Genomic repertoire of Mameliella alba Ep20 associated with Symbiodinium from the endemic coral Mussismilia braziliensis

Abstract

Bacteria associated with Symbiodinium may exert relevant roles in the Symbiodinium and the coral host. The bacterial isolate Ep20 was obtained from cell suspensions of Symbiodinium retrieved from the endemic coral Mussismilia braziliensis (Abrolhos Bank, Brazil). Here we aimed to analyze the genomic repertoire of Ep20 to gain insights into its possible roles in the coral holobiont. Ep20 enhanced the growth of Symbiodinium under controlled laboratory conditions, possibly through nitrogen fixation and vitamin production. The genome of Ep20 contains 5.5 Mbp (65% G + C content), 5397 genes, 53 tRNAs, and four rRNAs. Ep20 was identified as Mameliella alba, a member of the Roseobacter Clade Bacteria (RCB, Alphaproteobacteria). The genomic repertoire of Ep20 includes genes responsible for i. Aerobic Anoxygenic Photosynthesis (AAP), ii. Cofactors and vitamins (B12), iii. Gene Transfer Agents (GTAs), iv. Dimethylsulfoniopropionate (DMSP) metabolism, v. Carbon and Nitrogen fixation, and vi. Secondary metabolites (e.g., Terpenes). The genomic attributes of Ep20 hint at a possible mutualistic interaction with Symbiodinium, both in the free-living and in the coral holobiont lifestyles.