5 g, proteose peptone 0.5 g, casamino acids 0.5 g, glucose check details 0.5 g, soluble starch 0.5 g, sodium pyruvate 0.3 g, K2HPO4 0.3 g, MgSO4·7H2O 0.05 g, agar 15 g in 1 L distilled water) plates and incubated at 25 °C for 20 h. The cells were then harvested from the filter

followed by resuspension in 1 mL PBS, and FCM analysis as specified below. For the microbial community, we spotted 5 μL of each isolate (OD600 ≈ 0.3–0.7) and 75 μL of donor strain (either P. putida or E. coli, prepared as described above) onto the filter, incubated and analyzed by FCM at the same conditions as for the single-strain matings. Controls with only donors or recipients were included. Flow cytometric enumeration of cells was carried out with a FACScalibur flow cytometer (Becton Dickinson, San Jose, CA) equipped with a 15 mW argon laser (488 nm). The following settings and voltages were used during analysis: forward scatter = E01, side scatter (SSC) = 350, and the fluorescent detectors FL1 (530/30 nm), FL2 (585/42 nm), FL3 (650/30 nm) were set at 510 V. A threshold was set on the SSC, and no compensation was used. All parameters

were on logarithmic mode. Samples were run at the ‘low’ flow rate setting for 1 min. All the samples were diluted in PBS before flow enumeration to assure optimal bacterial counts to 2000 events s−1. In part of the sample (100 μL), gfp-expression was induced by incubation in LB with 1 mM of isopropyl-b-D-1-thiogalactopyranoside SB431542 (IPTG, SIGMA) for 3 h at 30 °C (P. putida) and 37 °C (E. coli) to determine the number of donor cells (Musovic et al., 2006). To isolate and identify recipients from the E. coli-community mating, one subsample of each replicate of the cell extract was diluted to 1000 events s−1 to flow-sorted (MoFlo; DAKO) at a flow rate of 400–1000 events s−1, with an optimal setting of the sheath pressure of ca. 60 psi and drop drive frequency to ca. 95 kHz, using a 70-μm CytoNozzle tip on an enrichment sort option of single-mode per single drop envelope. Dilutions up to 10−3 were made from approximately

Thiamet G 70 000 cells of each replicate, and 100 μL of each dilution were plated on TSA plates supplemented with kanamycin, streptomycin (100 mg mL−1) and tetracycline (20 mg mL−1) and incubated at 25 °C for 2–5 days. Four green colonies of each replicate were selected for DNA extraction and identified by sequencing after the amplification of the 16S rRNA gene as described above. Data analysis was carried out with the cellquest software package. Two polygonal gates were defined in bivariate FL1 vs. FL2 to count for green cells and in bivariate SSC vs. FL2 density plot as a double check. All microcosmic experiments were carried out in triplicate. Standard deviations were calculated with Excel (Microsoft®). A Student’s t-test was applied and probabilities less than 0.05 were considered significant.