The Burkholderia pseudomallei Proteins BapA and BapC Are Secreted TTSS3 Effectors and BapB Levels Modulate Expression of BopE

Analysis of the role of the QseBC two-component sensory system in epinephrine-induced motility and intracellular replication of Burkholderia pseudomallei

Burkholderia pseudomallei is a facultative intracellular bacterial pathogen that causes melioidosis, a severe invasive disease of humans. We previously reported that the stress-related catecholamine hormone epinephrine enhances motility of B. pseudomallei, transcription of flagellar genes and the production of flagellin. It has been reported that the QseBC two-component sensory system regulates motility and virulence-associated genes in other Gram-negative bacteria in response to stress-related catecholamines, albeit disparities between studies exist. We constructed and whole-genome sequenced a mutant of B. pseudomallei with a deletion spanning the predicted qseBC homologues (bpsl0806 and bpsl0807). The ΔqseBC mutant exhibited significantly reduced swimming and swarming motility and reduced transcription of fliC. It also exhibited a defect in biofilm formation and net intracellular survival in J774A.1 murine macrophage-like cells. While epinephrine enhanced bacterial motility and fliC transcription, no further reduction in these phenotypes was observed with the ΔqseBC mutant in the presence of epinephrine. Plasmid-mediated expression of qseBC suppressed bacterial growth, complicating attempts to trans-complement mutant phenotypes. Our data support a role for QseBC in motility, biofilm formation and net intracellular survival of B. pseudomallei, but indicate that it is not essential for epinephrine-induced motility per se.

Biarsenical fluorescent probes for multifunctional site-specific modification of proteins applicable in life sciences: an overview and future outlook

Fluorescent modification of proteins of interest (POI) in living cells is desired to study their behaviour and functions in their natural environment. In a perfect setting it should be easy to perform, inexpensive, efficient and site-selective. Although multiple chemical and biological methods have been developed, only a few of them are applicable for cellular studies thanks to their appropriate physical, chemical and biological characteristics. One such successful system is a tetracysteine tag/motif and its selective biarsenical binders (e.g. FlAsH and ReAsH). Since its discovery in 1998 by Tsien and co-workers, this method has been enhanced and revolutionized in terms of its efficiency, formed complex stability and breadth of application. Here, we overview the whole field of knowledge, while placing most emphasis on recent reports. We showcase the improvements of classical biarsenical probes with various optical properties as well as multifunctional molecules that add new characteristics to proteins. We also present the evolution of affinity tags and motifs of biarsenical probes demonstrating much more possibilities in cellular applications. We summarize protocols and reported observations so both beginners and advanced users of biarsenical probes can troubleshoot their experiments. We address the concerns regarding the safety of biarsenical probe application. We showcase examples in virology, studies on receptors or amyloid aggregation, where application of biarsenical probes allowed observations that previously were not possible. We provide a summary of current applications ranging from bioanalytical sciences to allosteric control of selected proteins. Finally, we present an outlook to encourage more researchers to use these magnificent probes.

One-step, multiplex, dual-function oligonucleotide of loop-mediated isothermal amplification assay for the detection of pathogenic Burkholderia pseudomallei

This study highlights the development of a multiplex real-time loop-mediated isothermal amplification assay. The developed assay employed a dual-function oligonucleotide (DFO) which simultaneously monitors the emitted amplification signals and accelerates the amplification process. The DFO was a modification of loop primer (LP); the 5'-end and 3'-end of the LP was tagged with fluorophore and quencher, respectively. The DFO was quenched in its unbound state and fluoresces only when it anneals to the specific target during the amplification process. With the same working mechanism as LP, DFO allowed the detection of target genes in less than 1 h in a real time monitoring system. We demonstrated this detection platform with Burkholderia pseudomallei, the causative agent of melioidosis. An internal amplification control (IAC) was incorporated in the assay to rule out false negative result and to demonstrate that the assay was successfully developed in a multiplex system. The assay was 100% specific when it was evaluated against 96 B. pseudomallei clinical isolates and 48 other bacteria species. The detection limit (sensitivity) of the developed assay was 1 fg/μl of B. pseudomallei genomic DNA and 18.2 CFU/ml at the bacterial cell level. In spiked blood samples, the assay's detection limit was 14 CFU/ml. The assay's diagnostic evaluation showed 100% diagnostic sensitivity, diagnostic specificity, positive predictive value, and negative predictive value. An integrated multiplex LAMP and real-time monitoring system was successfully developed, simplifying the workflow for the rapid and specific nucleic acid diagnostic test.

Type III Secretion in the Melioidosis Pathogen Burkholderia pseudomallei

Burkholderia pseudomallei is a Gram-negative intracellular pathogen and the causative agent of melioidosis, a severe disease of both humans and animals. Melioidosis is an emerging disease which is predicted to be vastly under-reported. Type III Secretion Systems (T3SSs) are critical virulence factors in Gram negative pathogens of plants and animals. The genome of B. pseudomallei encodes three T3SSs. T3SS-1 and -2, of which little is known, are homologous to Hrp2 secretion systems of the plant pathogens Ralstonia and Xanthomonas. T3SS-3 is better characterized and is homologous to the Inv/Mxi-Spa secretion systems of Salmonella spp. and Shigella flexneri, respectively. Upon entry into the host cell, B. pseudomallei requires T3SS-3 for efficient escape from the endosome. T3SS-3 is also required for full virulence in both hamster and murine models of infection. The regulatory cascade which controls T3SS-3 expression and the secretome of T3SS-3 have been described, as well as the effect of mutations of some of the structural proteins. Yet only a few effector proteins have been functionally characterized to date and very little work has been carried out to understand the hierarchy of assembly, secretion and temporal regulation of T3SS-3. This review aims to frame current knowledge of B. pseudomallei T3SSs in the context of other well characterized model T3SSs, particularly those of Salmonella and Shigella.