<jats:title>Summary</jats:title><jats:p> <jats:italic>Pseudomonas putida</jats:italic> strain PCL1445 was isolated from roots of plants, grown on a site polluted with polycyclic aromatic hydrocarbons. PCL1445 produces biosurfactant activity at the end of the exponential growth phase. High‐performance liquid chromatography (HPLC) analysis of supernatant extracts of PCL1445 showed two peaks with surface‐tension reducing activity, tentatively assigned as biosurfactants putisolvin I and putisolvin II and was followed by structural analyses. A transposon mutant of PCL1445, strain PCL1436, which lacks the two surface‐active peaks appeared to be mutated in an open reading frame (ORF) with amino acid homology to various lipopeptide synthetases. Structural analyses of the two biosurfactants of PCL1445 revealed that both are novel cyclic lipodepsipeptides with a hexanoic lipid chain connected to the N‐terminus of a 12‐amino‐acid peptide moiety, in which the C‐terminal carboxylic acid group forms an ester with the hydroxyl side‐chain of Ser9. The difference between the two structures is located in the second amino acid from the C‐terminus, being valine for putisolvin I, and leucine/isoleucine for putisolvin II. We show that these novel compounds lower the surface tension and influence the biofilm development on polyvinyl chloride (PVC). Biofilm formation of the bio‐synthetic mutant PCL1436 was strongly increased containing more cells, which formed aggregates earlier as compared with wild‐type PCL1445 biofilms. Using purified putisolvin I and II it was shown that biofilm formation of different <jats:italic>Pseudomonas</jats:italic> strains was inhibited and most interestingly, that both putisolvins are also able to break down existing <jats:italic>Pseudomonas</jats:italic> biofilms.