Mono-specific algal diets shape microbial networking in the gut of the sea urchin Tripneustes gratilla elatensis

The ability of algivorous sea urchins to gain energy from diets made up of a singlealgal species makes them favorable for the study of diet related changes in the gutmicrobial network. In order to ascertain whether changes are led by specificmicrobes in the assembly, we compared individuals' niche breadth, associations,and centrality in the networks of the three major regions in the gut of seaurchin Tripneustes gratilla elatensis fed either Ulva fasciata or Gracilariaconferta, or when fed algal-free pelleted feed. Dietary Ulva fasciata inducedunique microbes and associations which formed a denser and highly connectednetwork while the pelleted feed, which lacks any marine footprint, resulted in amuch lower connectivity between nodes with fragile chain-associations and greatercompetition on available resources. Among the core or hub microbes in the gut weidentified Bacteriodetes, and Firmicutes as the keystone taxa with their persistentoccurrence in the different niches. The former revealed high strain variability andassumed to rapidly evolve in the gut via spreading of new strains to unique nichesin which they are central microbes in the local network. When fed different diets,various strains of Bacteroidetes and Spirochaetes maintained communityconnectivity as central hub nodes while other strains were determined as drivermicrobes that rewired the network under particular diet regimes via changes in ownassociations, associating microbes and centrality.