Biology subjects

Hackstadt, T.

Publications and source records attributed to Hackstadt, T..

3 recordsLinked to original sources

bioRxiv2024

Development of inducible promoter and CRISPRi plasmids functional in Rickettsia rickettsii.

Rickettsia rickettsii is an obligate intracellular, tick-borne bacterium that causes Rocky Mountain spotted fever. The demanding nature of cultivating these bacteria within host cells and the labor involved in obtaining clonal isolates has severely limited progress regarding the development of compatible genetic tools to study this pathogen. Conditional expression of genes which might be toxic or have an otherwise undesirable effect is the next logical goal to expand upon the constitutive expression plasmids generated thus far. We describe the construction of an inducible promoter system based on the tet-On system, leveraging design elements from the anhydrotetracycline inducible promoter system used for Borrelia burgdorferi and one of the few characterized rickettsial promoters for the outer membrane gene, rompB (sca5). The functionality of this promoter is demonstrated via fluorescence of induced mScarlet production and was then used to construct a generalized inducible expression vector for R. rickettsii. The development of a functional inducible promoter was then applied to the construction of a CRISPR interference plasmid as a means to reduce or essentially silence the transcription of targeted genes. We demonstrate the viability of a simplified, single vector CRISPRi system to disrupt gene expression in R. rickettsii targeting the type IV secreted effector rarP2 and autotransporter peptidase rapL as examples. IMPORTANCEThis work expands upon the genetic toolbox available for R. rickettsii. This is the first report of both an inducible promoter and CRISPRi system compatible with Rickettsia, which may provide key instruments for the development of further tools. The development of an inducible promoter system allows for the overexpression of genes which might be toxic when expressed constitutively. The CRISPRi system enables the ability to knockdown genes with specificity, and critically, genes which may be essential and could not otherwise be knocked out. These developments may provide the foundation for unlocking genetic tools for other pathogens of the order Rickettsiales, such as the Anaplasma, Orientia, and Ehrlichia for which there are currently no inducible promoters or CRISPRi platforms.

molecular biology↗

bioRxiv2022

Chlamydia trachomatis effectors target the mitochondria and alter mitochondrial protein composition

Mitochondria are critical cellular organelles that perform a wide variety of functions including energy production and immune regulation. To perform these functions, mitochondria contain approximately 1,500 proteins, the majority of which are encoded in the nuclear genome, translated in the cytoplasm, and translocated to the mitochondria using distinct mitochondria targeting sequences (MTS). Bacterial proteins can also contain MTS and localize to the mitochondria. For the obligate intracellular human pathogen, Chlamydia trachomatis, interaction with various host cell organelles promotes intracellular replication. However, the extent and mechanisms through which Chlamydia interact directly with mitochondria remain unclear. We investigated the presence of MTS in the C. trachomatis genome and discovered 30 genes with around 70% or greater probability of mitochondrial localization. Five are translocated to the mitochondria upon ectopic expression in HeLa cells. Mass spectrometry of isolated mitochondria from infected cells revealed that two of these proteins localize to the mitochondria during infection. Comparison of mitochondria from infected and uninfected cells suggests that chlamydial infection affects mitochondrial protein composition. Around 125 host proteins were significantly decreased or absent in mitochondria from infected cells. Among these are pro-apoptotic factors and those related to mitochondrial fission/fusion dynamics. Conversely, 82 host proteins were increased in or specific to mitochondria of infected cells, many of which act as anti-apoptotic factors and upregulators of cellular metabolism. These data support the notion that C. trachomatis specifically targets host mitochondria to manipulate cell fate decisions and metabolic function to support pathogen survival and replication. ImportanceObligate intracellular bacteria have evolved multiple means to promote their intracellular survival and replication within the otherwise harsh environment of the eukaryotic cell. Nutrient acquisition and avoidance of cellular defense mechanisms are critical to an intracellular lifestyle. Mitochondria are critical organelles that produce energy in the form of ATP and regulate programmed cell death responses to invasive pathogenic microbes. Cell death prior to completion of replication would be detrimental to the pathogen. C. trachomatis produces at least two and possibly more proteins that target the mitochondria. Collectively, C. trachomatis infection modulates mitochondrial protein composition favoring a profile suggestive of down-regulation of apoptosis.

microbiology↗

bioRxiv2022

Chlamydia trachomatis suppresses host cell store-operated Ca2+ entry and inhibits NFAT/calcineurin signaling

The obligate intracellular bacterium, Chlamydia trachomatis, replicates within a parasitophorous vacuole termed an inclusion. During development, host proteins critical for regulating intracellular calcium (Ca2+) homeostasis interact with the inclusion membrane. The inclusion membrane protein, MrcA, interacts with the inositol-trisphosphate receptor (IP3R), an ER cationic channel that conducts Ca2+. Stromal interaction molecule 1 (STIM1), an ER transmembrane protein important for regulating store-operated Ca2+ entry (SOCE), localizes to the inclusion membrane via an uncharacterized interaction. We therefore examined Ca2+ mobilization in C. trachomatis infected cells. Utilizing a variety of Ca2+ indicators to assess changes in cytosolic Ca2+ concentration, we demonstrate that C. trachomatis impairs host cell SOCE. Ca2+ regulates many cellular signaling pathways. We find that the SOCE-dependent NFAT/calcineurin signaling pathway is impaired in C. trachomatis L2 infected HeLa cells and likely has major implications on host cell physiology as it relates to C. trachomatis pathogenesis.

microbiology↗