Roseobacter enrichment early in life facilitates future colonization of Roseobacter bacteria and improves long-term survival against Vibrio aestuarianus in the Pacific oyster

Exposure to beneficial bacteria during early immune development may promote long-term survival against pathogens, known as "microbial education." As marine diseases intensify with ocean warming, methods to improve marine organisms robustness against disease will be valuable for mitigation. Here, we experimentally tested whether exposure to high temperature seawater, seawater enrichment with Roseobacter bacteria, or a combination of both during the first 24 hours of life enhances long-term survival of the Pacific oyster (Crassostrea gigas) against the widespread marine pathogen, Vibrio aestuarianus subsp. francensis, at high temperatures (24 {degrees}C). Exposure to high temperatures early in life did not improve future survival during disease challenges and caused high larval mortality. Conversely, Roseobacter enrichment during high temperature exposure resulted in a "microbial rescue effect," improving larval survival. We found that Roseobacter enrichment during the first 24 hours of life improved future survival against V. aestuarianus at high temperatures by up to [~]28% at 13 days post-fertilization (dpf) and [~]30% at 90 dpf. Ultimately, the supplemented Roseobacter species did not remain associated with the host microbiome but instead was replaced by a high abundance of other Roseobacter bacteria at 90 dpf. These findings suggest that early Roseobacter enrichment facilitates future colonization by other Roseobacter species, which may in turn protect against pathogenic V. aestuarianus, supporting the concept of microbial education in marine invertebrates and its potential use to combat marine diseases. ImportanceThis research identifies key aspects of early developmental processes in a marine invertebrate, Crassostrea gigas, and explores how these processes can be utilized to alter host-microbe interactions later in life.