Within our analysis we mainly focused on those genes that are possibly linked to QS according to references. Those genes that were at least 10-fold down-regulated were included in Table 1. Among the genes significantly downregulated we identified the lasI, lasB, rhlI, hcnA and pqsA/B/C/D genes, thus including autoinducer synthesis genes for both AHLs as well as for the Pseudomonas quinolone signal. In addition a significant number of genes and ORFs were detected that had been linked to QS-phenotypes in PAO1 and that were less than 10-fold but at least 4-fold altered in their expression level. Altogether these were 80 genes/ORFs and among those we found the hcnB and hcnC genes involved in hydrogen cyanide synthesis, the aprD and aprE genes involved in alkaline protease secretion as well as lecB and lasA. Although the majority of the flagellar genes was not affected by bpiB09 expression, the fliC gene, encoding the major flagellin, was strongly repressed. Also the transcription of flgD, flgE and flgF was at least tenfold down regulated. Altogether, these findings supported the observations made with respect to the observed phenotypes of cells expressing the bpiB09 gene. Genes that were at least 10-fold induced were included in Table S3. Further our data also suggested that the overall expression of the synthesis genes of the different autoinducers was abolished or strongly down-regulated. Thus expression of bpiB09 in PAO1 clearly affects transcription of known QS-regulated genes and ORFs and has therefore strong impact on the physiology of this microbe. Sequence based WZ4002 EGFR/HER2 inhibitor classifications assign BpiB09 to the large superfamily of short-chain reductases. The SDR superfamily consists of over 47,000 variants, with residue identities of 20�C 30%. This superfamily of enzymes can be subclassified at a first level into 5 families based on chain lengths and conserved sequence motives. Based on those classifications, BpiB09 belongs to the so-called classical SDR family. The presence of an arginine in the Gly-motif and at the first position after the second beta strand assigns BpiB09 into subfamily cP3. BpiB09 was crystallized and a complete data set was collected to 2.4 A �� resolution at beamline X13 at EMBL Hamburg/DESY. Data collection and refinement VE-821 statistics are summarized in Table 2. The structure was solved by molecular replacement using PDB structure 2EHD as a template. BpiB09 assumes a typical Rossmann fold with a central beta sheet flanked by helices aA aB and aF on one side and aC, aD and aE on the other side. The strand topology is with a crossover connection linking strands 3 and 4. This creates a characteristic nucleotide binding site across the topological switch point between strands 1 and 4. A Gly-motif at the N-terminal region delineates the binding site of the adenosine half of the dinucleotide co-factor.