B-302. A Functional Type 3 Secretion System Is Required for Flagella Assembly in Enteropathogenic Escherichia coli

J. Xicohtencatl-Cortes1, P. Samadder1, Z. Saldana1, J. Puente2, J. Puente2, J. A. Girón1;
1Univ. of Arizona, Tucson, AZ, 2Inst. de Biotecnología, Univ. Autónoma de México, Cuernavaca, Morelos, MEXICO.

In enteropathogenic Escherichia coli (EPEC) the production of flagella and the type 3-secretion system (T3SS) is coupled in the presence of host epithelial cells but not in DMEM tissue culture medium. The goal of this study was to investigate the relationship between flagella and the T3SS and provide clues regarding the environmental signals that activate both secretion systems. We found that isogenic mutants deficient in assembling the T3SS machinery (escC, escV, espA, and espB) or secreting effector molecules (escN, sepD, and sepL) were not able to produce flagella after growth in DMEM and thus, were non-motile. The lack of flagella in the T3SS mutants was not due to down-regulation of flagellin gene (fliC) expression but to the lack of flagellin in these mutants. We found that the presence of sodium bicarbonate in DMEM was responsible for flagella down-regulation but it had no effect on T3 secretion. In the presence of epithelial cells, only the escC, escV, sepD, and sepL mutants retained the ability to synthesize flagellin, but were poor producers of flagella. While the fliC mutant showed no deficiency in secretion of T3SS effectors or formation of attaching and effacing lesions, the motB mutant appeared to hypersecrete Esps. We also found that mutations in virulence regulators perA, ler, grlA or grlR led to poor or no flagella production, whereas mutations in quorum sensing-associated qseB or qseC genes resulted in increased production of flagella. Similarities and differences exist between the signals that activate flagella or T3SS. In sum, our data indicate that a functional T3SS is required for flagella assembly and strongly suggest a complex, and yet to be determined, molecular cross talk between these two T3 secretion machineries.