Samples were electrophoresed at 150 V for 1 h. Gels were silver stained as described (Kittelberger & Hilbink, 1993). Consistent with previous work, we observed differences in the flocculation behavior of A. brasilense strains deficient in CheA1 and CheY1 compared with wild-type cells (Table 1). At 24 h, aggregative structures and flocs were visible for the Che1 pathway

mutant strains AB101 (ΔcheA1) and AB102 (ΔcheY1), but were not seen in the wild-type cultures at this time point. The amount of flocculation relative to planktonic cells for AB101 and AB102 was increased after RGFP966 manufacturer 1 week of incubation (Table 1). Flocculation was significant for the wild-type culture after 1 week of incubation (Table 1). All strains had similar motility before flocculation, and all strains lost motility after significant flocculation occurred, in agreement with previous findings (Burdman et al., 1998; Pereg Gerk et al., 2000; Bible et al., 2008). Taken together, these data are consistent with earlier findings that AB101 and AB102 flocculate earlier than the wild-type strain (Bible et al., 2008). Examination of AFM images revealed that the extracellular matrix of AB101 (ΔcheA1) and AB102 (ΔcheY1) learn more contained fibrillar material at 24 h (Fig. 1c

and d and Supporting Information, Fig. S1). The extracellular matrix of AB101 (ΔcheA1) and AB102 (ΔcheY1) appeared as a ridged structure on the surface of cells with fibrils protruding from the cells (Fig. 1c and d, Fig. S1). In contrast, the extracellular material surrounding cells of the nonflocculating wild-type strain appeared to be smooth and globular at 24 h (Fig. 1a). Numerous high-resolution scans of wild-type nonflocculating cells failed to reveal fibrillar material (Fig. 1a and data not shown). After 1 week, however, why fibrillar material was observed for flocculating wild-type cells (Fig. 1b). Despite the apparent similarity of the macroscopic flocculation phenotype of the mutant strains, analyses of AFM topography and deflection images revealed a dissimilarity in the organizational pattern of the aggregating cells (Figs

2 and S2). The most striking difference was observed in comparing the extracellular material of AB102 (ΔcheY1) with that of AB101 (ΔcheA1) or wild-type cells. A network of extracellular material is visible between the AB102 (ΔcheY1) cells as early as 24 h (data not shown) and it becomes more distinct after 1 week (Fig. 2c). Line scans across the flocs indicate that AB102 (ΔcheY1) cells are embedded in a matrix that spans approximately 400 nm between cells (Fig. 2f). This tight organization is not observed in flocs formed by AB101 (ΔcheA1) (Fig. 2b). In this strain, as well as in flocculating wild-type cells, individual cells are distinctly defined within the flocs and no obvious features are observed between the cells (Fig.