Novel technologies uncover novel ‘anti’-microbial peptides in Hydra shaping the species-specific microbiome

Abstract

The freshwater polyp Hydra uses an elaborate innate immune machinery to maintain its specific microbiome. Major components of this toolkit are conserved Toll-like receptor (TLR)-mediated immune pathways and species-specific antimicrobial peptides (AMPs). Our study harnesses advanced technologies, such as high-throughput sequencing and machine learning, to uncover a high complexity of the Hydra 's AMPs repertoire. Functional analysis reveals that these AMPs are specific against diverse members of the Hydra microbiome and expressed in a spatially controlled pattern. Notably, in the outer epithelial layer, AMPs are produced mainly in the neurons. The neuron-derived AMPs are secreted directly into the glycocalyx, the habitat for symbiotic bacteria, and display high selectivity and spatial restriction of expression. In the endodermal layer, in contrast, endodermal epithelial cells produce an abundance of different AMPs including members of the arminin and hydramacin families, while gland cells secrete kazal-type protease inhibitors. Since the endodermal layer lines the gastric cavity devoid of symbiotic bacteria, we assume that endodermally secreted AMPs protect the gastric cavity from intruding pathogens. In conclusion, Hydra employs a complex set of AMPs expressed in distinct tissue layers and cell types to combat pathogens and to maintain a stable spatially organized microbiome. This article is part of the theme issue ‘Sculpting the microbiome: how host factors determine and respond to microbial colonization’.

Sculpting the microbiome

“…The next article by Klimovich & Bosch [ 5 ] uses a mix of functional analysis, single-cell RNA sequencing and machine learning to detail the complexity of antimicrobial peptide contributions to microbiome maintenance in Hydra jellyfish. This unique model system allows detailed study of the gastric cavity in an organism with a functional and manipulable nervous system.…”

“…This unique model system allows detailed study of the gastric cavity in an organism with a functional and manipulable nervous system. Klimovich & Bosch [ 5 ] reveal how different endo- or ectodermal cell types produce varying complements of immune effectors, taking advantage of modern techniques. They discuss the actions of these antimicrobial peptides and Kazal-type protease inhibitors in the context of microbiome control.…”