Pseudochelin A was dissolved in DMSO to stock concentrations of 1.7 and 5 mg/mL. The stock solutions were diluted to final concentrations of 100 and 34 μg/mL, respectively, by mixing 2 μL of each solution with 98 μL of M63 liquid broth with seawater (see Table ) in 96-well plates in triplicates. Overnight cultures of the strains were grown in LB medium with artificial seawater and diluted to a starting OD600 of 0.01 in M63 liquid broth with seawater and 98 μL was transferred to each well, including solvent controls. Inoculated plates were incubated in a static incubator for 40 to 48 h at 30 °C. Bacterial growth was measured at 600 nm to ascertain whether the fractions were antibacterial and then adhered biofilms were stained with 0.1% (wt/vol) crystal violet (aq) and placed on an orbital shaker at low speed for 30 min. Planktonic cells were washed with DI water, the plates were dried (30 -60 min) at rt and then the crystal violet bound biofilms were solubilized using 130 μL of 30% acetic acid (aq). The solubilized material was transferred to new 96-well plates and absorbances (595 nm) measured. Raw absorbance readings were normalized to a vehicle control (negative control).