Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2011
Publication Date: 9/27/2011
Citation: Wang, D., Calla, B., Vimolmangkang, S., Korban, S.S., Wu, X., Huber, S.C., Clough, S.J., Zhao, Y. 2011. The orphan gene ybjN conveys pleiotropic effects on multicellular behavior and survival of Escherichia coli. PLoS One. 6(9):e25293. Interpretive Summary: Although many genomes have been sequenced, the function of many individual genes is still unkown. Some estimate about 50% or more of the genes of any organized are of unknown function. In this project, we determined the function of an E. coli gene whose function was previously unknown, by studying the gene initially in a bacterium that is closely related to E. coli. By studying how this gene, ybjN, functioned in the plant pathogenic bacterium Erwinia amylovora we were able to find that the gene plays an important role in both E. amylovora and E. coli in regulating their response to environmental stresses. The work will be of interest to both the medical and plant pathology fields.
Technical Abstract: YbjN, an enterobacteria-specific protein, is a multicopy suppressor of ts9 temperature sensitivity in Escherichia coli. In this study, we further explored the roles of ybjN, an orphan gene in E. coli. First, we demonstrated that ybjN gene was down-regulated about 10-fold in ts9 strain compared to that of the wild type strain (WT). Introduction of multiple copies of ybjN in ts9 strain resulted in ybjN over-expression for about 10-fold as compared to that of the WT. These results suggested that the temperature sensitivity of Es. coli ts9 mutant may be related to expression level of ybjN. We then determined that the expression of ybjN was higher at logarithmic phase and low (37°C) temperature than those at stationary phase and high (42°C) temperature in the WT strain, in part explaining why the ts9 strain complemented with ybjN gene can grow at 37°C, but not at 40°C. Characterization of Es. coli ybjN mutant revealed that ybjN mutation caused pleiotropic phenotypes, including increased motility, fimbriation, exopolysaccharide production, and biofilm formation. In contrast, over-expression of ybjN (in terms of multicopy) resulted in reduced motility, fimbriation (auto-aggregation), exopolysaccharide production, biofilm formation and acid resistance. In addition, our results indicate that a ybjN-homolog gene from Erwinia amylovora, a plant enterobacterial pathogen, is functionally conserved with that of Es. coli, suggesting similar evolution of YbjN family protein in enterobacteria. A microarray study revealed that the expression level of ybjN was inversely correlated with the expression of flagellar, fimbrial and acid resistance genes. Over-expression of ybjN significantly down-regulated genes involved in citric acid cycle, glycolysis, the glyoxylate shunt, oxidative phosphorylation, amino acid and nucleotide metabolism. On the other hand, over-expression of ybjN up-regulated toxin-antitoxin modules, the SOS responsive pathway, cold shock proteins and starvation induced transporter genes. Our results collectively suggest that YbjN may play important roles in regulating bacterial multicellular behaviors, metabolism and survival under various stress conditions in Es. coli. These results also suggest that ybjN over-expression-related temperature rescue of ts9 mutant may be due to down-regulation of metabolic activity and activation of stress responsive genes in the ts9 mutant.