FIG 7.

Flow cytometry analysis of P_BAD and P_xut promoter-driven GFP expression in Pseudomonas species indicates increased leakiness and increased proportions of bacteria expressing GFP with an inducer. The expression of gfpmut3 from the two different promoters was measured by flow cytometry. Cultures were prepared in LB medium with an inducer (10 mM) and were grown at 30°C. Gray areas represent PA14 or Pf0-1 with no plasmid, used to determine background levels. Yellow peaks represent bacteria with pMQ578 or pMQ80 without an inducer, used to indicate leakiness. Blue (and green) peaks represent bacteria with pMQ578 or pMQ80 and with an inducer. The pMQ578 plasmid has P_xut-gfp, and pMQ80 has P_BAD-gfp. Xylose was used as an inducer for pMQ578, and arabinose was used for pMQ80. Levels of GFP fluorescence above those for bacteria without a plasmid were used to determine the positive cutoff (noted as GFP+); horizontal green bars indicate positive values. Results of a representative experiment are shown (n, ∼100,000 cells per group).