Lactobacillus zeae Protects Caenorhabditis elegans from Enterotoxigenic Escherichia coli-Caused Death by Inhibiting Enterotoxin Gene Expression of the Pathogen

Abstract

BackgroundThe nematode Caenorhabditis elegans has become increasingly used for screening antimicrobials and probiotics for pathogen control. It also provides a useful tool for studying microbe-host interactions. This study has established a C. elegans life-span assay to preselect probiotic bacteria for controlling K88+ enterotoxigenic Escherichia coli (ETEC), a pathogen causing pig diarrhea, and has determined a potential mechanism underlying the protection provided by Lactobacillus.Methodology/Principal FindingsLife-span of C. elegans was used to measure the response of worms to ETEC infection and protection provided by lactic acid-producing bacteria (LAB). Among 13 LAB isolates that varied in their ability to protect C. elegans from death induced by ETEC strain JG280, Lactobacillus zeae LB1 offered the highest level of protection (86%). The treatment with Lactobacillus did not reduce ETEC JG280 colonization in the nematode intestine. Feeding E. coli strain JFF4 (K88+ but lacking enterotoxin genes of estA, estB, and elt) did not cause death of worms. There was a significant increase in gene expression of estA, estB, and elt during ETEC JG280 infection, which was remarkably inhibited by isolate LB1. The clone with either estA or estB expressed in E. coli DH5α was as effective as ETEC JG280 in killing the nematode. However, the elt clone killed only approximately 40% of worms. The killing by the clones could also be prevented by isolate LB1. The same isolate only partially inhibited the gene expression of enterotoxins in both ETEC JG280 and E. coli DH5α in-vitro.Conclusions/SignificanceThe established life-span assay can be used for studies of probiotics to control ETEC (for effective selection and mechanistic studies). Heat-stable enterotoxins appeared to be the main factors responsible for the death of C. elegans. Inhibition of ETEC enterotoxin production, rather than interference of its intestinal colonization, appears to be the mechanism of protection offered by Lactobacillus.

FIT2 is a lipid phosphate phosphatase crucial for endoplasmic reticulum homeostasis

“…Consistent with its expression pattern, FIT2 is important in LD formation and lipid storage (Choudhary et al, 2015;Kadereit et al, 2008) in all model systems investigated, including yeast, fish, worms and mice (Choudhary et al, 2015;Kadereit et al, 2008). In Caenorhabditis elegans, deletion of the FIT2 orthologue is not compatible with life (Choudhary et al, 2015). The global postnatal knockout of FIT2 in mice also results in lethality due to catastrophic effects on the small intestine (Goh et al, 2015).…”

“…FIT2 was originally identified as a transcript that was induced after treatment with PPARa agonist in mice (Kadereit et al, 2008). Consistent with its expression pattern, FIT2 is important in LD formation and lipid storage (Choudhary et al, 2015;Kadereit et al, 2008) in all model systems investigated, including yeast, fish, worms and mice (Choudhary et al, 2015;Kadereit et al, 2008). In Caenorhabditis elegans, deletion of the FIT2 orthologue is not compatible with life (Choudhary et al, 2015).…”

“…Supporting this, scs3D cells are auxotrophic for inositol, a condition exacerbated by addition of choline, both key metabolites in phospholipid synthesis (Hosaka et al, 1994). Intriguingly, Scs3 and Yft2 have been implicated as crucial determinants for the directionality of LD budding (Choudhary et al, 2015). These previous observations led to a model in which FIT2 is predominantly a structural protein, with neutral lipid binding, that may be involved in the partitioning of lipids for LD formation and budding (Gross et al, 2011;Kadereit et al, 2008).…”

“…Lipid droplet (LD) formation is an important function of the ER (Choudhary et al, 2015;Jacquier et al, 2011;Kassan et al, 2013). These cytosolic organelles serve as cellular reservoirs for neutral lipids that are used for membranes or generating metabolic energy (Walther and Farese, 2012).…”

Are nematodes a missing link in the confounded ecology of the entomopathogen Bacillus thuringiensis?

“…In addition to these Cry proteins, thuringiensin, chitinase [45], and a metalloproteinase from B. thuringiensis are also toxic to nematodes [46,47]. Genes encoding nematicidal factors, including lantibiotics [48], enterotoxins [49], hemolysins [50], and proteases [51], are also commonly present in the genome of B. thuringiensis and are mostly controlled by the transcriptional activator PlcR [52][53][54]. There is also compelling evidence that B. thuringiensis infects, germinates, and replicates inside Caenorhabditis elegans [55][56][57].…”