Advance online publication:

This section includes articles accepted for publication in Microbial Cell, which have not been released in a regular issue, yet. Please note that the PDF versions of advance publication articles are generally paginated starting with page 1. This does not correspond to the final pagination upon release of the issue it will appear in.

 

More than flipping the lid: Cdc50 contributes to echinocandin resistance by regulating calcium homeostasis in Cryptococcus neoformans

Chengjun Cao and Chaoyang Xue

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Echinocandins are the newest fungicidal drug class approved for clinical use against common invasive mycoses. Yet, they are ineffective against cryptococcosis, predominantly caused by Cryptococcus neoformans. The underlying mechanisms of innate echinocandin resistance in C. neoformans remain unclear. We know that Cdc50, the β-subunit of the lipid translocase (flippase), mediates echinocandin resistance, as loss of the CDC50 gene sensitizes C. neoformans to caspofungin, a member of the echinocandins class. We sought to elucidate how Cdc50 facilitates caspofungin resistance by performing a forward genetic screen for cdc50Δ suppressor mutations that are caspofungin resistant. We identified a novel mechanosensitive calcium channel protein Crm1 that correlates with Cdc50 function (Cao et al., 2019). In addition to regulating phospholipid translocation, Cdc50 also interacts with Crm1 to regulate intracellular calcium homeostasis and calcium/calcineurin signaling that likely drives caspofungin resistance in C. neoformans. Our study revealed a novel dual function of Cdc50 that connects lipid flippase with calcium signaling. These unexpected findings provide new insights into the mechanisms of echinocandin resistance in C. neoformans that may drive future drug design.

PDF | Published online: 20/02/2020 | In press

Raman-based sorting of microbial cells to link functions to their genes

Kang Soo Lee, Michael Wagner and Roman Stocker

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In our recent work, we developed an optofluidic platform that allows a direct link to be made between the phenotypes (functions) and the genotypes (genes) of microbial cells within natural communities. By combining stable isotope probing, optical tweezers, Raman microspectroscopy, and microfluidics, the platform performs automated Raman-based sorting of taxa from within a complex community in terms of their functional properties. In comparison with manual sorting approaches, our method provides high throughput (up to 500 cells per hour) and very high sorting accuracy (98.3 ± 1.7%), and significantly reduces the human labour required. The system provides an efficient manner to untangle the contributions of individual members within environmental and host-associated microbiomes. In this News and Thoughts, we provide an overview of our platform, describe potential applications, suggest ways in which the system could be improved, and discuss future directions in which Raman-based analysis of microbial populations might be developed.

PDF | Published online: 10/02/2020 | In press

Stable and destabilized GFP reporters to monitor calcineurin activity in Saccharomyces cerevisiae

Jutta Diessl, Arpita Nandy, Christina Schug, Lukas Habernig and Sabrina Büttner

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The protein phosphatase calcineurin is activated in response to rising intracellular Ca2+ levels and impacts fundamental cellular processes in organisms ranging from yeast to humans. In fungi, calcineurin orchestrates cellular adaptation to diverse environmental challenges and is essential for virulence of pathogenic species. To enable rapid and large-scale assessment of calcineurin activity in living, unperturbed yeast cells, we have generated stable and destabilized GFP transcriptional reporters under the control of a calcineurin-dependent response element (CDRE). Using the reporters, we show that the rapid dynamics of calcineurin activation and deactivation can be followed by flow cytometry and fluorescence microscopy. This system is compatible with live/dead staining that excludes confounding dead cells from the analysis. The reporters provide technology to monitor calcineurin dynamics during stress and ageing and may serve as a drug-screening platform to identify novel antifungal compounds that selectively target calcineurin.

PDF | Published online: 05/02/2020 | In press

Microfluidic techniques for separation of bacterial cells via taxis

Jyoti P. Gurung, Murat Gel and Matthew A. B. Baker

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The microbial environment is typically within a fluid and the key processes happen at the microscopic scale where viscosity dominates over inertial forces. Microfluidic tools are thus well suited to study microbial motility because they offer precise control of spatial structures and are ideal for the generation of laminar fluid flows with low Reynolds numbers at microbial lengthscales. These tools have been used in combination with microscopy platforms to visualise and study various microbial taxes. These include establishing concentration and temperature gradients to influence motility via chemotaxis and thermotaxis, or controlling the surrounding microenvironment to influence rheotaxis, magnetotaxis, and phototaxis. Improvements in microfluidic technology have allowed fine separation of cells based on subtle differences in motility traits and have applications in synthetic biology, directed evolution, and applied medical microbiology.

PDF | Published online: 15/01/2020 | In press

The euchromatic histone mark H3K36me3 preserves heterochromatin through sequestration of an acetyltransferase complex in fission yeast

Paula R. Georgescu, Matías Capella, Sabine Fischer-Burkart and Sigurd Braun

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Maintaining the identity of chromatin states requires mechanisms that ensure their structural integrity through the concerted actions of histone modifiers, readers, and erasers. Histone H3K9me and H3K27me are hallmarks of repressed heterochromatin, whereas H3K4me and H3K36me are associated with actively transcribed euchromatin. Paradoxically, several studies have reported that loss of Set2, the methyltransferase responsible for H3K36me, causes de-repression of heterochromatin. Here we show that unconstrained activity of the acetyltransferase complex Mst2C, which antagonizes heterochromatin, is the main cause of the silencing defects observed in Set2-deficient cells. As previously shown, Mst2C is sequestered to actively transcribed chromatin via binding to H3K36me3 that is recognized by the PWWP domain protein Pdp3. We demonstrate that combining deletions of set2+ and pdp3+ results in an epistatic silencing phenotype. In contrast, deleting mst2+, or other members of Mst2C, fully restores silencing in Set2-deficient cells. Suppression of the silencing defect in set2∆ cells is specific for pericentromeres and subtelomeres, which are marked by H3K9me, but is not seen for loci that lack genuine heterochromatin. Mst2 is known to acetylate histone H3K14 redundantly with the HAT Gnc5. Further, it is involved in the acetylation of the non-histone substrate and E3 ubiquitin ligase Brl1, resulting in increased H2B-K119 ubiquitylation at euchromatin. However, we reveal that none of these mechanisms are responsible for the Set2-dependent silencing pathway, implying that Mst2 targets another, unknown substrate critical for heterochromatin silencing. Our findings demonstrate that maintenance of chromatin states requires spatial constraint of opposing chromatin activities.

PDF | Published online: 03/01/2020 | In press

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