Bacteria–bacteria interactions within the microbiota of the ancestral metazoan Hydra contribute to fungal resistance

Abstract

Epithelial surfaces of most animals are colonized by diverse microbial communities. Although it is generally agreed that commensal bacteria can serve beneficial functions, the processes involved are poorly understood. Here we report that in the basal metazoan Hydra, ectodermal epithelial cells are covered with a multilayered glycocalyx that provides a habitat for a distinctive microbial community. Removing this epithelial microbiota results in lethal infection by the filamentous fungus Fusarium sp. Restoring the complex microbiota in gnotobiotic polyps prevents pathogen infection. Although mono-associations with distinct members of the microbiota fail to provide full protection, additive and synergistic interactions of commensal bacteria are contributing to full fungal resistance. Our results highlight the importance of resident microbiota diversity as a protective factor against pathogen infections. Besides revealing insights into the in vivo function of commensal microbes in Hydra, our findings indicate that interactions among commensal bacteria are essential to inhibit pathogen infection.

Antimicrobial effectors in the nematode Caenorhabditis elegans : an outgroup to the Arthropoda

“…This nematode seems to contain a rich microbial flora [83,98,99], yet the exact species composition and functions of the microbiome of natural C. elegans isolates have not yet been published. The production of antimicrobial compounds, for example bacteriocins or specific anti-fungal proteins, is known for microbiota members of various host taxa, ranging for example from Hydra polyps [100] to humans (e.g. [101]).…”

Skin bacterial diversity of Panamanian frogs is associated with host susceptibility and presence of Batrachochytrium dendrobatidis

“…It is becoming clear that in many systems (e.g. plants, Hydra, corals, amphibians and humans) bacterial symbiotic communities play an important role in protecting hosts from pathogens (Rosenberg et al, 2007;Harris et al, 2009;Innerebner et al, 2011;Khosravi and Mazmanian, 2013;Fraune et al, 2014). Conversely, the diversity and structure of symbiotic bacterial communities can be altered following pathogen infection (Round and Mazmanian, 2009;Cárdenas et al, 2012;Fierer et al, 2012;Jani and Briggs, 2014).…”

Using Nematostella vectensis to Study the Interactions between Genome, Epigenome, and Bacteria in a Changing Environment

“…These changes can arise through changes in the relative abundance of associated microorganisms, the introduction of new members, genetic variation in the microorganisms or horizontal gene transfer. Plasticity in bacterial colonization can contribute to thermotolerance of the holobiont (Dunbar et al, 2007), prevent growth of external pathogens (Woodhams et al, 2007;Fraune et al, 2014) or determine host body color (Tsuchida et al, 2010). Therefore, it can be hypothesized that molecular communications between host and microbe select for a core microbiota in a given host species which contributes to adaptation when the environment changes.…”

“…Colonizing bacteria are also a vital component of cnidarian holobionts (Lesser et al, 2004;Fiore et al, 2010;Fraune et al, 2014). In N. vectensis bacterial colonization is characterized by a stable associated bacterial community, which is dynamic but highly conserved in response to host development.…”

“…For instance if the silencing of a gene by methylation is suspected to have a role in acclimation to high temperatures, this could be tested by silencing this gene by other means. The role of bacteria could be tested by creating germ-free animals and re-infecting these animals with specific strains or combination of stains to determine functional relationships between the anemone and its microbial community (Fraune et al, 2014). Hypotheses pertaining to the interactions between these two types of mechanisms could then be tested by combining these two types of experimental manipulations (e.g., addition of one bacterial species plus repression on one methylated gene in germ-free anemone cultured at high temperature) to discern combinatorial effects that may be additive, synergistic, or antagonistic.…”