Proper Sterol Distribution Is Required for Candida albicans Hyphal Formation and Virulence

Mediator Engineering of Saccharomyces cerevisiae To Improve Multidimensional Stress Tolerance

Saccharomyces cerevisiae is a well-performing workhorse in chemical production, which encounters complex environmental stresses during industrial processes. We constructed a multiple stress tolerance mutant, Med15^V76R/R84K, that was obtained by engineering the KIX domain of Mediator tail subunit Med15. Med15^V76R/R84K interacted with transcription factor Hap5 to improve ARV1 expression for sterol homeostasis for decreasing membrane fluidity and thereby enhancing acid tolerance. Med15^V76R/R84K interacted with transcription factor Mga2 to improve GIT1 expression for phospholipid biosynthesis for increasing membrane integrity and thereby improving oxidative tolerance. Med15^V76R/R84K interacted with transcription factor Aft1 to improve NFT1 expression for inorganic ion transport for reducing membrane permeability and thereby enhancing osmotic tolerance. Based on this Med15 mutation, Med15^V76R/R84K, the engineered S. cerevisiae strain, showed a 28.1% increase in pyruvate production in a 1.0-L bioreactor compared to that of S. cerevisiae with its native Med15. These results indicated that Mediator engineering provides a potential alternative for improving multidimensional stress tolerance in S. cerevisiae. IMPORTANCE This study identified the role of the KIX domain of Mediator tail subunit Med15 in response to acetic acid, H₂O₂, and NaCl in S. cerevisiae. Engineered KIX domain by protein engineering, the mutant strain Med15^V76R/R84K, increased multidimensional stress tolerance and pyruvate production compared with that of S. cerevisiae with its native Med15. The Med15^V76R/R84K could increase membrane related genes expression possibly by enhancing interaction with transcription factor to improve membrane physiological functions under stress conditions.

Effects of Complex Electromagnetic Fields on Candida albicans Adhesion and Proliferation on Polyacrylic Resin

(1) Background: The objectives of this study were to evaluate the effect of several sessions of the antibacterial protocol of complex electromagnetic fields (CMFs) on planktonic Candida albicans and fungal ability, after treatment with CMFs, to adhere and proliferate on acrylic resin materials. (2) Methods: Planktonic overnight cultures of Candida albicans were subjected to different entities of CMFs treatments. Four test groups were compared: “p1”: treated only with the first program of the antibacterial protocol; “p1–p5” subjected to the first five programs; “1 antibacterial” received one complete session of the protocol and “2 antibacterial” received two complete sessions. After the treatments, the number of colony forming units (CFUs) were recorded. Then, C. albicans broth cultures were cultivated on polyacrylic resin discs and evaluated for CFUs and subjected to scanning electron microscope (SEM) analysis. (3) Results: Microbiological analysis showed that CMFs promoted a significant reduction of C. albicans CFUs when the protocol “p1–p5” was applied. No statistically significant differences between test groups were observed if the time of exposure to CMFs was increased. SEM observations and CFUs showed that CMFs treatments have the ability to reduce C. albicans adherence and proliferation on discs. (4) Conclusions: The CMFs showed an antifungal effect as well as a decrease in C. albicans adhesion on polyacrylic resin.

Dodonaea viscosa var angustifolia derived 5,6,8-trihydroxy-7,4' dimethoxy flavone inhibits ergosterol synthesis and the production of hyphae and biofilm in Candida albicans

ETHNOPHARMACOLOGICAL RELEVANCE

Candida albicans is developing resistance to existing drugs increasing morbidity and mortality, which elevates an immediate need to explore new antifungal agents. Phytochemicals are an excellent source of therapeutic agents. We previously reported the antifungal activity of the crude extract of Dodonaea viscosa var. angustifolia Jacq. (DVA) from which a beneficial compound flavone: 5,6,8-trihydroxy-7,4' dimethoxy flavone (5,6,8-trihydroxy-7-methoxy-2-(4-methoxyphenyl)-4H-chromen-4-one) abbreviated as TMMC, was extracted.

AIM OF THE STUDY

The present study evaluated the effect of a TMMC subfraction on biofilms, membrane stability, ergosterol biosynthesis and germ tube (GT) formation in Candida albicans.

MATERIALS AND METHODS

Extracts were prepared and fractionated to obtain purified TMMC. Minimum inhibitory concentrations of TMMC were obtained and subinhibitory concentrations were selected for further studies. Confocal laser scanning microscopy (CLSM) was performed to assess the effect of TMMC on membrane permeability and sterol deposition using propidium iodide (PI) and filipin stains, respectively.

RESULTS

Minimum inhibitory concentrations (MIC) and Minimum Fungicidal concentrations (MFC) of TMMC were 0.39 mg/mL and 1.56 mg/mL, respectively. TMMC inhibited biofilm formation and damaged mature biofilms at 0.39 mg/mL and 1.56 mg/mL, respectively. CLSM further confirmed the disruption and architectural changes in biofilms following treatment with TMMC. TMMC also inhibited GT formation and ergosterol biosynthesis in a concentration dependent manner, which was further confirmed by varying sterol distribution and membrane disruption in treated and untreated cells.

CONCLUSIONS

With the multiple targets at different concentrations, TMMC warrants its potential use as antifungal drug against C. albicans. However further studies using animal models and more mechanistic approaches will be required.

ERG11 couples oxidative stress adaptation, hyphal elongation and virulence in Candida albicans

Candida albicans is a major fungal opportunistic pathogen for humans. In the treatment of C. albicans, azole drugs target the sterol 14α-demethylase (CYP51) encoded by ERG11 gene. Most studies have focused on the fact that the ERG11 mutant results in drug resistance, but its mechanism of action as a drug target has not been described yet. Our results showed that deletion of ERG11 reduced filamentous and invasive growth, and impaired hyphal elongation in sensing serum. Lack of ERG11 increased susceptibility to H2O2 and was defective in clearing reactive oxygen species. ERG11 may affect oxidative stress adaptation by specifically downregulating CAT1 expression. In addition, C. albicans cells lacking ERG11 were more efficiently killed by macrophages and became avirulent in vivo. This study is the first to indicate that ERG11 plays an essential role in hyphal elongation, oxidative stress adaptation and virulence in C. albicans. We speculated that azole drugs not only inhibit the growth of C. albicans, but also assist the host immune system in clearing the fungal organism. The new understanding of mechanisms of action of antifungal drugs should facilitate the development of treatment strategies for resistant fungal infections.

Harnessing Metal Homeostasis Offers Novel and Promising Targets Against Candida albicans

Fungal infections, particularly of Candida species, which are the commensal organisms of human, are one of the major debilitating diseases in immunocompromised patients. The limited number of antifungal drugs available to treat Candida infections, with the concomitant increasing incidence of multidrug-resistant (MDR) strains, further worsens the therapeutic options. Thus, there is an urgent need for the better understanding of MDR mechanisms, and their reversal, by employing new strategies to increase the efficacy and safety profiles of currently used therapies against the most prevalent human fungal pathogen, Candida albicans. Micronutrient availability during C. albicans infection is regarded as a critical factor that influences the progression and magnitude of the disease. Intracellular pathogens colonize a variety of anatomical locations that are likely to be scarce in micronutrients, as a defense strategy adopted by the host, known as nutritional immunity. Indispensable critical micronutrients are required both by the host and by C. albicans, especially as a cofactor in important metabolic functions. Since these micronutrients are not freely available, C. albicans need to exploit host reservoirs to adapt within the host for survival. The ability of pathogenic organisms, including C. albicans, to sense and adapt to limited micronutrients in the hostile environment is essential for survival and confers the basis of its success as a pathogen. This review describes that micronutrients availability to C. albicans is a key attribute that may be exploited when one considers designing strategies aimed at disrupting MDR in this pathogenic fungi. Here, we discuss recent advances that have been made in our understanding of fungal micronutrient acquisition and explore the probable pathways that may be utilized as targets.

The influence of N and S poles of static magnetic field (SMF) on Candida albicans hyphal formation and antifungal activity of amphotericin B

Due to the increasing number of Candida albicans’ infections and the resistance of this pathogenic fungus to drugs, new therapeutic strategies are sought. One of such strategies may be the use of static magnetic field (SMF). C. albicans cultures were subjected to static magnetic field of the induction 0.5 T in the presence of fluconazole and amphotericin B. We identified a reduction of C. albicans hyphal length. Also, a statistically significant additional effect on the viability of C. albicans was revealed when SMF was combined with the antimycotic drug amphotericin B. The synergistic effect of this antimycotic and SMF may be due to the fact that amphotericin B binds to ergosterol in plasma membrane and SMF similarly to MF could influence domain orientation in plasma membrane (PM).

Localization and functional characterization of the pathogenesis-related proteins Rbe1p and Rbt4p in Candida albicans

Members of the Cysteine-rich secretory protein, Antigen 5 and Pathogenesis-related 1 (CAP) protein superfamily are important virulence factors in fungi but remain poorly characterized on molecular level. Here, we investigate the cellular localization and molecular function of Rbe1p and Rbt4p, two CAP family members from the human pathogen Candida albicans. We unexpectedly found that Rbe1p localizes to budding sites of yeast cells in a disulfide bond-dependent manner. Furthermore, we show that Rbe1p and Rbt4p bind free cholesterol in vitro and export cholesteryl acetate in vivo. These findings suggest a previously undescribed role for Rbe1p in cell wall-associated processes and a possible connection between the virulence attributes of fungal CAP proteins and sterol binding.

Widespread Genetic Incompatibilities between First-Step Mutations during Parallel Adaptation of Saccharomyces cerevisiae to a Common Environment

Independently evolving populations may adapt to similar selection pressures via different genetic changes. The interactions between such changes, such as in a hybrid individual, can inform us about what course adaptation may follow and allow us to determine whether gene flow would be facilitated or hampered following secondary contact. We used Saccharomyces cerevisiae to measure the genetic interactions between first-step mutations that independently evolved in the same biosynthetic pathway following exposure to the fungicide nystatin. We found that genetic interactions are prevalent and predominantly negative, with the majority of mutations causing lower growth when combined in a double mutant than when alone as a single mutant (sign epistasis). The prevalence of sign epistasis is surprising given the small number of mutations tested and runs counter to expectations for mutations arising in a single biosynthetic pathway in the face of a simple selective pressure. Furthermore, in one third of pairwise interactions, the double mutant grew less well than either single mutant (reciprocal sign epistasis). The observation of reciprocal sign epistasis among these first adaptive mutations arising in the same genetic background indicates that partial postzygotic reproductive isolation could evolve rapidly between populations under similar selective pressures, even with only a single genetic change in each. The nature of the epistatic relationships was sensitive, however, to the level of drug stress in the assay conditions, as many double mutants became fitter than the single mutants at higher concentrations of nystatin. We discuss the implications of these results both for our understanding of epistatic interactions among beneficial mutations in the same biochemical pathway and for speciation.