The planctomycete Stieleria maiorica Mal15^T employs stieleriacines to alter the species composition in marine biofilms

Bacterial strains of the phylum Planctomycetes occur ubiquitously, but are often found on surfaces of aquatic phototrophs, e.g. alga. Despite slower growth, planctomycetes are not outcompeted by faster-growing bacteria in biofilms on such surfaces; however, strategies allowing them to compensate for slower growth have not yet been investigated. Here, we identified stieleriacines, a class of N-acylated tyrosines produced by the novel planctomycete Stieleria maiorica Mal15^T, and analysed their effects on growth of the producing strain and bacterial species likely co-occurring with strain Mal15^T. Stieleriacines reduced the lag phase of Mal15^T and either stimulated or inhibited biofilm formation of two bacterial competitors, indicating that Mal15^T employs stieleriacines to specifically alter microbial biofilm composition. The genetic organisation of the putative stieleriacine biosynthetic cluster in strain Mal15^T points towards a functional link of stieleriacine biosynthesis to exopolysaccharide-associated protein sorting and biofilm formation.