Diverse secondary metabolites are expressed in particle-associated and free-living microorganisms of the permanently anoxic Cariaco Basin

Secondary metabolites play essential roles in ecological interactions and nutrient acquisition, and are of interest for their potential uses in medicine and biotechnology. Under laboratory conditions the discovery of new compounds is hindered by low production, high rediscovery rates, and detection evasion. Genome mining for biosynthetic gene clusters (BGCs) is a popular approach to address these limitations, thereby uncovering often cryptic secondary metabolic potential. Marine systems are often underrepresented in bulk genome mining efforts; and habitats with unique physicochemical characteristics such as oxygen-depleted and anoxic water columns remain virtually unexplored regarding BGCs. Here, we use genome mining and differential gene expression analyses to show that redox potential and particle-associated vs. free-living lifestyles both influence the composition and production of secondary metabolites through the stratified water column of the Cariaco Basin, Venezuela. Microbiota, including understudied clades, such as Planctomycetota, encode and express a wide range of secondary metabolites in these anoxic/euxinic waters.