Single-Cell Detection of Erwinia amylovora Using Bio-Functionalized SIS Sensor

Herein, we developed a bio-functionalized solution-immersed silicon (SIS) sensor at the single-cell level to identify Erwinia amylovora (E. amylovora), a highly infectious bacterial pathogen responsible for fire blight, which is notorious for its rapid spread and destructive impact on apple and pear orchards. This method allows for ultra-sensitive measurements without pre-amplification or labeling compared to conventional methods. To detect a single cell of E. amylovora, we used Lipopolysaccharide Transporter E (LptE), which is involved in the assembly of lipopolysaccharide (LPS) at the surface of the outer membrane of E. amylovora, as a capture agent. We confirmed that LptE interacts with E. amylovora via LPS through in-house ELISA analysis, then used it to construct the sensor chip by immobilizing the capture molecule on the sensor surface modified with 3'-Aminopropyl triethoxysilane (APTES) and glutaraldehyde (GA). The LptE-based SIS sensor exhibited the sensitive and specific detection of the target bacterial cell in real time. The dose-response curve shows a linearity (R2 > 0.992) with wide dynamic ranges from 1 to 107 cells/mL for the target bacterial pathogen. The sensor showed the value change (dΨ) of approximately 0.008° for growing overlayer thickness induced from a single-cell E. amylovora, while no change in the control bacterial cell (Bacillus subtilis) was observed, or negligible change, if any. Furthermore, the bacterial sensor demonstrated a potential for the continuous detection of E. amylovora through simple surface regeneration, enabling its reusability. Taken together, our system has the potential to be applied in fields where early symptoms are not observed and where single-cell or ultra-sensitive detection is required, such as plant bacterial pathogen detection, foodborne pathogen monitoring and analysis, and pathogenic microbial diagnosis.

Crystal structure of Campylobacter jejuni lipoprotein Cj1090c

In Gram-negative bacteria, lipopolysaccharide (LPS) is an essential component of the asymmetric outer membrane (OM). LptE is an OM lipoprotein that forms a complex with the β-barrel OM protein, LptD. Incorporation of LPS into the OM outer leaflet is essential for bacterial viability, and mediated by the LptD/E complex. The genome of Campylobacter jejuni, a major foodborne pathogen, contains over 20 putative lipoproteins including Cj1090c. Here, we report the crystal structure of Cj1090c at 2.4 Å resolution, revealing structural evidence for LptE in C. jejuni. The analysis of this crystal structure, along with the genomic context, allows us to propose the C. jejuni LPS transport system for the first time, and permits for discussion of the features of the LptD/E complex of C. jejuni.

A Photo-Crosslinking Approach to Monitoring the Assembly of an LptD Intermediate with LptE in a Living Cell

Elucidating the dynamic behavior of proteins in living cells is extremely important for understanding the physiological roles of biological processes. The site-specific in vivo photo-crosslinking approach using a photoreactive unnatural amino acid enables the analysis of protein interactions with high spatial resolution in vivo. Recently, by improving the photo-crosslinking technique, we developed the "PiXie" method for the analysis of dynamic interactions of newly synthesized proteins. Here, we describe the detailed protocols of the "PiXie" method and its application to the analysis of the assembly processes of the lipopolysaccharide translocon components, a β-barrel outer membrane protein, LptD, and a lipoprotein, LptE.

Outer-membrane protein LptD (PA0595) plays a role in the regulation of alginate synthesis in Pseudomonas aeruginosa

PURPOSE

The presence of alginate-overproducing (Alg⁺) strains of Pseudomonas aeruginosa in cystic fibrosis patients is indicative of chronic infection. The Alg⁺ phenotype is generally due to a mutation in the mucA gene, encoding an innermembrane protein that sequesters AlgT/U, the alginate-specific sigma factor. AlgT/U release from the anti-sigma factor MucA is orchestrated via a complex cascade called regulated intramembrane proteolysis. The goal of this study is to identify new players involved in the regulation of alginate production.

METHODOLOGY

Previously, a mutant with a second-site suppressor of alginate production (sap), sap27, was isolated from the constitutively Alg⁺ PDO300 that harbours the mucA22 allele. A cosmid from a P. aeruginosa minimum tiling path library was identified via en masse complementation of sap27. The cosmid was transposon mutagenized to map the contributing gene involved in the alginate production. The identified gene was sequenced in sap27 along with algT/U, mucA, algO and mucP. The role of the novel gene was explored using precise in-frame algO and algW deletion mutants of PAO1 and PDO300.Results/Key findings. The gene responsible for restoring the mucoid phenotype was mapped to lptD encoding an outer-membrane protein. However, the sequencing of sap27 revealed a mutation in algO, but not in lptD. In addition, we demonstrate that lipopolysaccharide transport protein D (LptD)-dependent alginate production requires AlgW in PAO1 and AlgO in PDO300.

CONCLUSION

LptD plays a specific role in alginate production. Our findings suggest that there are two pathways for the production of alginate in P. aeruginosa, one involving AlgW in the wild-type, and one involving AlgO in the mucA22 mutant.