Naturally occurring beneficial bacteria Vibrio alginolyticus X-2 protects seaweed from bleaching disease

Microbiome manipulation is gaining fresh attention as a way to mitigate diseases in aquaculture. The commercially farmed seaweed <em>Saccharina japonica</em> suffers from a bacterial induced bleaching disease that has major implications for the reliable supply of healthy sporelings. Here, we identify a beneficial bacterium, <em>Vibrio alginolyticus</em> X-2 that significantly decreases bleaching disease risk. By combining infection assays and multi-omic analyses, we provide evidence to suggest that the underlying protection mechanisms of <em>V. alginolyticus</em> X-2 involves maintaining epibacterial communities, increasing the expression of <em>S. japonica</em> genes related to immune and stress protection pathways and stimulating betaine concentrations in <em>S. japonica </em>holoboints. Thus, <em>V. alginolyticus</em> X-2 can elicit a suite of microbial and host responses to mitigate the bleaching disease. Our study provided insights into disease control in farmed <em>S. japonica</em> though the application of beneficial bacterium.