FIG 4 .

Coexpression of a LuxR-type receptor from P. luteoviolacea 2ta16 activates high levels of violacein production in E. coli. (A) Schematic illustrating coexpression of candidate quorum-sensing receptors from P. luteoviolacea with pCAP05-vio2ta16 in E. coli BL21(DE3). (B) Quantification of violacein production in a coexpression experiment. Cultures were grown to an OD₆₀₀ of 0.5 to 0.6, induced with 100 μM IPTG, and incubated at 18°C with shaking for 24 h before extraction and violacein quantification by HPLC. Candidate regulators are on the x axis and ordered by similarity to CviR as determined by DELTA-BLAST, and putative response regulators are blue. The data plotted are the mean ± standard error of total production on the right y axis and fold change compared to the control on the left y axis (n = 3). Statistical significance was determined with a one-tailed Student t test (*, P < 0.01; ***, P < 0.0005). PLR7 was not expressed solubly in E. coli, as indicated by the red X. (C) Neighbor-joining phylogenetic tree of quorum-sensing receptors LuxR and CviR and homologs identified from P. luteoviolacea 2ta16 generated with Geneious 5.1.7. An alignment was generated with a Blosum62 cost matrix, and the tree was built with a Jukes-Cantor genetic distance model in Geneious Tree Builder.