Role of yqiC in the Pathogenicity of Salmonella and Innate Immune Responses of Human Intestinal Epithelium

Abstract

The yqiC gene of Salmonella enterica serovar Typhimurium (S. Typhimurium) regulates bacterial growth at different temperatures and mice survival after infection. However, the role of yqiC in bacterial colonization and host immunity remains unknown. We infected human LS174T, Caco-2, HeLa, and THP-1 cells with S. Typhimurium wild-type SL1344, its yqiC mutant, and its complemented strain. Bacterial colonization and internalization in the four cell lines significantly reduced on yqiC depletion. Post-infection production of interleukin-8 and human β-defensin-3 in LS174T cells significantly reduced because of yqiC deleted in S. Typhimurium. The phenotype of yqiC mutant exhibited few and short flagella, fimbriae on the cell surface, enhanced biofilm formation, upregulated type-1 fimbriae expression, and reduced bacterial motility. Type-1 fimbriae, flagella, SPI-1, and SPI-2 gene expression was quantified using real-time PCR. The data show that deletion of yqiC upregulated fimA and fimZ expression and downregulated flhD, fliZ, invA, and sseB expression. Furthermore, thin-layer chromatography and high-performance liquid chromatography revealed the absence of menaquinone in the yqiC mutant, thus validating the importance of yqiC in the bacterial electron transport chain. Therefore, YqiC can negatively regulate FimZ for type-1 fimbriae expression and manipulate the functions of its downstream virulence factors including flagella, SPI-1, and SPI-2 effectors.

The UbiK protein is an accessory factor necessary for bacterial ubiquinone (UQ) biosynthesis and forms a complex with the UQ biogenesis factor UbiJ

“…Our results and interpretation differ from a recent study that concluded that UbiK was involved in MK biosynthesis in Salmonella (10). This conclusion was based on an analysis of the quinone content of an ubiK mutant.…”

“…In the present study, we discovered a novel gene, namely yqiC, important for UQ biosynthesis under aerobiosis in E. coli and S. enterica. Contrary to a recent report (10), MK biosynthesis was not impaired in the yqiC mutant. We therefore propose to change the name of yqiC to ubiK.…”

“…Salmonella endogenous MK 8 in the HPLC chromatograms by Wang et al (10). Indeed, these authors used commercial vitamin K2 (MK 4 ) as a standard to identify the retention time of MK 8 in chromatograms of Salmonella lipid extracts, whereas MK 4 and MK 8 have an entirely different retention time on C18 columns.…”

A genome-wide screen in Escherichia coli reveals that ubiquinone is a key antioxidant for metabolism of long-chain fatty acids

“…UbiK is a small protein (Ͻ100 amino acids) that belongs to the BMFP (Brucella membrane fusogenic protein) superfamily. In S. typhimurium, it is involved in the regulation of flagella and fimbriae expression, motility, colonization, and virulence of the organism (29,58,59). E. coli UbiK physically interacts with a non-enzymatic ubiquinone biosynthesis player, UbiJ, and is proposed to be an assembly factor for additional Ubi proteins (29).…”

speG Is Required for Intracellular Replication of Salmonella in Various Human Cells and Affects Its Polyamine Metabolism and Global Transcriptomes

“…Our preliminary study conducted using a library of 1,440 transposon mutants of S . Typhimurium to invade HeLa cell monolayers for 10 h and a high-throughput genome-wide analysis through transposon-directed insertion-site sequencing (Chaudhuri et al, 2013 ) identified speG as a gene essential for the intracellular replication of Salmonella in human epithelial cells (Fang, 2011 ). However, it remains unknown whether this result is applicable to other cells.…”