0 (approximately 106 CFU mL−1 for all strains), and incubated on a platform shaker (200 r.p.m.) at 28 °C for 24 h or 1 week. To quantify flocculation, we modified a protocol described previously (Madi Epacadostat & Henis, 1989; Burdman et al., 1998). Briefly, 1 mL of sample was subjected to mild sonication using a Branson Digital Sonifer Model 102C equipped with a 3.2 mm tapered micro tip. Settings for sonication included sonic pulses of 2 s on and 2 s off, with the amplitude set at 10%. The percentage of flocculation

was calculated by (ODa−ODb/ODa) × 100, where ODa is the OD after sonication and ODb the OD before sonication. AFM samples were prepared as described, with slight modifications (Doktycz Ceritinib et al., 2003). Briefly, 1-mL aliquots of bacteria were harvested by centrifugation (6000 g) after 24 h or 1 week of growth. Cells were resuspended in 100 μL dH2O and then deposited on a freshly cleaved mica surface. Samples were air-dried 8–24 h before imaging with a PicoPlus atomic force microscope (Agilent Technologies, Tempe, AZ) using a 100 μm multipurpose scanner. The instrument was operated in the contact mode at 512 pixels per line scan with speeds ranging from 0.5 to 1.0 Hz. A Veeco MLCT-E cantilever with a nominal spring constant of

0.5 N m−1 was used for imaging. For all samples, first-order flattened topography and deflection scans were acquired with sizes ranging from 1.5 to 75 μm. Strains were grown in 5 mL cultures as described above. After 24 h, cells were stained with Syto61 2-hydroxyphytanoyl-CoA lyase (Invitrogen) following the manufacturer’s instructions and resuspended in 200 μL phosphate-buffered

saline (PBS) (pH 7.4). Fluorescein isothiocyanate (FITC)-conjugated lentil (LcH; Sigma #L9262) or lima bean lectins (LBL; Sigma #L0264) were added at a final concentration of 50 μg mL−1. The cells were incubated at room temperature with shaking for 20 min, harvested at 8000 r.p.m., and washed with PBS. A Leica TCS SP2 scanning confocal microscope was used for image acquisition. imagej was used for image analysis. An aggregation bioassay described previously (Burdman et al., 1999, 2000a) was used to assess the roles of d-glucose and l-arabinose in flocculation. Briefly, all strains were grown in flocculation medium or in MMAB. After 24 h, flocculating cultures were sonicated for 20 s and then centrifuged (16 000 g, 2min). The supernatant was then added to cells grown in MMAB (nonflocculating) along with 0.05, 0.1, or 0.5 M concentrations of d-glucose or l-arabinose. The cultures were incubated at 28 °C with shaking for 3–4 h. Flocculation was quantified using the protocol described above. Lipopolysaccharides was extracted from all strains grown in TY and flocculation medium at 24 h and 1 week using an lipopolysaccharides extraction Kit (Intron Biotechnology) following the manufacturer’s instructions.