Diversity in Genetic Regulation of Bacterial Fimbriae Assembled by the Chaperone Usher Pathway.

Bacteria express different types of hair-like proteinaceous appendages on their cell surface known as pili or fimbriae. These filamentous structures are primarily involved in the adherence of bacteria to both abiotic and biotic surfaces for biofilm formation and/or virulence of non-pathogenic and pathogenic bacteria. In pathogenic bacteria, especially Gram-negative bacteria, fimbriae play a key role in bacteria-host interactions which are critical for bacterial invasion and infection. Fimbriae assembled by the Chaperone Usher pathway (CUP) are widespread within the Enterobacteriaceae, and their expression is tightly regulated by specific environmental stimuli. Genes essential for expression of CUP fimbriae are organised in small blocks/clusters, which are often located in proximity to other virulence genes on a pathogenicity island. Since these surface appendages play a crucial role in bacterial virulence, they have potential to be harnessed in vaccine development. This review covers the regulation of expression of CUP-assembled fimbriae in Gram-negative bacteria and uses selected examples to demonstrate both dedicated and global regulatory mechanisms.

Bioengineering of non-pathogenic Escherichia coli to enrich for accumulation of environmental copper.

Heavy metal sequestration from industrial wastes and agricultural soils is a long-standing challenge. This is more critical for copper since copper pollution is hazardous both for the environment and for human health. In this study, we applied an integrated approach of Darwin's theory of natural selection with bacterial genetic engineering to generate a biological system with an application for the accumulation of Cu2+ ions. A library of recombinant non-pathogenic Escherichia coli strains was engineered to express seven potential Cu2+ binding peptides encoded by a 'synthetic degenerate' DNA motif and fused to Maltose Binding Protein (MBP). Most of these peptide-MBP chimeras conferred tolerance to high concentrations of copper sulphate, and in certain cases in the order of 160-fold higher than the recognised EC50 toxic levels of copper in soils. UV-Vis spectroscopic analysis indicated a molar ratio of peptide-copper complexes, while a combination of bioinformatics-based structure modelling, Cu2+ ion docking, and MD simulations of peptide-MBP chimeras corroborated the extent of Cu2+ binding among the peptides. Further, in silico analysis predicted the peptides possessed binding affinity toward a broad range of divalent metal ions. Thus, we report on an efficient, cost-effective, and environment-friendly prototype biological system that is potentially capable of copper bioaccumulation, and which could easily be adapted for the removal of other hazardous heavy metals or the bio-mining of rare metals.

Accumulation of virulence-associated proteins in Campylobacter jejuni Outer Membrane Vesicles at human body temperature.

Campylobacter jejuni is the major cause of bacterial gastroenteritis in humans. In contrast, colonization in avian hosts is asymptomatic. Body temperature differs between human (37 °C) and avian (42 °C) hosts, and bacterial growth in 37 °C is therefore a potential cue for higher virulence properties during human infection. The proteome of the bacteria was previously shown to be altered by temperature. Here we investigated whether temperature has an effect on the C. jejuni outer membrane vesicle (OMV) proteome, as OMVs are considered to be bacterial vehicles for protein delivery and might play a role during infection. OMVs isolated from C. jejuni strain 81-176 grown at 37 °C and 42 °C were analyzed by LC-ESI-MS/MS. 181 proteins were detected in both sample groups, one protein was exclusively present, and three were absent in OMVs from 37 °C. Of the 181 proteins, 59 were differentially expressed; 30 proteins were detected with higher abundance, and 29 proteins with lower abundance at 37 °C. Among the more highly abundant proteins, significantly more proteins were predicted to be associated with virulence. These data show that temperature has an impact on the property of the OMVs, and this might affect the outcome of colonization/infection by C. jejuni in different hosts. SIGNIFICANCE: While C. jejuni is considered as a commensal bacterium in avian hosts, it causes symptomatic infection in humans. As the host body temperature is one differentiating factor, the growth temperature can potentially affect the virulence properties of the bacteria, but also OMVs that are released during growth. By using a proteomic approach, in this study, we observed that the protein content of OMVs isolated from C. jejuni is affected by growth temperature and that more proteins related to virulence are associated with OMVs at 37°C growth temperature. This property indicates that C. jejuni OMVs have a potential role for the outcome of human infection.

Campylobacter jejuni bile exposure influences outer membrane vesicles protein content and bacterial interaction with epithelial cells.

Campylobacter jejuni is a prevalent human pathogen and a major cause of bacterial gastroenteritis in the world. In humans, C. jejuni colonizes the intestinal tract and its tolerance to bile is crucial for bacteria to survive and establish infection. C. jejuni produces outer membrane vesicles (OMVs) which have been suggested to be involved in virulence. In this study, the proteome composition of C. jejuni OMVs in response to low concentration of bile was investigated. We showed that exposure of C. jejuni to low concentrations of bile, similar to the concentration in cecum, induced significant changes in the protein profile of OMVs released during growth without affecting the protein profile of the bacteria. This suggests that bile influences a selective packing of the OMVs after bacterial exposure to low bile. A low concentration of bile was found to increase bacterial adhesion to intestinal epithelial cells, likely by an enhanced hydrophobicity of the cell membrane following exposure to bile. The increased bacterial adhesiveness was not associated with increased invasion, instead bile exposure decreased C. jejuni invasion. OMVs released from bacteria upon exposure to low bile showed to increase both adhesion and invasion of non-bile-exposed bacteria into intestinal epithelial cells. These findings suggest that C. jejuni in environments with low concentrations of bile produce OMVs that facilitates colonization of the bacteria, and this could potentially contribute to virulence of C. jejuni in the gut.

Yersinia pseudotuberculosis Blocks Neutrophil Degranulation.

Neutrophils are essential components of immunity and are rapidly recruited to infected or injured tissue. Upon their activation, neutrophils release granules to the cell's exterior, through a process called degranulation. These granules contain proteins with antimicrobial properties that help combat infection. The enteropathogenic bacterium Yersinia pseudotuberculosis successfully persists as an extracellular bacterium during infection by virtue of its translocation of virulence effectors (Yersinia outer proteins [Yops]) that act in the cytosol of host immune cells to subvert phagocytosis and proinflammatory responses. Here, we investigated the effect of Y. pseudotuberculosis on neutrophil degranulation upon cell contact. We found that virulent Y. pseudotuberculosis was able to prevent secondary granule release. The blocking effect was general, as the release of primary and tertiary granules was also reduced. Degranulation of secondary granules was also blocked in primed neutrophils, suggesting that this mechanism could be an important element of immune evasion. Further, wild-type bacteria conferred a transient block on neutrophils that prevented their degranulation upon contact with plasmid-cured, avirulent Y. pseudotuberculosis and Escherichia coli Detailed analyses showed that the block was strictly dependent on the cooperative actions of the two antiphagocytic effectors, YopE and YopH, suggesting that the neutrophil target structures constituting signaling molecules needed to initiate both phagocytosis and general degranulation. Thus, via these virulence effectors, Yersinia can impair several mechanisms of the neutrophil's antimicrobial arsenal, which underscores the power of its virulence effector machinery.