The UbiI (VisC) Aerobic Ubiquinone Synthase Is Required for Expression of Type 1 Pili, Biofilm Formation, and Pathogenesis in Uropathogenic Escherichia coli

Abstract

Uropathogenic Escherichia coli (UPEC), which causes the majority of urinary tract infections (UTI), uses pilus-mediated adherence to initiate biofilm formation in the urinary tract. Oxygen gradients within E. coli biofilms regulate expression and localization of adhesive type 1 pili. A transposon mutant screen for strains defective in biofilm formation identified the ubiI (formerly visC) aerobic ubiquinone synthase gene as critical for UPEC biofilm formation. In this study, we characterized a nonpolar ubiI deletion mutant and compared its behavior to that of wild-type bacteria grown under aerobic and anoxic conditions. Consistent with its function as an aerobic ubiquinone-8 synthase, deletion of ubiI in UPEC resulted in reduced membrane potential, diminished motility, and reduced expression of chaperone-usher pathway pili. Loss of aerobic respiration was previously shown to negatively impact expression of type 1 pili. To determine whether this reduction in type 1 pili was due to an energy deficit, wildtype UPEC and the ubiI mutant were compared for energy-dependent phenotypes under anoxic conditions, in which quinone synthesis is undertaken by anaerobic quinone synthases. Under anoxic conditions, the two strains exhibited wild-type levels of motility but produced diminished numbers of type 1 pili, suggesting that the reduction of type 1 pilus expression in the absence of oxygen is not due to a cellular energy deficit. Acute-and chronic-infection studies in a mouse model of UTI revealed a significant virulence deficit in the ubiI mutant, indicating that UPEC encounters enough oxygen in the bladder to induce aerobic ubiquinone synthesis during infection. IMPORTANCEThe majority of urinary tract infections are caused by uropathogenic E. coli, a bacterium that can respire in the presence and absence of oxygen. The bladder environment is hypoxic, with oxygen concentrations ranging from 4% to 7%, compared to 21% atmospheric oxygen. This work provides evidence that aerobic ubiquinone synthesis must be engaged during bladder infection, indicating that UPEC bacteria sense and use oxygen as a terminal electron acceptor in the bladder and that this ability drives infection potential despite the fact that UPEC is a facultative anaerobe.T he distinct characteristics of biofilms make them a particularly significant concern in the clinical setting. The presence of extracellular matrix retards the penetration of antibiotics and provides protection from innate immune responses, including opsonization and phagocytosis (1, 2). In addition, the presence of environmental gradients within the biomass leads to community "division of labor," with subpopulations of bacteria exhibiting differential gene expression in response to local nutrient and oxygen availability and with some cells being essentially metabolically dormant (3-5).Recent studies in uropathogenic Escherichia coli (UPEC) biofilms have revealed the stratification of at least two types of adhesive fibers and possibly other factors in response to oxygen gradients (4)....

Biofilm formation in uropathogenic Escherichia coli: association with adhesion factor genes

“…The isolates with moderate to strong biofilm formation ability showed higher type 1 fimbria expression level compared to the bacteria with poor biofilm formation potential. This finding indicates that phenotypic expression of the type 1 fimbria is an important determinant in biofilm formation by UPEC (13,20). Soto et al (13) reported that expression of the type 1 fimbria is independently associated with biofilm formation, which was in accordance with our data.…”

Voltage-gated calcium flux mediates Escherichia coli mechanosensation

“…S20). VisC is involved in energy production for the cell and a knockout reduced membrane potential in uropathogenic E. coli (34). The visC results suggested our measurements were sensitive enough to find variants that alter calcium flux, but the 175 genes tested are unlikely to relay mechanosensation or the voltage-gated calcium current.…”

Shigella flexneri adherence factor expression in in vivo-like conditions

“…On the following day, protein A/G plus agarose beads were added to the negative IgG control samples and incubated for 1 hour at 4°C with rotation. Afterwards, the beads or resin samples were pelleted, washed six times, and boiled in acidified Laemelli lysis buffer as previously described for adherence proteins(88). After boiling, samples were neutralized with basic Laemelli lysis buffer.…”