The efficacy of tannic acid in controlling biofouling by Pseudomonas aeruginosa is dependent on nutrient conditions and bacterial density

• TA reduced biofilm in M9 and YNB medium at lower bacterial concentration.
• Organic nitrogen played an important role in the anti-biofilm efficacy of TA.
• Decrease in anti-biofilm efficacy of TA was observed in the presence of tannase.
• It was found that organic nitrogen limitation triggers tannase formation.

This study investigated the effect of tannic acid (TA) on biofilm formation by Pseudomonas aeruginosa PAO1 as a model organism. Here, we report that TA enhanced biofilm formation in M9 medium at a bacterial concentration of 0.1 (OD600) on different model surfaces such as: polystyrene microtiter plate, polypropylene tube and borosilicate glass tube. However, TA reduced biofilm formation by PAO1 in M9 and yeast nutrient broth (YNB) media at a bacterial concentration of 0.001 (OD600). Strikingly, TA reduced biofilm formation at a bacterial concentration of 0.01 (OD600) in YNB medium but increased biofilm formation in M9 medium. When yeast extract (10 g/l) was added to the M9 medium TA reduced biofilm formation (51.0%). These trends were confirmed qualitatively and quantitatively by confocal microscopy. In the presence of yeast extract, TA exhibited 89.0% biofilm biovolume reduction compared to the untreated control. When yeast extract, tryptone and l-arginine were added to M9 medium, TA showed anti-biofilm activity at all bacterial densities tested. When tannase was added, the anti-biofilm efficacy of TA decreased. Furthermore, organic nitrogen limitation triggered TA degradation in the cultures (P < 0.05), which in turn restored biofilm formation. These results suggest that bacterial density and nutritional conditions are critical to the anti-biofilm efficacy of TA against PAO1 and thus may explain differences in the literature regarding the effect of TA on biofilm formation.