The Gcn5-Ada2-Ada3 histone acetyltransferase module has divergent roles in pathogenesis of Candida glabrata.

Candida glabrata is an opportunistic fungal pathogen and the second most prevalent species isolated from candidiasis patients. C. glabrata has intrinsic tolerance to antifungal drugs and oxidative stresses and the ability to adhere to mucocutaneous surfaces. However, knowledge about the regulation of its virulence traits is limited. The Spt-Ada-Gcn5 acetyltransferase (SAGA) complex modulates gene transcription by histone acetylation through the histone acetyltransferase (HAT) module comprised of Gcn5-Ada2-Ada3. Previously, we showed that the ada2 mutant was hypervirulent but displayed decreased tolerance to antifungal drugs and cell wall perturbing agents. In this study, we further characterized the functions of Ada3 and Gcn5 in C. glabrata. We found that single, double, or triple deletions of the HAT module, as expected, resulted in a decreased level of acetylation on histone H3 lysine 9 (H3K9) and defective growth. These mutants were more susceptible to antifungal drugs, oxidative stresses, and cell wall perturbing agents compared with the wild-type. In addition, HAT module mutants exhibited enhanced agar invasion and upregulation of adhesin and proteases encoding genes, whereas the biofilm formation of those mutants was impaired. Interestingly, HAT module mutants exhibited enhanced induction of catalases (CTA1) expression upon treatment with H2O2 compared with the wild-type. Lastly, although ada3 and gcn5 exhibited marginal hypervirulence, the HAT double and triple mutants were hypervirulent in a murine model of candidiasis. In conclusion, the HAT module of the SAGA complex plays unique roles in H3K9 acetylation, drug tolerance, oxidative stress response, adherence, and virulence in C. glabrata.

The present study characterizes the functions of the conserved histone acetyltransferase module in the pathogenesis of the pathogenic yeast Candida glabrata. The results indicated that this module has divergent roles in the pathogenesis of C. glabrata.

A Systematic Study of the Stability, Safety, and Efficacy of the de novo Designed Antimicrobial Peptide PepD2 and Its Modified Derivatives Against Acinetobacter baumannii.

Searching for new antimicrobials is a pressing issue to conquer the emergence of multidrug-resistant (MDR) bacteria and fungi. Antimicrobial peptides (AMPs) usually have antimicrobial mechanisms different from those of traditional antibiotics and bring new hope in the discovery of new antimicrobials. In addition to antimicrobial activity, stability and target selectivity are important concerns to decide whether an antimicrobial peptide can be applied in vivo. Here, we used a simple de novo designed peptide, pepD2, which contains only three kinds of amino acid residues (W, K, L), as an example to evaluate how the residues and modifications affect the antimicrobial activity against Acinetobacter baumannii, stability in plasma, and toxicity to human HEK293 cells. We found that pepI2 with a Leu→Ile substitution can decrease the minimum bactericidal concentrations (MBC) against A. baumannii by one half (4 µg/mL). A D-form peptide, pepdD2, in which the D-enantiomers replaced the L-enantiomers of the Lys(K) and Leu(L) residues, extended the peptide half-life in plasma by more than 12-fold. PepD3 is 3-residue shorter than pepD2. Decreasing peptide length did not affect antimicrobial activity but increased the IC50 to HEK293 cells, thus increased the selectivity index (SI) between A. baumannii and HEK293 cells from 4.7 to 8.5. The chain length increase of the N-terminal acyl group and the Lys→Arg substitution greatly enhanced the hemolytic activity, hence those modifications are not good for clinical application. Unlike colistin, the action mechanism of our peptides relies on negatively charged lipids rather than lipopolysaccharides. Therefore, not only gram-negative bacteria but also gram-positive bacteria can be killed by our peptides.

Corrigendum: A Systematic Study of the Stability, Safety, and Efficacy of the de novo Designed Antimicrobial Peptide PepD2 and Its Modified Derivatives Against Acinetobacter baumannii.

[This corrects the article DOI: 10.3389/fmicb.2021.678330.].

Repurposing the thrombopoietin receptor agonist eltrombopag as an anticryptococcal agent.

In this study, a Food and Drug Administration (FDA)-approved drug with previously unreported antifungal activity was investigated for suitability for use as an anticryptococcal agent. First, we screened a compound library of 1018 FDA-approved drugs against Cryptococcus neoformans. Of 52 drugs possessing anti-Cryptococcus activity, eltrombopag was chosen due to its novel activity. The susceptibility of Cryptococcus against eltrombopag was then studied by determining the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC), while the synergy of eltrombopag with other drugs was tested by fractional inhibitory concentration index (FICI). Eltrombopag had a limited spectrum of antifungal activity against C. neoformans/C. gattii species complex (MICs of 0.125 mg/l), Candida glabrata (MIC, 0.25 mg/l), and Trichophyton rubrum (MIC, 0.5 mg/l). Eltrombopag affected cryptococcal virulence factors, including capsule and biofilm formation, melanin production, and growth ability at 37°C. Further, RNA sequencing and deletion mutant library screening experiments revealed that genes involved in the calcineurin pathway, lipid biosynthesis, membrane component, and transporter genes were associated with eltrombopag. In addition, eltrombopag showed synergism with the calcineurin inhibitor FK506 (FICI < 0.5) against Cryptococcus species. In conclusion, eltrombopag exhibited excellent antifungal activity against Cryptococcus species potentially via a mode of action which interferes with virulence factors and the calcineurin pathway, indicating that eltrombopag might be usefully repurposed as an antifungal agent for treating cryptococcosis.