Trojan horses and other dirty tricks

Caenorhabditis elegans Nematode worms burrowing through the soil encounter thousands of species of bacteria, but how do they find safe food choices from this vast buffet? A major part of the nematode’s ability to distinguish between food sources relies on a sophisticated chemosensory system that enables it to sense and respond to a wide range of volatile and water-soluble chemicals. During the past decade, the roundworm Caenorhabditis elegans has become a popular model for the study of host/pathogen relationships, leading to a wealth of information about microbial virulence factors and host defense pathways. Although the complicated interactions between C. elegans and the many pathogens that it encounters in the soil have become clearer in recent years, there is still much to learn. What are the cues that worms use to detect food sources? How do worms choose which bacterial species to eat and which to leave alone? Once a pathogen is encountered, what are the microbial killing mechanisms and the nematode’s survival mechanisms? This paper provides a rare view of one C. elegans/pathogen relationship. It describes the signals Bacillus nematocida uses to attract C. elegans, the virulence factors it uses to kill worms from within, and the specific host proteins targeted.

A Trojan horse mechanism of bacterial pathogenesis against nematodes. (2010) PNAS USA 107 (38) 16631–16636
Understanding the mechanisms of host–pathogen interaction can provide crucial information for successfully manipulating their rela- tionships. 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.


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