3 research outputs found
Candida albicans-induced epithelial damage mediates translocation through intestinal barriers
ABSTRACT Life-threatening systemic infections often occur due to the translocation of pathogens across the gut barrier and into the bloodstream. While the microbial and host mechanisms permitting bacterial gut translocation are well characterized, these mechanisms are still unclear for fungal pathogens such as Candida albicans, a leading cause of nosocomial fungal bloodstream infections. In this study, we dissected the cellular mechanisms of translocation of C. albicans across intestinal epithelia in vitro and identified fungal genes associated with this process. We show that fungal translocation is a dynamic process initiated by invasion and followed by cellular damage and loss of epithelial integrity. A screen of >2,000 C. albicans deletion mutants identified genes required for cellular damage of and translocation across enterocytes. Correlation analysis suggests that hypha formation, barrier damage above a minimum threshold level, and a decreased epithelial integrity are required for efficient fungal translocation. Translocation occurs predominantly via a transcellular route, which is associated with fungus-induced necrotic epithelial damage, but not apoptotic cell death. The cytolytic peptide toxin of C. albicans, candidalysin, was found to be essential for damage of enterocytes and was a key factor in subsequent fungal translocation, suggesting that transcellular translocation of C. albicans through intestinal layers is mediated by candidalysin. However, fungal invasion and low-level translocation can also occur via non-transcellular routes in a candidalysin-independent manner. This is the first study showing translocation of a human-pathogenic fungus across the intestinal barrier being mediated by a peptide toxin. IMPORTANCE Candida albicans, usually a harmless fungus colonizing human mucosae, can cause lethal bloodstream infections when it manages to translocate across the intestinal epithelium. This can result from antibiotic treatment, immune dysfunction, or intestinal damage (e.g., during surgery). However, fungal processes may also contribute. In this study, we investigated the translocation process of C. albicans using in vitro cell culture models. Translocation occurs as a stepwise process starting with invasion, followed by epithelial damage and loss of epithelial integrity. The ability to secrete candidalysin, a peptide toxin deriving from the hyphal protein Ece1, is key: C. albicans hyphae, secreting candidalysin, take advantage of a necrotic weakened epithelium to translocate through the intestinal layer
Light-Dependent Control of Bacterial Expression at the mRNA Level
Sensory photoreceptors mediate numerous light-dependent
adaptations
across organisms. In optogenetics, photoreceptors achieve the reversible,
non-invasive, and spatiotemporally precise control by light of gene
expression and other cellular processes. The light-oxygen-voltage
receptor PAL binds to small RNA aptamers with sequence specificity
upon blue-light illumination. By embedding the responsive aptamer
in the ribosome-binding sequence of genes of interest, their expression
can be downregulated by light. We developed the pCrepusculo and pAurora
optogenetic systems that are based on PAL and allow to down- and upregulate,
respectively, bacterial gene expression using blue light. Both systems
are realized as compact, single plasmids that exhibit stringent blue-light
responses with low basal activity and up to several 10-fold dynamic
range. As PAL exerts light-dependent control at the RNA level, it
can be combined with other optogenetic circuits that control transcription
initiation. By integrating regulatory mechanisms operating at the
DNA and mRNA levels, optogenetic circuits with emergent properties
can thus be devised. As a case in point, the pEnumbra setup permits
to upregulate gene expression under moderate blue light whereas strong
blue light shuts off expression again. Beyond providing novel signal-responsive
expression systems for diverse applications in biotechnology and synthetic
biology, our work also illustrates how the light-dependent PAL-aptamer
interaction can be harnessed for the control and interrogation of
RNA-based processes