the influence of trivalent and bivalent cations on biofilm properties:
aluminum chloride hexahydrate (97%; 26726139, Molekula GmbH), iron(III)
chloride anhydrous (I/1035/50, Fisher Scientific), zinc chloride (≥98%)
(29156.231, VWR International), calcium chloride dihydrate (≥99%;
C3306, Sigma-Aldrich). AlCl3, FeCl3, ZnCl2, and CaCl2 were dissolved in ultrapure water to
a concentration of 220 mM, and the pH was measured with a pH-meter
(WTW GmbH;
Using the FeCl3 solution as a reference, a control solution
with an identical pH was prepared with hydrochloric acid (1.09057,
Merck KGaA). In addition to the pH, the osmolality of the metal solutions
can also influence biofilm properties via water intake of the biofilm.
The osmolalities of the different solutions were measured with an
osmometer (Osmomat 3000, Gonotec GmbH). The osmolalities were determined
from a calibration curve established from solutions of sodium chloride
(39781.02, Serva Electrophoresis) (
the osmolality of the FeCl3 solution.