The Roseobacter group is a widespread marine bacterial group and some species produce the bioactive compound, tropodithietic acid (TDA). In vitro, TDA is a broad-spectrum antibiotic affecting several prokaryotes, including fish and human pathogenic Vibrio spp.. A mode of action has been proposed in Escherichia coli, but little is known about the impact of TDA on other, marine bacteria at in situ concentrations. The purpose of this study is to investigate how sub-lethal levels of TDA affect Vibrio vulnificus using a transcriptomics approach.