Editorial: C. elegans host-microbiome interactions: From medical to ecological and evolutionary model

Platforms for the Search for New Antimicrobial Agents Using In Vivo C. elegans Models

Despite the achievements brought about by high-throughput screening technologies, there is still a lack of effective platforms to be used to search for new antimicrobial drugs. The antimicrobial activity of compounds continues, for the most part, to be assessed mainly using in vitro pathogen cultures, a situation which does not make easy a detailed investigation of the molecular mechanisms underlying host-pathogen interactions. In vivo testing of promising compounds using chordate models is labor-intensive and expensive and, therefore, is used in preclinical studies of selected drug candidates but not in primary screening. This approach does not facilitate the selection of compounds with low organ toxicity and is not suitable for the identification of therapeutic compounds that affect virulence factors. The use of microscopic nematode C. elegans to model human infections is a promising approach that enables one to investigate the host-pathogen interaction and identify anti-infective compounds with new mechanisms of action.

Distinct members of the Caenorhabditis elegans CeMbio reference microbiota exert cryptic virulence that is masked by host defense

Microbiotas are complex microbial communities that colonize specific niches in the host and provide essential organismal functions that are important in health and disease. Understanding the ability of each distinct community member to promote or impair host health, alone or in the context of the community, is imperative for understanding how differences in community structure affect host health and vice versa. Recently, a reference 12-member microbiota for the model organism Caenorhabditis elegans, known as CeMbio, was defined. Here, we show the differential ability of each CeMbio bacterial species to activate innate immunity through the conserved PMK-1/p38 MAPK, ACh-WNT, and HLH-30/TFEB pathways. Although distinct CeMbio members differed in their ability to activate the PMK-1/p38 pathway, the ability to do so did not correlate with bacterial-induced lifespan reduction in wild-type or immunodeficient animals. In contrast, most species activated HLH-30/TFEB and showed virulence toward hlh-30-deficient animals. These results suggest that the microbiota of C. elegans is rife with bacteria that can shorten the host's lifespan if host defense is compromised and that HLH-30/TFEB is a fundamental and key host protective factor.