Metagenomic and metabolomic analysis of the effect of bleaching on unsaturated fatty acid synthesis pathways in coral symbionts

Abstract

Unsaturated fatty acids (UFAs) are known to play a vital role in regulating stress resistance and metabolism in corals. Nevertheless, a comprehensive understanding of the microbial and functional composition of the UFA synthesis pathway (UFASP) remains lacking. This study employed metagenome and metabolome to investigate the microbial community, function, and metabolic response of UFASP in reef-building corals inhabiting the Nansha Islands. Our findings revealed significantly higher diversity for the UFASP microbe in bleached corals compared to unbleached corals. Furthermore, principal coordinates analysis (PCoA) and taxonomy assessments exhibited notable distinctions in the microbe between the two coral states. Notably, the dominant microorganisms involved in UFASP were Dinophyceae, Sordariomycetes, Ulvophyceae, and Chlorophyceae. Bleaching resulted in a considerable increase in fungal abundance within coral symbionts. A total of 12 KEGG Orthology (KO) were identified in UFASP, with PCoA analysis indicating significant differences in their abundance between bleached and unbleached corals. UFASP's beta-Oxidation module exhibited reduced abundance in bleached corals. Contribution analysis highlighted the participation of Symbiodiniaceae, Ascomycota, Chlorophyta, Proteobacteria, and Actinobacteria in UFASP. Notably, Symbiodiniaceae and Ascomycota were the major contributors to two UFASP modules, with the latter displaying greater involvement in bleached corals. Furthermore, significant differences in n3 and n6-family metabolites were observed between bleached and unbleached corals. Notably, bleaching induced a reduction in metabolites of Symbiodiniaceae, while an increase in the multiple UFAs abundance was detected in bleached corals. These findings suggest that bleaching-induced alterations coral symbionts composition directly impact the functionality of UFASP, ultimately affecting the corals' capacity to adapt to stress.

Keywords: Bleaching; Metagenome; Microbial community; Unsaturated fatty acids synthesis pathway; Untargeted metabolome.