Table of contents

Volume 8, Issue 7, pp. 146 - 163, July 2021

Issue cover
Cover: The cover depicts the Gram-positive bacterium Staphylococcus aureus (S. aureus) producing a zone of hemolysis when grown on Blood Agar Petri plates (image created by Anthony D'Onofrio at and retrieved via Flickr; the image was modified by MIC). The cover is published under the Creative Commons Attribution (CC BY) license. Enlarge issue cover

Research Articles

Barcode sequencing and a high-throughput assay for chronological lifespan uncover ageing-associated genes in fission yeast

Catalina A. Romila, StJohn Townsend, Michal Malecki, Stephan Kamrad, María Rodríguez-López, Olivia Hillson, Cristina Cotobal, Markus Ralser and Jürg Bähler

page 146-160 | 10.15698/mic2021.07.754 | Full text | PDF | Abstract

Ageing-related processes are largely conserved, with simple organisms remaining the main platform to discover and dissect new ageing-associated genes. Yeasts provide potent model systems to study cellular ageing owing their amenability to systematic functional assays under controlled conditions. Even with yeast cells, however, ageing assays can be laborious and resource-intensive. Here we present improved experimental and computational methods to study chronological lifespan in Schizosaccharomyces pombe. We decoded the barcodes for 3206 mutants of the latest gene-deletion library, enabling the parallel profiling of ~700 additional mutants compared to previous screens. We then applied a refined method of barcode sequencing (Bar-seq), addressing technical and statistical issues raised by persisting DNA in dead cells and sampling bottlenecks in aged cultures, to screen for mutants showing altered lifespan during stationary phase. This screen identified 341 long-lived mutants and 1246 short-lived mutants which point to many previously unknown ageing-associated genes, including 46 conserved but entirely uncharacterized genes. The ageing-associated genes showed coherent enrichments in processes also associated with human ageing, particularly with respect to ageing in non-proliferative brain cells. We also developed an automated colony-forming unit assay to facilitate medium- to high-throughput chronological-lifespan studies by saving time and resources compared to the traditional assay. Results from the Bar-seq screen showed good agreement with this new assay. This study provides an effective methodological platform and identifies many new ageing-associated genes as a framework for analysing cellular ageing in yeast and beyond.


LasR-regulated proteases in acute vs. chronic lung infection: a double-edged sword

Lisa C. Hennemann and Dao Nguyen

page 161-163 | 10.15698/mic2021.07.755 | Full text | PDF | Abstract

Pseudomonas aeruginosa is a gram-negative opportunistic pathogen capable of causing both acute and chronic infections, particularly in individuals with compromised host defenses. The quorum sensing transcriptional activator LasR is widely recognized for its role in regulating the expression of acute virulence factors, notably several secreted proteases which cause direct host damage and subvert host immunity in acute infections. Paradoxically, lung infections caused by LasR-deficient variants, which are found in at least a third of cystic fibrosis (CF) patients with chronic P. aeruginosa infections, are associated with accelerated lung disease and increased markers of inflammation compared to infections caused by strains with a functional LasR system. While the loss of LasR function often (although not always) results in impaired production of LasR-controlled acute virulence factors, the implication of this pathoadaptation on host-pathogen interactions and chronic disease pathology is less well recognized. We recently observed that loss of LasR function in lasR variants, which results in impaired secreted protease production, led to increased expression of the membrane-bound surface adhesion molecule mICAM-1 in the airway epithelium, and increased neutrophilic inflammation. Specifically, human airway epithelial cells stimulated with lasR variants had higher mICAM-1 expression and greater neutrophil binding in vitro compared to stimulation with wild-type P. aeruginosa. In a subacute non-lethal P. aeruginosa lung infection model, lasR variant infection also induced higher mICAM-1 expression in the murine airway epithelium and was associated with increased neutrophilic pulmonary inflammation in vivo. Here, we discuss how (loss of) LasR function and LasR-regulated proteases affect host immunity, inflammation and tissue pathology in acute vs. chronic P. aeruginosa lung infection.

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