Like all macroorganisms, plants have to control bacterial biofilm formation on their surfaces. On the other hand, biofilms are highly tolerant against antimicrobial agents and other stresses. Consequently, biofilms are also involved in human chronic infectious diseases, which generates a strong demand for anti-biofilm agents. Therefore, we systematically explored major plant flavonoids as putative antibiofilm agents using different types of biofilms produced by Gram-negative and Gram-positive bacteria. In Escherichia coli macrocolony biofilms, the flavone luteolin and the flavonols myricetin, morin and quercetin were found to strongly reduce the extracellular matrix. These agents directly inhibit the assembly of amyloid curli fibres by driving CsgA subunits into an off-pathway leading to SDS-insoluble oligomers. In addition, they can interfere with cellulose production by still unknown mechanisms. Submerged biofilm formation, however, is hardly affected. Moreover, the same flavonoids tend to stimulate macrocolony and submerged biofilm formation by Pseudomonas aeruginosa. For Bacillus subtilis, the flavonone naringenin and the chalcone phloretin were found to inhibit growth. Thus, plant flavonoids are not general anti-biofilm compounds but show speciesspecific effects. However, based on their strong and direct anti-amyloidogenic activities, distinct plant flavonoids may provide an attractive strategy to specifically combat amyloid-based biofilms of some relevant pathogens.

For centuries, across West Africa, plants have been used extensively not only in traditional medicine but also for dyeing cloth. Examples are the use of the bark of Terminalia laxiflora, the root of Cochlospermum tinctorium and the pods of Acacia nilotica, which together form the vegetable basis of a complex natural colorant produced by the hunters of the Marka-Dafing community in the Mouhoun region of north-western Burkina Faso. This colorant, known as vouwo and used by the hunters to dye a hunting and ceremonial shirt called a donso dileke (hunter shirt), is prepared by adding the plant elements to soil and iron ore in water. This mixture of ingredients then undergoes a long process of fermentation, whereby an essential role is played by certain bacteria present in the mud. This paper examines the use of extracts of the pods of A. nilotica to counteract certain counterproductive bacteria that under non-optimal conditions may proliferate in the dyeing jar, forming thick biofilms and inhibiting the dyeing process. Besides showing some previously studied antibacterial activity, extracts of A. nilotica pods have also been found to interfere efficiently with the biofilm formation of these bacteria. By suppressing the disruptive bacteria, A. nilotica seems to support the proliferation and desired activity of the bacteria that contribute to the coloring of the textile (mainly anaerobic producers of iron sulphide). While extensive research has been carried out on the phytochemistry of traditional medicinal plants, in this ongoing study, the authors investigate the role of A. nilotica in traditional fermentative cloth dyeing by looking into aspects of the microbiome that develops during the dyeing of the hunter shirt. The interdisciplinary approach of this study to the complex roles of natural dyes combines extensive anthropological field research with microbiological methods.