The first host-associated anaerobic isolate of Psychrilyobacter provides insights into its potential roles in the abalone gut

Gut bacteria are essential to their hosts, but few studies have focused on marine animals. Psychrilyobacter is frequently related to various marine animals, but the relationship with host remains unknown due to lack of host-associated isolate or genomic information. Here, we combined of high-throughput sequencing, isolating and genomic analyses to uncover its potential role in host abalone. The high-throughput sequencing and literature compiling results indicated that Psychrilyobacter is widely distributed in marine and terrestrial ecosystems with both host-associated and free-living lifestyles. It showed a strong preference for the guts of marine invertebrates, especially abalone, which generally persisted with high relative abundances. By mimicking the gut inner environment for enrichment, the first host-related pure culture of Psychrilyobacter was isolated from the abalone intestine. Phylogenetic, physiological and biochemical characterizations suggested that it represents a novel species named Psychrilyobacter haliotis B1. Carbohydrate utilization experiments and genomic evidence indicated that B1 is good at fermenting diverse host-food-related monosaccharides and disaccharides but not polysaccharides, implying its critical roles in downstream fermentation instead of upstream food degradation in the gut. Furthermore, this strain showed potential to colonize the gut and benefit the host via different strategies, such as short-chain fatty acids (SCFAs) generation by fermenting carbohydrates and amino acids, and the production of diverse vitamins and antibiotics to support the host growth and antipathogenicity. To our knowledge, strain B1 represents the first host-related pure culture of Psychrilyobacter, acting as a potential probiotic gut anaerobe dominating in diverse marine invertebrates. ImportancePsychrilyobacter is a globally distributing bacterial genus and with an inhabiting preference for guts of marine invertebrates. Due to the difficulty of cultivation and the limited genomic information, its role in host remains largely unknown. We isolated the first host-associated Psychrilyobacter species from abalone gut and uncovered its functional potentials to the host through different mechanisms. Our findings provide some insights into the understanding of host-microbe interactions on a core taxon with the marine invertebrates, and the isolate has an application prospect as a probiotic in protection of marine animals.