Abstract

Bacteria were the first inhabitants on earth, and worms one of the earliest animals. Their mutual adaptation points to a remarkable genetic plasticity, underlying rapidly evolving molecular and behavioral strategies for long-term survival. Behavioral adaptive responses require the active communication between bacteria and the animal's intestine. After their encounter the holobiont changes at many levels, including global transcriptomic and epigenetic adaptations. RNA is a likely mediator of these changes because it is a mobile molecule capable of messaging complex and precise information to distant targets and across generations. Caenorhabditis elegans and their commensal and pathogenic bacteria are a good model to study the components and dynamics of interspecies RNA communication in vivo and across generations. We focus on current research on extracellular RNA transport and uptake, and in putative ways in which exogenous RNA can affect global transcriptomic and epigenomic profiles in other species, highlighting its role in interspecies communication and memory. Some epigenetic effectors are sRNA-mediated which opens a complex landscape of possible pathways. We advocate the idea that the export, travel and import of small RNAs between bacteria and host is an active and targeted process, and there is increasing evidence that points in that direction. Some mechanistic proposals and future directions are outlined.