Aerobic life requires organisms to resist the damaging effects of ROS (reactive oxygen species), particularly during stress. Extensive research has established a detailed picture of how cells respond ...to oxidative stress. Attention is now focusing on identifying the key molecular targets of ROS, which cause killing when resistance is overwhelmed. Experimental criteria used to establish such targets have differing merits. Depending on the nature of the stress, ROS cause loss of essential cellular functions or gain of toxic functions. Essential targets on which life pivots during ROS stress include membrane lipid integrity and activity of ROS-susceptible proteins, including proteins required for faithful translation of mRNA. Protein oxidation also triggers accumulation of toxic protein aggregates or induction of apoptotic cell death. This burgeoning understanding of the principal ROS targets will offer new possibilities for therapy of ROS related diseases.
Single cells in genetically homogeneous microbial cultures exhibit marked phenotypic individuality, a biological phenomenon that is considered to bolster the fitness of populations. Major phenotypes ...that are characterized by heterogeneity span the breadth of microbiology, in fields ranging from pathogenicity to ecology. The cell cycle, cell ageing and epigenetic regulation are proven drivers of heterogeneity in several of the best-known phenotypic examples. However, the full contribution of factors such as stochastic gene expression is yet to be realized.
The fungal threat to global food security Avery, Simon V.; Singleton, Ian; Magan, Naresh ...
Fungal biology,
August 2019, 2019-08-00, Letnik:
123, Številka:
8
Journal Article
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Fungi threaten the security of food supply to human populations on several fronts. They destroy up to 30 % of crop products through disease and spoilage processes, while mycotoxin-producing fungi and ...opportunistic pathogens endanger food safety. Control of these fungi is vital for improving food security, but current measures are inadequate and further challenges due to human-population growth and climate change are escalating. Investment and innovation in research on strategies to control fungal growth, harnessed through international, inter-disciplinary collaboration across socio-economic boundaries, provides one key to rising to this challenge.
Global food security remains one of the most important challenges that needs to be addressed to ensure the increasing demand for food of the fast growing human population is satisfied. Fruits and ...vegetables comprise an essential component of a healthy balanced diet as they are the major source of both macro- and micronutrients. They are particularly important for communities in developing countries whose nutrition often relies solely on a plant-based diet. Recent advances in agriculture and food processing technologies have facilitated production of fresh, nutritious and safe food for consumers. However, despite the development of sophisticated chemical and physical methods of food and equipment disinfection, fresh-cut produce and fruit juice industry still faces significant economic losses due to microbial spoilage. Furthermore, fresh produce remains an important source of pathogens that have been causing outbreaks of human illness worldwide. This chapter characterizes common spoilage and human pathogenic microorganisms associated with fresh-cut produce and fruit juice products, and discusses the methods and technology that have been developed and utilized over the years to combat them. Substantial attention is given to highlight advantages and disadvantages of using these methods to reduce microbial spoilage and their efficacy to eliminate human pathogenic microbes associated with consumption of fresh-cut produce and fruit juice products.
The growing prevalence of antifungal drug resistance coupled with the slow development of new, acceptable drugs and fungicides has raised interest in natural products (NPs) for their therapeutic ...potential and level of acceptability. However, a number of well-studied NPs are considered promiscuous molecules. In this study, the advantages of drug-drug synergy were exploited for the discovery of pairwise NP combinations with potentiated antifungal activity and, potentially, increased target specificity. A rational approach informed by previously known mechanisms of action of selected NPs did not yield novel antifungal synergies. In contrast, a high-throughput screening approach with yeast revealed 34 potential synergies from 800 combinations of a diverse NP library with four selected NPs of interest (eugenol, EUG; β-escin, ESC; curcumin, CUR; berberine hydrochloride, BER). Dedicated assays validated the most promising synergies, namely, EUG + BER, CUR + sclareol, and BER + pterostilbene (PTE) fractional inhibitory concentrations (FIC) indices ≤ 0.5 in all cases, reduced to as low as 35 (BER) and 7.9 mg L
(PTE). These three combinations synergistically inhibited a range of fungi, including human or crop pathogens
,
,
, and
, with synergy also against azole-resistant isolates and biofilms. Further investigation indicated roles for mitochondrial membrane depolarization and reactive oxygen species (ROS) formation in the synergistic mechanism of EUG + BER action. This study establishes proof-of-principle for utilizing high-throughput screening of pairwise NP interactions as a tool to find novel antifungal synergies. Such NP synergies, with the potential also for improved specificity, may help in the management of fungal pathogens.
Fungi cause diverse, serious socio-economic problems, including biodeterioration of valuable products and materials that spawns a biocides industry worth ~$11 billion globally. To help combat ...environmental fungi that commonly colonise material products, this study tested the hypothesis that combination of an approved fungicide with diverse agents approved by the FDA (Food and Drug Administration) could reveal potent combinatorial activities with promise for fungicidal applications. The strategy to use approved compounds lowers potential development risks for any effective combinations. A high-throughput assay of 1280 FDA-approved compounds was conducted to find those that potentiate the effect of iodopropynyl-butyl-carbamate (IPBC) on the growth of
Trichoderma virens
; IPBC is one of the two most widely used Biocidal Products Regulations–approved fungicides. From this library, 34 compounds in combination with IPBC strongly inhibited fungal growth. Low-cost compounds that gave the most effective growth inhibition were tested against other environmental fungi that are standard biomarkers for resistance of synthetic materials to fungal colonisation. Trifluoperazine (TFZ) in combination with IPBC enhanced growth inhibition of three of the five test fungi. The antifungal hexetidine (HEX) potentiated IPBC action against two of the test organisms. Testable hypotheses on the mechanisms of these combinatorial actions are discussed. Neither IPBC + TFZ nor IPBC + HEX exhibited a combinatorial effect against mammalian cells. These combinations retained strong fungal growth inhibition properties after incorporation to a polymer matrix (alginate) with potential for fungicide delivery. The study reveals the potential of such approved compounds for novel combinatorial applications in the control of fungal environmental opportunists.
Key points
• Search with an approved fungicide to find new fungicidal synergies in drug libraries.
• New combinations inhibit growth of key environmental fungi on different matrices.
• The approach enables a more rapid response to demand for new biocides.
The essential micronutrient copper is tightly regulated in organisms, as environmental exposure or homeostasis defects can cause toxicity and neurodegenerative disease. The principal target(s) of ...copper toxicity have not been pinpointed, but one key effect is impaired supply of iron-sulfur (FeS) clusters to the essential protein Rli1 (ABCE1). Here, to find upstream FeS biosynthesis/delivery protein(s) responsible for this, we compared copper sensitivity of yeast-overexpressing candidate targets. Overexpression of the mitochondrial ferredoxin Yah1 produced copper hyper-resistance. 55Fe turnover assays revealed that FeS integrity of Yah1 was particularly vulnerable to copper among the test proteins. Furthermore, destabilization of the FeS domain of Yah1 produced copper hypersensitivity, and YAH1 overexpression rescued Rli1 dysfunction. This copper-resistance function was conserved in the human ferredoxin, Fdx2. The data indicate that the essential mitochondrial ferredoxin is an important copper target, determining a tipping point where plentiful copper supply becomes excessive. This knowledge could help in tackling copper-related diseases.
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•Expression level of the essential mitochondrial ferredoxin determines Cu resistance•Copper targets the FeS domain of yeast Yah1•Copper action at Yah1 affects downstream, essential FeS-protein function•The function in copper resistance is conserved in the human ferredoxin, Fdx2
Vallières et al. identify the conserved ferredoxin Yah1 (Fdx2 in humans) as an important target of copper excess in cells. Copper targets the FeS domain of the ferredoxin, needed for the essential process of FeS-cluster biogenesis. This knowledge could help in tackling copper-related diseases.
Fungi that spoil foods or infect crops can have major socioeconomic impacts, posing threats to food security. The strategies needed to manage these fungi are evolving, given the growing incidence of ...fungicide resistance, tightening regulations of chemicals use and market trends imposing new food-preservation challenges. For example, alternative methods for crop protection such as RNA-based fungicides, biocontrol, or stimulation of natural plant defences may lessen concerns like environmental toxicity of chemical fungicides. There is renewed focus on natural product preservatives and fungicides, which can bypass regulations for ‘clean label’ food products. These require investment to find effective, safe activities within complex mixtures such as plant extracts. Alternatively, physical measures may be one key for fungal control, such as polymer materials which passively resist attachment and colonization by fungi. Reducing or replacing traditional chlorine treatments (e.g. of post-harvest produce) is desirable to limit formation of disinfection by-products. In addition, the current growth in lower sugar food products can alter metabolic routing of carbon utilization in spoilage yeasts, with implications for efficacy of food preservatives acting via metabolism. The use of preservative or fungicide combinations, while involving more than one chemical, can reduce total chemicals usage where these act synergistically. Such approaches might also help target different subpopulations within heteroresistant fungal populations. These approaches are discussed in the context of current challenges for food preservation, focussing on pre-harvest fungal control, fresh produce and stored food preservation. Several strategies show growing potential for mitigating or reversing the risks posed by fungi in the food supply chain.
A range of fungicides or antifungals are currently deployed to control fungi in agriculture or medicine, but resistance to current agents is growing so new approaches and molecular targets are ...urgently needed. Recently, different aminoglycoside antibiotics combined with particular transport inhibitors were found to produce strong, synergistic growth-inhibition of fungi, by synergistically increasing the error rate of mRNA translation. Here, focusing on translation fidelity as a novel target for combinatorial antifungal treatment, we tested the hypothesis that alternative combinations of agents known to affect the availability of functional amino acids would synergistically inhibit growth of major fungal pathogens. We screened 172 novel combinations against three phytopathogens (
,
, and
) and three human pathogens (
,
, and
), showing that 48 combinations inhibited strongly the growth of the pathogens; the growth inhibition effect was significantly greater with the agents combined than by a simple product of their individual effects at the same doses. Of these, 23 combinations were effective against more than one pathogen, including combinations comprising food-and-drug approved compounds, e.g., quinine with bicarbonate, and quinine with hygromycin. These combinations fractional inhibitory combination (FIC) index ≤0.5 gave up to 100% reduction of fungal growth yield at concentrations of agents which, individually, had negligible effect. No synergy was evident against bacterial, plant or mammalian cells, indicating specificity for fungi. Mode-of-action analyses for quinine + hygromycin indicated that synergistic mistranslation was the antifungal mechanism. That mechanism was not universal as bicarbonate exacerbated quinine action by increasing drug uptake. The study unveils chemical combinations and a target process with potential for control of diverse fungal pathogens, and suggests repurposing possibilities for several current therapeutics.
Populations of microbial cells may resist environmental stress by maintaining a high population-median resistance (IC
) or, potentially, a high variability in resistance between individual cells ...(heteroresistance); where heteroresistance would allow certain cells to resist high stress, provided the population was sufficiently large to include resistant cells. This study sets out to test the hypothesis that both IC
and heteroresistance may contribute to conventional minimal inhibitory concentration (MIC) determinations, using the example of spoilage-yeast resistance to the preservative sorbic acid. Across a panel of 26 diverse yeast species, both heteroresistance and particularly IC
were positively correlated with predicted MIC. A focused panel of 29 different isolates of a particular spoilage yeast was also examined (isolates previously recorded as Zygosaccharomyces bailii, but genome resequencing revealing that several were in fact hybrid species,
and
). Applying a novel high-throughput assay for heteroresistance, it was found that IC
but not heteroresistance was positively correlated with predicted MIC when considered across all isolates of this panel, but the heteroresistance-MIC interaction differed for the individual Zygosaccharomyces subspecies.
exhibited higher heteroresistance than
whereas the reverse was true for IC
, suggesting possible alternative strategies for achieving high MIC between subspecies. This work highlights the limitations of conventional MIC measurements due to the effect of heteroresistance in certain organisms, as the measured resistance can vary markedly with population (inoculum) size.
Food spoilage by fungi is a leading cause of food waste, with specialized food spoilage yeasts capable of growth at preservative concentrations above the legal limit, in part due to heteroresistance allowing small subpopulations of cells to exhibit extreme preservative resistance. Whereas heteroresistance has been characterized in numerous ecological contexts, measuring this phenotype systematically and assessing its importance are not encompassed by conventional assay methods. The development here of a high-throughput method for measuring heteroresistance, amenable to automation, addresses this issue and has enabled characterization of the contribution that heteroresistance may make to conventional MIC measurements. We used the example of sorbic acid heteroresistance in spoilage yeasts like Zygosaccharomyces spp., but the approach is relevant to other fungi and other inhibitors, including antifungals. The work shows how median resistance, heteroresistance, and inoculum size should all be considered when selecting appropriate inhibitor doses in real-world antimicrobial applications such as food preservation.
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