Biology subjects

Heinzen, R. A.

Publications and source records attributed to Heinzen, R. A..

3 recordsLinked to original sources

bioRxiv2022

A toxin-antitoxin system ensures plasmid stability in Coxiella burnetii

Coxiella burnetii is the causative agent of Q fever. All C. burnetii isolates encode either an autonomous replicating plasmid (QpH1, QpDG, QpRS, or QpDV) or QpRS-like chromosomally integrated plasmid sequences. The role of the ORFs present on these sequences is unknown. Here, the role of the ORFs encoded on QpH1 was investigated. Using a new C. burnetii shuttle vector (pB-TyrB-QpH1ori) we cured Nine Mile Phase II of QpH1. The {Delta}QpH1 strain grew normally in axenic media but had a significant growth defect in Vero cells, indicating QpH1 was important for C. burnetii virulence. We developed an inducible CRISPR interference system to examine the role of individual QpH1 plasmid genes. CRISPRi of cbuA0027 resulted in significant growth defects in axenic media and THP-1 cells. The cbuA0028/cbuA0027 operon encodes CBUA0028 and CBUA0027, which are homologous to the HigB2 toxin and HigA2 anti-toxin, respectively, from Vibrio cholerae. Consistent with toxin-antitoxin systems, overexpression of cbuA0028 resulted in a severe intracellular growth defect that was rescued by co-expression of cbuA0027. CBUA0028 inhibited protein translation. CBUA0027 bound the cbuA0028 promoter (PcbuA0028) and CBUA0028, with the resulting complex binding also PcbuA0028. In summary, our data indicates C. burnetii maintains an autonomously replicating plasmid because of a plasmid-based toxin-antitoxin system.

microbiology↗

bioRxiv2022

Structural remodeling of Coxiella burnetii during its biphasic developmental cycle revealedby cryo-electron tomography

Coxiella burnetii is an obligate zoonotic bacterium that targets macrophages to cause a disease known as Q fever. It has a biphasic developmental lifecycle where the extracellular and metabolically inactive small cell variant (SCV) transforms, under host acidic environment, into the vegetative large cell variant (LCV). However, the details about the morphological and structural changes that accompany this biphasic cycle are still lacking. Here, we used cryo-electron tomography to image the different cell variants of C. burnetii grown either under axenic conditions in different pH or purified directly from host cells revealing the major developmental, morphological and structural transitions. We show that SCVs are characterized by equidistant stacks of inner membrane that presumably allow a smooth transition to LCV, a transition coupled with the expression of the Dot/Icm type IVB secretion system (T4BSS). A class of T4BSS particles were associated with extracellular densities including a tubular structure possibly involved in host interaction or effector delivery. Also, SCVs and cells in the transition state contained spherical multilayered membrane structures of different sizes and locations suggesting that they are not related to a sporulation process as once assumed.

microbiology↗

bioRxiv2022

A comprehensive phenotypic screening strategy to identify modulators of cargo translocation by the bacterial Type IVB secretion system

Bacterial type IV secretion systems (T4SSs) are macromolecular machines that translocate effector proteins across multiple membranes into infected host cells. Loss of function mutations in genes encoding protein components of the T4SS render bacteria avirulent, highlighting the attractiveness of T4SSs as drug targets. Here, we designed an automated high-throughput screening approach for the identification of compounds that interfere with the delivery of a reporter-effector fusion protein from Legionella pneumophila into RAW264.7 mouse macrophages. Using a fluorescence resonance energy transfer (FRET)-based detection assay in a bacteria/macrophage co-culture format, we screened a library of over 18,000 compounds and, upon vetting compound candidates in a variety of in vitro and cell-based secondary screens, isolated several hits that efficiently interfered with biological processes that depend on a functional T4SS, such as intracellular bacterial proliferation or lysosomal avoidance, but had no detectable effect on L. pneumophila growth in culture medium, conditions under which the T4SS is dispensable. Notably, the same hit compounds also attenuated, to varying degrees, effector delivery by the closely related T4SS from Coxiella burnetii, notably without impacting growth of this organism within synthetic media. Together, these results support the idea that interference with T4SS function is a possible therapeutic intervention strategy, and the emerging compounds provide tools to interrogate at a molecular level the regulation and dynamics of these virulence-critical translocation machines. ImportanceMulti-drug-resistant pathogens are an emerging threat to human health. Since conventional antibiotics target not only the pathogen but also eradicate the beneficial microbiota, they often cause additional clinical complications. Thus, there is an urgent need for the development of "smarter" therapeutics that selectively target pathogens without affecting beneficial commensals. The bacterial type IV secretion system (T4SS) is essential for the virulence of a variety of pathogens but dispensable for bacterial viability in general and can, thus, be considered a pathogens Achilles heel. By identifying small molecules that interfere with cargo delivery by the T4SS from two important human pathogens, Legionella pneumophila and Coxiella burnetii, our study represents the first step in our pursuit towards precision medicine by developing pathogen-selective therapeutics capable of treating the infections without causing harm to commensal bacteria.

microbiology↗