The human body is colonized by microorganisms of diverse phylogenetic origins, principally bacteria, archaea, eukaryote, and viruses. In health, specific microbes exist in a symbiotic relationship with their human host, where they contribute essential vitamins and nutrients, prime the human immune system to recognize “non-self” antigens, and produce useful anti-inflammatory compounds that deter disease-causing microbes.

Non-protein-coding RNAs (ncRNAs) are expressed in viruses, archaea, prokaryotes and eukaryotes. They fulfil vital roles in the regulation of chromatin architecture, epigenetic memory, transcription, RNA splicing, editing and turnover. To date, at least 18 distinct types of ncRNA have been identified, which are classified according to their size, function, subcellular localization and target specificity.