Ydgg (renamed Sqsa) controls biofilm formation in Escherichia coli K12 by altering secretion of the quorum-sensing signal autoinducer-2

The putative transport protein YdgG (344 aa) was induced 5-fold in Escherichia coli JM109 biofilms (Appl. Microbiol. Biotechnol. 64:515, 2004) and was confirmed here to control biofilm formation in complex and minimal media since deleting ydgG increased biofilm formation by 4- and 2-fold in complex and minimal media supplemented with glucose using a 96-well microtitre assay as well as increased biomass by 600-fold in flow chambers with minimal media supplemented with glucose. YdgG was also found to negatively modulate motility since transcription of flagella genes (qseB, flhD, fliA, and fliC) and a motility gene (motA) increased by 15- to 120-fold upon deletion of ydgG. Deletion of ydgG also decreased extracellular activity of autoinducer-2 by 4- to 13-fold and increased intracellular activity when glucose was added to the media by 10- to 17-fold. Using DNA microarrays and by comparing the biofilm mutant vs. the wild-type, we found deleting ydgG caused 31% of the bacterial chromosome to be differentially induced more than 2-fold, and 7.6% of the genes were repressed by more than 2-fold. YdgG not only negatively modulates expression of flagella- and motility-related genes but also all the other known products essential for biofilm formation: 4 known operons for flagella synthesis and motility (flgABCDEFGHIJ,fliEFGHIJK,fliLMNOPQR, and motABcheAW), adhesion determinants (type 1 fimbriae and the autotransporter protein Ag43), curli production, colanic acid production, and production of β-1,6-N-acetyl-D- glucoseamine polysaccharide adhesin. In addition, acrEF was induced 24-fold and this locus encodes for a known transporter of indole which is a stationary-phase, extracellular signal; indole has also been shown to influence biofilm formation. Through the microarrays, new genes related to biofilm formation were identified including transport proteins (yihN and yihP), polysialic acid production (gutM and gutQ), phage (yjfR and alpA), methionine biosynthesis (metR), biotin and thiamine biosynthesis (bioF and thiDFH), anaerobic metabolim (focB, hyfACDR, ttdA, and fumB), and genes with unknown function (ybfG, yceO, yjhQ, and yjbE). Hence, it appears ydgG controls the secretion of the quorum sensing signal AI-2 and so has been renamed sqsA.