Abstract
YbjN, encoding an enterobacteria-specific protein, is a multicopy suppressor of temperature sensitivity in the ts9 mutant strain of Escherichia coli. In this study, we further explored the role(s) of ybjN. First, we demonstrated that the ybjN transcript was about 10-fold lower in the ts9 strain compared to that of E. coli strain BW25113 (BW). Introduction of multiple copies of ybjN in the ts9 strain resulted in over-expression of ybjN by about 10-fold as compared to that of BW. These results suggested that temperature sensitivity of the ts9 mutant of E. coli may be related to expression levels of ybjN. Characterization of E. coli ybjN mutant revealed that ybjN mutation resulted in pleiotropic phenotypes, including increased motility, fimbriation (auto-aggregation), exopolysaccharide production, and biofilm formation. In contrast, over-expression of ybjN (in terms of multiple copies) resulted in reduced motility, fimbriation, 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 E. coli, suggesting similar evolution of the YbjN family proteins 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. Furthermore, over-expression of ybjN up-regulated toxin-antitoxin modules, the SOS response pathway, cold shock and starvation induced transporter genes. Collectively, these results suggest that YbjN may play important roles in regulating bacterial multicellular behavior, metabolism, and survival under stress conditions in E. coli. These results also suggest that ybjN over-expression-related temperature rescue of the ts9 mutant may be due to down-regulation of metabolic activity and activation of stress response genes in the ts9 mutant.
Highlights
Microorganisms survive in different environmental conditions by adaptation via diverse metabolic pathways
In a previous genetic screening, it has been reported that E. coli ybjN gene is a multi-copy suppressor of the coaA-associated temperature sensitivity in the ts9 mutant [8]
It was revealed that ybjN expression correlated with its ability to rescue the temperature sensitivity of the ts9 mutant strain
Summary
Microorganisms survive in different environmental conditions by adaptation via diverse metabolic pathways. Microbial genome projects have indicated that the function of about half of the genes of any given bacterial genome is still unknown [1,2]. These are annotated as genes of unknown function, and their products are typically referred to as ‘conserved’ or ‘hypothetical’ proteins. As one of the best-studied prokaryotic model organisms, Escherichia coli strain K12 still has around 2000 out of 4377 genes which have not been characterized [3] Characterization of these unknown proteins remains a major challenge and only around 30 new E. coli genes have been experimentally characterized each year [4]. These unknown proteins provide opportunities for us to better understanding the biology of a particular organism, and open up potentially new biomedical and commercial opportunities [5]
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