A Trojan horse mechanism of bacterial pathogenesis against nematodes

Abstract

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. nematocidaattractant 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 M ost model organisms, such as the yeast Saccharomyces cerevisiae, the slime mold Dictyostelium discoideum, the mouseear cress plant Arabidopsis thaliana, the common fruit fly Drosophila melanogaster, and the nematode Caenorhabditis elegans, can be infected by microbes, including certain human-pathogenic bacteria (1). For several reasons, C. elegans is an attractive model organism to study host-pathogen interactions: It has simple growth requirements, a short generation time, a well-defined developmental process with invariant cell lineage sorting, a fully sequenced genome, and a suite of well-established genetic tools (2). Using C. elegans as a model, scientists in the last few years have identified a diversity of physical, chemical, and biochemical features involved in microbial pathogenesis (3). For example, Brevibacillus laterosporus secretes extracellular proteases that damage nematode cuticle, and Bacillus thuringiensis produces toxic crystal proteins that disrupt host cellular functions (4, 5). The common humanpathogenic bacterium Pseudomonas aeruginosa kills C. elegans with quorum-sensing controlled-virulence factors (6) and cyanide (7). Several other human pathogens such as the Gram-negative bacteria Burkholderia pseudomallei and Serratia marcescens and the Gram-positive bacteria Enterococcus faecalis, Streptococcus pyogenes, and Staphylococcus aureus also are reported to have nematoxic activities via a neuromuscular endotoxin, a cytolysin, two extracellular proteases (gelatinase and serine protease), and several other toxins (8-12). In S. aureus, several virulence determinants known to be important in mammalian pathogenesis, including the quorum-sensing global virulence regulatory system agr and the global virulence regulator sarA, the alternative sigma factor B, α-hemolysin, and the V8 serine protease, are all required for full pathogenicity against nematode...

Hydrolysis of aromatic β-glucosides by non-pathogenic bacteria confers a chemical weapon against predators

“…The results reported here shed light on one such strategy-release of toxic aromatic compounds by the hydrolysis of b-glucosides by members of Enterobacteriaceae. In contrast to the antipredatory actions of pathogenic bacteria that have evolved specific tools such as extracellular proteases targeted against predators [21], our studies involved non-pathogenic bacteria that are armed only with genes that enable the uptake and hydrolysis of aromatic b-glucosides. The energy investment is minimal for the bacterium and a part of it could be derived from the glucose generated during the hydrolysis of b-glucosides.…”

Chemotaxis of Caenorhabditis elegans toward volatile organic compounds from Stropharia rugosoannulata induced by amino acids

“…All these compounds are known attractants for C. elegans (Matsumori et al, 1989;Bargmann et al, 1993;Niu et al, 2010).…”

“…Bristol strain N2 was cultured on semi-liquid oat medium (10 g of oats, 6 ml of distilled water) at 28°C for 6 to 8 days. The cultured nematodes were grown to adulthood separated using the Baerman funnel technique, and distilled water suspension of the nematode was prepared as a working stock (Niu et al, 2010).…”

“…In the soil environment, microorganisms such as bacteria can produce diacetyl (butabediol) as attractants for nematodes (Zhang et al, 1997). Some bacteria such as the Bacillus nematocida B16 is capable of releasing a variety of food-like odors as attractants, including benzaldehyde, 2-heptanone, indole, naphthalene, 2, 5-dimethy-lanisole, benzyl benzoate and acetophenone, and these VOCs have shown potent nematode-attracting abilities (Niu et al, 2010). Monoson and Ranieri (1972) found that attractants for the nematode Aphelenchus avenae were related to trap formation of Arthrobotrys oligospora.…”

Feeding behaviour of Caenorhabditis elegans is an indicator of Pseudomonas aeruginosa PAO1 virulence

“…Binary assays have 56 also shown that C. elegans learns to avoid pathogenic bacteria, if the worms are exposed to the 57 pathogen prior to a binary choice feeding behaviour experiment (Zhang, Lu & Bargmann, 2005). 58Worms may be attracted to certain diffusible odorants and repelled by others (Bargmann, 59 Hartwieg & Horvitz, 1993; Schulenburg & Ewbank, 2007), however, Bacillus nematocida both 60 attracts and kills C. elegans, thereby acting as a nematode predator (Niu et al, 2010). C. elegans 61 feeding behaviour, sensing and decision making regarding food sources is complex and involves 62 multiple neural pathways (Schulenburg & Ewbank, 2007; Sengupta, 2013 Escherichia coli OP50 was used as a non-pathogenic food source for cultivating C. elegans.…”