveys using DNA barcoding with COI. This underrepresentation is generally attributed to a limited presence of nematodes in DNA databases which, in turn, is often ascribed to structural variability and high evolutionary rates in nematode mitochondrial genomes. Empirical evidence, however, indicates that many taxa are readily amplified with primer sets specifically targeted to different nematode families. Here we report the development of a COI reference library of 1726 specimens in the terrestrial plant parasitic nematode superfamily Criconematoidea. Specimens collected during an ecoregion survey of North America were individually photographed, measured, and PCR amplified to produce a 721 bp region of COI for taxonomic analysis. A neighbor-joining tree structured the dataset into 179 haplotype groups that generally conformed to morphospecies in traditional analysis or Barcode Index Numbers (BINs) in the BOLD system, although absent formal BIN membership due to insufficient overlap with the Folmer region of COI. Approximately one-third of the haplotype groups could be associated with previously described species. The geographic distribution of criconematid nematode species suggests a structure influenced by the major habitat types in the United States and Canada. All sequences collected in the ecoregion survey are deposited in BOLD. Key words: Nematoda, DNA barcoding, species distribution. Les nematodes sont souvent cites comme etant sous-representes dans les inventaires faunistiques realises a l'aide de codes a barres de l'ADN avec le gene COI. Cette sous-representation est generalement attribuee a la presence limitee des nematodes dans les bases de donnees ce qui, a son tour, est souvent imputee a la variabilite structurale et a un taux d'evolution eleve chez les genomes mitochondriaux des nematodes. Les evidences empiriques, cependant, indiquent que plusieurs taxons sont aisement amplifies avec des jeux d'amorces ciblant specifiquement les differentes familles de nematodes. Ici, les auteurs rapportent le developpe-ment d'une librairie de reference de sequences COI pour 1726 specimens appartenant a la superfamille des Criconematoidea, des nematodes parasitant des plantes terrestres. Les specimens ont ete recueillis dans le cadre d'un inventaire de l'ecoregion de l'Amerique du Nord. Ils ont ete photographies, mesures et amplifies individuellement pour obtenir une region de 721 pb du gene COI pour des fins d'analyse taxonomique. Un arbre de type neighbor-joining a separe ces specimens en 179 groupes haplotypiques qui etaient generalement conformes aux especes morphologiques definies par une analyse traditionnelle ou encore sur la base des codes numeriques (BIN de << Barcode Index Numbers >>) du repertoire BOLD, bien qu'ils etaient absents de la description des BIN en raison d'un chevauchement insuffisant au sein de la region Folmer du gene COI. Environ le tiers des groupes haplotypiques ont pu etre associes a des especes deja decrites. La distribution geographique des especes de nematodes criconematides suggere une structure influencee par les principaux types d'habitats aux Etats-Unis et au Canada. Toutes les sequences obtenues au terme de cet inventaire de l'ecoregion ont ete deposees dans le repertoire BOLD. [Traduit par la Redaction] Mots-cles: Nematoda, codage a barres de l'ADN, distribution des especes., Introduction A taxonomic reference library can provide essential information for studies of diversity, distribution, and taxon identity. Now, as investigations using environmental and community DNA are generating vast quantities of [...]

We used morphological and genetic identification to document metazoan parasites of cetaceans and pinnipeds from 28 carcasses salvaged in California between 1974 and 2002, including whales, dolphins, porpoises, sea lions, and seals. Nematodes found included Anisakissimplex (s.l.), A. simplex (s.s.), Pseudoterranova decipiens (s.l.), Pseudoterranova sp., Contracaecum ogmorhini (s.l.), Contracaecum sp., Stenurus cf. minor, Pharurus cf. dalli, and Otostrongylus circumlitus. Cestodes found included Phyllobothrium delphini and Tetrabothrius sp. The acanthocephalan Bolbosoma capitatum, and the arthropod Halarachne miroungae, also were documented. Tetrabothrius sp. in the pygmy beaked whale (Mesoplodon peruvianus) and P delphini in the Eastern North Pacific long-beaked common dolphin (Delphinus delphis bairdii) constitute two new host records. Keywords: parasitology, helminths, cetaceans, pinnipeds, California, Metazoan parasites infesting marine mammals, such as whales, dolphins, seals, and sea lions, include digeneans (flukes), cestodes (tapeworms), nematodes (roundworms), acanthocephalans (spiny headed worms), amphipods, hexapods, and acari. These parasites [...]

The reniform nematode (RN), a major agricultural pest particularly on cotton in the United States, is among the major plant-parasitic nematodes for which limited genomic information exists. In this study, over 380 Mb of sequence data were generated from pooled DNA of four adult female RNs and assembled into 67 317 contigs, including 25 904 (38.5%) predicted coding contigs and 41413 (61.5%) noncoding contigs. Most of the characterized repeats were of low complexity (88.9%), and 0.9% of the contigs matched with 53.2% of GenBank ESTs. The most frequent Gene Ontology (GO) terms for molecular function and biological process were protein binding (32%) and embryonic development (20%). Further analysis showed that 741 (1.1%), 94 (0.1%), and 169 (0.25%) RN genomic contigs matched with 1328 (13.9%), 1480 (5.4%), and 1330 (7.4%) supercontigs of Meloidogyne incognita, Brugia malayi, and Pristionchuspacificus, respectively. Chromosome 5 of Caenorhabditis elegans had the highest number of hits to the RN contigs. Seven putative detoxification genes and three carbohydrate-active enzymes (CAZymes) involved in cell wall degradation were studied in more detail. Additionally, kinases, G protein-coupled receptors, and neuropeptides functioning in physiological, developmental, and regulatory processes were identified in the RN genome. Key words: reniform nematode, detoxification genes, nematode parasitism genes, 454 sequencing. Le nematode reniforme (NR), un important ravageur agricole particulierement chez le cotonnier aux Etats-Unis, compte parmi les nematodes parasitaires importants pour lesquels peu d'informations genomiques sont disponibles. Dans ce travail, plus de 380 Mb de donnees de sequence ont ete generees a partir d'un echantillon compose de quatre femelles adultes du NR et ces sequences ont ete assemblees pour former 67 317 contigs. Au total, 25 904 contigs (38,5 %) ont ete predits comme etant codants, tandis que 41 413 (61,5 %) ont ete predits non-codants. Les sequences les plus repetees etaient de faible complexite (88,9 %) et 0,9 % de ces contigs presentaient de l'homologie avec 53,2 % des EST au sein de GenBank. Les classes les plus representees au sein du Gene Ontology (GO) en matiere de fonction moleculaire et de processus biologique correspondaient respectivement a la classe de liaison aux proteines (32 %) et au developpement embryonnaire (20 %). Des analyses approfondies ont montre que 741 (1,1 %), 94 (0,1 %) et 169 (0,25 %) des contigs genomiques du NR etaient homologues a 1328 (13,9 %), 1480 (5,4 %) et 1330 (7,4 %) des super-contigs de Meloidogyne incognita, Brugia malayi et Pristionchuspacificus, respectivement. Le chromosome 5 de Caenorhabditis elegans a fourni le plus grand nombre de contigs homologues chez le NR. Sept genes putatifs de detoxication et trois codant pour des enzymes de degradation des glucides de la paroi (CAZymes) ont ete etudies en detail. De plus, des kinases, des recepteurs couples aux proteines G et des neuropeptides impliques dans les processus physiologiques, le developpement et la regulation ont ete identifies au sein du genome du NR. [Traduit par la Redaction] Mots-cles: nematode reniforme, genes de detoxication, genes de parasitisme du nematode, sequencage 454., Introduction Global crop losses due to plant-parasitic nematodes are estimated to be ~$80 billion annually (Handoo 1998). The reniform nematode (RN), Rotylenchulus reniformis, is an important pest of cotton in [...]

Understanding the mechanisms of host--pathogen interaction can provide crucial information for successfully manipulating their relationships. Because of its genetic background and practical advantages over vertebrate model systems, the nematode Caenorhabditis elegans model has become an attractive host for studying microbial pathogenesis. Here we report a 'Trojan horse' mechanism of bacterial pathogenesis against nematodes. We show that the bacterium Bacillus nematocida B16 lures nematodes by emitting potent volatile organic compounds that are much more attractive to worms than those from ordinary dietary bacteria. Seventeen B. nematocida-attractant volatile organic compounds are identified, and seven are individually confirmed to lure nematodes. Once the bacteria enter the intestine of nematodes, they secrete two proteases with broad substrate ranges but preferentially target essential intestinal proteins, leading to nematode death. This Trojan horse pattern of bacterium-nematode interaction enriches our understanding of microbial pathogenesis. Bacillus nematocida | Caenorhabditis elegans | chemotaxis | pathogen--host interaction | virulence protease doi/ 10.1073/pnas.1007276107

The evolutionary mechanisms maintaining genetic variation in life span, particularly post-reproductive life span, are poorly understood. We characterized the effects of spontaneous mutations on life span in the rhabditid nematodes Caenorhabditis elegans and C. briggsae and standing genetic variance for life span and correlation of life span with fitness in C. briggsae. Mutations decreased mean life span, a signature of directional selection. Mutational correlations between life span and fitness were consistently positive. The average selection coefficient against new mutations in C. briggsae was approximately 2% when homozygous. The pattern of phylogeographic variation in life span is inconsistent with global mutation-selection balance (MSB), but MSB appears to hold at the local level. Standing genetic correlations in C. briggsae reflect mutational correlations at a local scale but not at a broad phylogeographic level. At the local scale, results are broadly consistent with predictions of the 'mutation accumulation' hypothesis for the evolution of aging. Key Words: Mutation--genetic variation--nematode life span--selection. doi: 10.1093/gerona/glp112

Genetic analysis of parasitic nematodes has been a neglected area of research and the basic genetics of this important group of pathogens are poorly understood. Haemonchus contortus is one of the most economically significant livestock parasites worldwide and is a key experimental model for the strongylid nematode group that includes many important human and animal pathogens. We have undertaken a study of the genetics and the mode of mating of this parasite using microsatellite markers. Inheritance studies with autosomal markers demonstrated obligate dioecious sexual reproduction and polyandrous mating that are reported here for the first time in a parasitic helminth and provide the parasite with a mechanism of increasing genetic diversity. The karyotype of the H. contortus, MHco3(ISE) isolate was determined as 2n = 11 or 12. We have developed a panel of microsatellite markers that are tightly linked on the X chromosome and have used them to determine the sex chromosomal karyotype as XO male and XX female. Haplotype analysis using the X-chromosomal markers also demonstrated polyandry, independent of the autosomal marker analysis, and enabled a more direct estimate of the number of male parental genotypes contributing to each brood. This work provides a basis for future forward genetic analysis on H. contortus and related parasitic nematodes.

Members of the Steinernema genus of nematodes are colonized mutualistically by members of the Xenorhabdus genus of bacteria. In nature, Steinernema carpocapsae nematodes are always found in association with Xenorhabdus nematophila bacteria. Thus, this interaction, like many microbe-host associations, appears to be species specific. X. nematophila requires the nilA, nilB, and nilC genes to colonize S. carpocapsae. In this work, we showed that of all the Xenorhabdus species examined, only X. nematophila has the nilA, nilB, and nilC genes. By exposing S. carpocapsae to other Xenorhabdus spp., we established that only X. nematophila is able to colonize S. carpocapsae; therefore, the S. carpocapsae-X, nematophila interaction is species specific. Further, we showed that introduction of the nilA, nilB, and nilC genes into other Xenorhabdus species enables them to colonize the same S. carpocapsae host tissue that is normally colonized by X. nematophila. Finally, sequence analysis supported the idea that the nil genes were horizontally acquired. Our findings indicate that a single genetic locus determines host specificity in this bacteria-animal mutualism and that host range expansion can occur through the acquisition of a small genetic element.

We describe a two-gene cluster encoding a bacteriocin, xenocin, and the cognate immunity protein in the insect-pathogenic bacterium Xenorhabdus nematophila, which infects and kills larval stages of the common crop pest Helicoverpa armigera. The two genes, xcinA and ximB, are present in the genome as a single transcriptional unit, which is regulated under SOS conditions. The stress-inducible promoter was activated by mitomycin C, glucose, and [Fe.sup.3+] depletion and at an elevated temperature when it was tested in Escherichia coli cells. Expression of the xenocin protein alone in E. coli inhibited the growth of this organism. The growth inhibition was abolished when the immunity protein was also present. A recombinant xenocin-immunity protein complex inhibited the growth of E. coli indicator cells when it was added exogenously to a growing culture. Xenocin is an endoribonuclease with an enzymatically active C-terminal domain. Six resident bacterial species (i.e., Bacillus, Enterobacter, Enterococcus, Citrobacter, Serratia, and Stenotrophomonas species) from the H. armigera gut exhibited sensitivity to recombinant xenocin when the organisms were grown under iron-depleted conditions and at a high temperature. Xenocin also inhibited the growth of two Xenorhabdus isolates. This study demonstrates that [Fe.sup.3+] depletion acts as a common cue for synthesis of xenocin by X. nematophila and sensitization of the target strains to the bacteriocin.

Natural selection and neutral processes such as demography, mutation, and gene conversion all contribute to patterns of polymorphism within genomes. Identifying the relative importance of these varied components in evolution provides the principal challenge for population genetics. To address this issue in the nematode Caenorhabditis remanei, I sampled nucleotide polymorphism at 40 loci across the X chromosome. The site-frequency spectrum for these loci provides no evidence for population size change, and one locus presents a candidate for linkage to a target of balancing selection. Selection for codon usage bias leads to the non-neutrality of synonymous sites, and despite its weak magnitude of effect ([N.sub.c]s ~0.1), is responsible for profound patterns of diversity and divergence in the C. remanei genome. Although gene conversion is evident for many loci, biased gene conversion is not identified as a significant evolutionary process in this sample. No consistent association is observed between synonymous-site diversity and linkage-disequilibrium-based estimators of the population recombination parameter, despite theoretical predictions about background selection or widespread genetic hitchhiking, but genetic map-based estimates of recombination are needed to rigorously test for a diversity-recombination relationship. Coalescent simulations also illustrate how a spurious correlation between diversity and linkage-disequilibrium-based estimators of recombination can occur, due in part to the presence of unbiased gene conversion. These results illustrate the influence that subtle natural selection can exert on polymorphism and divergence, in the form of codon usage bias, and demonstrate the potential of C. remanei for detecting natural selection from genomic scans of polymorphism.

The nematodes Caenorhabditis elegans and C briggsae independently evolved self-fertile hermaphroditism from gonochoristic ancestors. C. briggsae has variably divergent orthologs of nearly all genes in the C. elegans sex determination pathway. Their functional characterization has generally relied on reverse genetic approaches, such as RNA interference and cross-species transgene rescue and more recently on deletion mutations. We have taken an unbiased forward mutagenesis approach to isolating zygotic mutations that masculinize all tissues of C briggsae hermaphrodites. The screens identified loss-of-function mutations in the C. briggsae orthologs of tra-1, tra-2, and tra-3. The somatic and germline phenotypes of these mutations are largely identical to those of their C. elegans homologs, including the poorly understood germline feminization of tra-1(lf) males. This overall conservation of Cb-tra phenotypes is in contrast to the fern genes, with which they directly interact and which are significantly divergent in germline function. In addition, we show that in both C. briggsae and C elegans large C-terminal truncations of TRA-1 that retain the DNA-binding domain affect sex determination more strongly than somatic gonad development. Beyond these immediate results, this collection of mutations provides an essential foundation for further comparative genetic analysis of the Caenorhabditis sex determination pathway.

Molecular changes that underlie evolutionary changes in behavior and physiology are not well understood. Dauer formation in Caenorhabditis elegans is a temperature-sensitive process controlled through a network of signaling pathways associated with sensory neurons and is potentially an excellent system in which to investigate molecular changes in neuronal function during evolution. To begin to investigate the evolution of dauer formation in the genus Caenorhabditis at the molecular level, we isolated dauerformation mutations in C. briggsae, a species closely related to the model organism C. elegans. We identified mutations in orthologs of C. elegans genes daf-2 (insulin receptor), daf-3 (Smad), and daf-4 (TGF-[beta] type 2 receptor), as well as genes required for formation of sensory cilia. Phenotypic analyses revealed that functions of these genes are conserved between C. elegans and C. briggsae. Analysis of C. briggsae mutations also revealed a significant difference between the two species in their responses to high temperatures (>26[degrees]). C. elegans is strongly induced to form dauers at temperatures above 26[degrees], near the upper limit for growth of C. elegans. In contrast, C. briggsae, which is capable of growth at higher temperatures than C. elegans, lacks this response.

Two putative orthologs to the human reduced folate carrier (hRFC),folt-1 and folt-2, which share a 40 and 31% identity, respectively, with the hRFC sequence, have been identified in the Caenorhabditis elegans genome. Functional characterization of the open reading frame of the putative folt-1 and folt-2 showed folt-1 to be a specific folate transporter. Transport of folate by folt-1 expressed in a heterologous expression system showed an acidic pH dependence, saturability (apparent [K.sub.m] of 1.23 [+ or -] 0.18 [micro]M), a similar degree of inhibition by reduced and substituted folate derivatives, sensitivity to the anti-inflammatory drug sulfasalazine (apparent [K.sub.i] of 0.13 mM), and inhibition by anion transport inhibitors, e.g., DIDS. Knocking down (silencing) or knocking out the folt-1 gene led to a significant inhibition of folate uptake by intact living C. elegans. We also cloned the 5'-regulatory region of the folt-1 gene and confirmed promoter activity of the construct in vivo in living C. elegans. With the use of the transcriptional fusion construct (i.e., folt-1::GFP), the expression pattern of folt-1 in different tissues of living animal was found to be highest in the pharynx and intestine. Furthermore, folt-1::GFP expression was developmentally and adaptively regulated in vivo. These studies demonstrate for the first time the existence of a specialized folate uptake system in C. elegans that has similar characteristics to the folate uptake process of the human intestine. Thus C. elegans provides a genetically tractable model that can be used to study integrative aspects of the folate uptake process in the context of the whole animal level. integrative transport physiology; folate transport; transport regulation

Mutational bias is a potentially important agent of evolution, but it is difficult to disentangle the effects of mutation from those of natural selection. Mutation- accumulation experiments, in which mutations are allowed to accumulate at very small population size, thus minimizing the efficiency of natural selection, are the best way to separate the effects of mutation from those of selection. Body size varies greatly among species of nematode in the family rhabditidae; mutational biases are both a potential cause and a consequence of that variation. We report data on the cumulative effects of mutations that affect body size in three species of rhabditid nematode that vary fivefold in adult size. Results are very consistent with previous studies of mutations underlying fitness in the same strains: two strains of Caenorhabditis briggsae decline in body size about twice as fast as two strains of C. elegans, with a concomitant higher point estimate of the geuomic mutation rate; the confamilial Oscheius myriophila is intermediate. There is an overall mutational bias, such that mutations reduce size on average, but the bias appears consistent between species. The genetic correlation between mutations that affect size and those underlying fitness is large and positive, on average.

Characterization of mitochondrial genomes from individual Thaumamermis cosgrovei nematodes, obligate parasites of the isopod Armadillidium vulgare, revealed that numerous mtDNA haplotypes, ranging in size from 19 to 34 kb, are maintained in several spatially separated isopod populations. The magnitude and frequency of conspecific mtDNA size variation is unprecedented among all studied size-polymorphic metazoan mitochondrial genomes. To understand the molecular basis of this hypervariation, complete nucleotide sequences of two 77 coagrovei mtDNA haplotypes were determined. A hypervariable segment, residing between the atp6 and rrnL genes, contributes exclusively to T. cosgrovei mtDNA size variation. Within this region, mtDNA coding genes and putative nonfunctional sequences have accumulated substitutions and are duplicated and rearranged to varying extents. Hypervariation at this level has enabled a first insight into the life history of T. cosgrovei. In five A. vulgare hosts infected with multiple nematodes, four carried nematodes with identical mtDNA haplowpes, suggesting that hosts may become infected by ingesting a recently hatched egg clutch or become parasitized by individuals from the same brood prior to dispersal of siblings within the soil.

Parasitic nematodes of the genus Trichinella cause significant food-borne illness and occupy a unique evolutionary position at the base of the phylum Nematoda, unlike the free-living nematode Caenorhabditis elegans. Although the forthcoming genome sequence of Trichinella spiralis can provide invaluable comparative information about nematode biology, a basic framework for understanding the history of the genus Trichinella is needed to maximize its utility. We therefore developed the first robust and comprehensive analysis of the phylogeny and biogeographic history of Trichinella using the variation in three genes (nuclear small-subunit rDNA, and second internal transcribed spacer, mitochondrial large-subunit rDNA, and cytochrome oxidase I DNA) from all 11 recognized taxa. We conclude that (i) although Trichinellidae may have diverged from their closest extant relatives during the Paleozoic, all contemporary species of Trichinella diversified within the last 20 million years through geographic colonization and pervasive host switching among foraging guilds of obligate carnivores; (ii) mammalian carnivores disseminated encapsulated forms from Eurasia to Africa during the late Miocene and Pliocene, and to the Nearctic across the Bering Land Bridge during the Pliocene and Pleistocene, when crown species ultimately diversified; (iii) the greatest risk to human health is posed by those species retaining an ancestral capacity to parasitize a wide range of hosts; and (iv) early hominids may have first acquired Trichinella on the African savannah several million years before swine domestication as their diets shifted from herbivory to facultative carnivory. biogeography | mitochondrial DNA | phylogeny | ribosomal DNA

The nematode exoskeleton is a multilayered structure secreted by the underlying hypodermal cells and mainly composed of small collagens, which are encoded by a large gene family. In previous work, we reported analysis of the C. elegans dpy-31 locus, encoding a hypodermally expressed zinc-metalloprotease of the BMP-1/TOLLOID family essential for viability and cuticle deposition. We have generated a large set of extragenic suppressors of dpy-31 lethality, most of which we show here to be allelic to tile cuticle collagen genes sqt-3 and dpy-17. We analyzed the interaction among dpy,-31, sqt-3, and dpy-17 using a SQT-3-specific antiserum, which was employed in immunofluorescence experiments. Our results support a role for DPY-31 in SQT-3 extracellular processing and suggest that the SQT-3 C-terminal nontrimeric region serves multiple roles during SQT-3 assembly. Different missense mutations of tiffs region have diverse phenotypic consequences, including cold-sensitive lethality. Furthermore, the biochemical and genetic data indicate that the extracellular assemblies of DPY-17 and SQT-3 are interdependent, most likely because the collagens are incorporated into the same cuticular substructure. We find that absence of DPY-17 causes extensive intracellular retention of SQT-3, indicating that formation of the SQT-3-DPY-17 polymer could begin in the intracellular environment before secretion.

A tractable model for studying pathogen-host-vector biology is presented to demonstrate that Caenorhabditis elegans nematodes are able to transmit phage from infected to uninfected bacterial populations. The results indicate that virus transmission increases with worm density and host bacterial abundance, however, transmission decreases with initial phage abundance, perhaps as viruses eliminate available hosts before migration could occur.

The role of GATA-type transcription factors MED-1 and MED-2 in cell specification of mesendoderm in nematode embryos is studied.

Studies in anhydrobiotic plants have defined many genes which are upregulated during desiccation, but comparable studies in invertebrates are at an early stage. To develop a better understanding of invertebrate anhydrobiosis, we have begun to characterise dehydration-inducible genes and their proteins in anhydrobiotic nematodes and bdelloid rotifers; this review emphasises recent findings with a hydrophilic nematode protein. Initial work with the fungivorous nematode Aphelenchus avenae led to the identification of two genes, both of which were markedly induced on slow drying (90-98% relative humidity, 24 hr) and also by osmotic stress, but not by heat or cold or oxidative stresses. The first of these genes encodes a novel protein we have named anhydrin; it is a small, basic polypeptide, with no counterparts in sequence databases, which is predicted to be natively unstructured and highly hydrophilic. The second is a member of the Group 3 LEA protein family; this and other families of LEA proteins are widely described in plants, where they are most commonly associated with the acquisition of desiccation tolerance in maturing seeds. Like anhydrin, the nematode LEA protein, Aav-LEA-1, is highly hydrophilic and a recombinant form has been shown to be unstructured in solution. In vitro functional studies suggest that Aav-LEA-1 is able to stabilise other proteins against desiccation-induced aggregation, which is in keeping with a role of LEA proteins in anhydrobiosis. In vivo, however, Aav-LEA-1 is apparently processed into smaller forms during desiccation. A processing activity was found in protein extracts of dehydrated, but not hydrated, nematodes; these shorter polypeptides are also active anti-aggregants and we hypothesise that processing LEA protein serves to increase the number of active molecules available to the dehydrating animal. Other LEA-like proteins are being identified in nematodes and it seems likely therefore that they will play a major role in the molecular anhydrobiology of invertebrates, as they are thought to do in plants.

We investigated the possibility of positive selection acting on members of the putative seven-pass chemoreceptor superfamily in Caenorhabditis elegans, which comprises [approximately equal to]1,300 genes encoding seven-pass G protein-coupled receptors (GPCRs). Using a maximum-likelihood approach, we conducted statistical tests for evidence of codon sites where the ratio of nonsynonymous substitutions per nonsynonymous site to synonymous substitutions per synonymous site ([d.sub.N]/[d.sub.S]) was > 1. Evidence for positive selection was found only for the srz family, about which virtually nothing specific is known. We extended the annotation of the srz gene family, establishing gene models for 60 srz genes in C. elegans and 28 srz genes in Caenorhabditis briggsae, [d.sub.N]/[d.sub.S] ratios varied dramatically in different regions of the SRZ proteins, peaking in predicted extracellular regions. These regions included 23 sites where evidence of positive selection was highly significant, corresponding remarkably well with regions implicated in ligand binding in other GPCR family members. We interpret these results as indicating that the srz family is under positive selection, probably driven by ligand binding. positive selection | ligand binding | maximum likelihood | synonymous | nonsynonymous

An insertion between iscA and hscB of the Xenorhabdus nematophila iscRSUA-hscBA-fdx locus, predicted to encode Fe-S assembly machinery, prevented colonization of Steinernema carpocapsae nematodes. The insertion disrupted cotranscription of iscA and hscB, but did not reduce hscBA expression, suggesting that X.nematophila requires coordinated expression of the isc.hsc.fdx locus for colonization.