Figure 7. Morphological and physiological characteristics of biofilms formed by B. plantarii exposed to tropolone or carot-4-en-9,10-diol.

(A) General state of B. plantarii biofilm formation after a 48 h incubation in PDB containing 200 µM exogenous tropolone only (top, right panel), 200 µM exogenous tropolone plus 200 µM carot-4-en-9,10-diol (bottom, left panel), 200 µM carot-4-en-9,10-diol (bottom, right panel), and in PDB containing neither exogenous tropolone nor carot-4-en-9,10-diol as control (top, left panel). The microscopic observation was done with a 10× objective lens, after the cells were stained by a crystal violet. (B) Three dimensional structures of representative cell aggregates in each treatment after 48 h incubation were also observed under a phase contrast mode, with the same relative positions of each panel with that of A. Red arrows indicate the biofilm induced by tropolone, while yellow arrows indicates the biofilm induced by carot-4-en-9,10-diol. (C) Comparison of matrix of the biofilm formed by B. plantarii incubated for 96 h with endogenous tropolone (top panel, control) or 20 µM carot-4-en-9,10-diol (bottom panel). Black arrow indicates the typical fibrous matrix.