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In its natural habitat, the nematode Caenorhabditis elegans encounters a plethora of other organisms, including many that are pathogenic [1, 2]. The study of interactions between C. elegans and various pathogens has contributed to characterizing key mechanisms of innate immunity [2-4]. However, how C. elegans recognizes different pathogens to mount pathogen-specific immune responses remains still largely unknown [3, 5-8]. Expanding the range of known C. elegans-infecting pathogens and characterizing novel pathogen-specific immune responses are key steps toward answering this question. We report here that the oomycete Myzocytiopsis humicola is a natural pathogen of C. elegans, and we describe its infection strategy. We identify a new host immune response to pathogen exposure that involves induction of members of a previously uncharacterized gene family encoding chitinase-like (CHIL) proteins. We demonstrate that this response is highly specific against M. humicola and antagonizes the infection. We propose that CHIL proteins may diminish the ability of the oomycete to infect by hindering pathogen attachment to the host cuticle. This work expands our knowledge of natural eukaryotic pathogens of C. elegans and introduces a new pathosystem to address how animal hosts recognize and respond to oomycete infections.

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The beta class of the carbonic anhydrase (CA) enzyme family has been found in plants, yeast, bacteria and algae, but not in animals. Also, little is known concerning the CAs of C. elegans. Genes possibly encoding beta-CAs were revealed by in silico analysis of the C. elegans genome. Amino acid sequence and 3D structure analysis revealed a resemblance to both plant and cab-type beta-CAs. Temporal expression patterns of the two genes, as well as changes in expression levels under different atmospheric conditions (stress) were analyzed by real-time RT-PCR. Recombinant enzymes, expressed in E. coli were used for in vitro measurement of CA activity, while a yeast complementation experiment was performed in order to assess their ability to complement the function of S. crevisieae beta-CA (NCE103) in vivo. RNAi by feeding was performed on wild-type populations that were then examined for a visible phenotype under normal or various stress conditions (pH, CO(2)/O(2)). Two genes possibly encoding beta-CAs were revealed (bca-1 and y116a8c.28). Their products contain elements of both plant and cab-type CAs. Both assays showed that Y116a8c.28 is an active CA. Both genes showed significant levels of transcript accumulation during development, while they also responded to the stress conditions. No visible phenotype was scored under normal or stress conditions.

This study examined the effects of three lactic acid bacteria (LAB) strains on the nematode Caenorhabditis elegans. Lactobacillus salivarius, Lactobacillus reuteri, and Pediococcus acidilactici were found to inhibit the development and growth of the worm. Compared to Escherichia coli used as the control, L. reuteri and P. acidilactici reduced the lifespan of wild-type and short-lived daf-16 worms. On the contrary, L. salivarius extended the lifespan of daf-16 worms when used live, but reduced it as UV-killed bacteria. The three LAB induced the expression of genes involved in pathogen response and inhibited the growth of tumor-like germ cells, without affecting DAF16 localization or increasing corpse cells. Our results suggest the possible use of C. elegans as a model for studying the antitumor attributes of LAB. The negative effects of these LAB strains on the nematode also indicate their potential use against parasitic nematodes.

In this study, in silico analysis of the Caenorhabditis elegans genome revealed six genes (cah-1, cah-2, cah-3, cah-4, cah-5, and cah-6) possibly encoding α class CAs (carbonic anhydrase). Real-time RT-PCR analysis revealed the temporal expression pattern of each gene, as well as changes in expression levels under different atmospheric conditions (stress). Cah-3 and cah-4 showed the highest levels of transcript accumulation, while most genes responded to the stress conditions. Yeast complementation showed that cah-3 was able to complement the function of Saccharomyces cerevisiae CA (NCE103) in vivo. Recombinant CAH-3, CAH-4a and CAH-5 enzymes, expressed in Escherichia coli were used for in vitro measurement of CA activity. However, in vitro activity was only detectable for CAH-4a. RNAi by feeding was performed on wild-type C. elegans for all genes. The worms were examined for a visible phenotype under normal and stress conditions (pH, CO(2)/O(2)). Silencing cah-3 and cah-4 may reduce the life-span of the worms (at 22 °C).

Oomycetes are a group of eukaryotic organisms that includes many important pathogens of animals and plants. Within this group, the Haptoglossa genus is characterised by the presence of specialised gun cells carrying a harpoon-like infection apparatus. While several Haptoglossa pathogens have been morphologically described, there are currently no host systems developed to study the infection process or host responses in the lab. In this study, we report that Haptoglossa species are potent natural pathogens of Caenorhabditis nematodes. Using electron microscopy, we characterise the infection process in C. elegans and demonstrate that the oomycete causes excessive tissue degradation upon entry in the body cavity, whilst leaving the host cuticle intact. We also report that the host transcriptional response to Haptoglossa infection shares similarities with the response against the oomycete Myzocytiopsis humicola, a key example of which is the induction of chitinase-like (chil) genes in the hypodermis. We demonstrate that this shared feature of the host response can be mounted by pathogen detection without any infection, as previously shown for M. humicola. These results highlight similarities in the nematode immune response to natural infection by phylogenetically distinct oomycetes.

The worm appears to be robust to this form of (pulsed) radiation, at least under the exposure conditions used.