Mucor circinelloides and other members of Mucorales are filamentous fungi, widely used as model organisms in basic and applied studies. Although genetic manipulation methods have been described for ...some Mucoral fungi, construction of stable integrative transformants by homologous recombination has remained a great challenge in these organisms. In the present study, a plasmid free CRISPR-Cas9 system was firstly developed for the genetic modification of a Mucoral fungus. The described method offers a rapid but robust tool to obtain mitotically stable mutants of M. circinelloides via targeted integration of the desired DNA. It does not require plasmid construction and its expression in the recipient organism. Instead, it involves the direct introduction of the guide RNA and the Cas9 enzyme and, in case of homology directed repair (HDR), the template DNA into the recipient strain. Efficiency of the method for non-homologous end joining (NHEJ) and HDR was tested by disrupting two different genes, i.e. carB encoding phytoene dehydrogenase and hmgR2 encoding 3-hydroxy-3-methylglutaryl-CoA reductase, of M. circinelloides. Both NHEJ and HDR resulted in stable gene disruption mutants. While NHEJ caused extensive deletions upstream from the protospacer adjacent motif, HDR assured the integration of the deletion cassette at the targeted site.
Mucormycosis is an invasive fungal infection caused by certain members of the fungal order of Mucorales. The species most frequently identified as the etiological agents of mucormycosis belong to the ...genera
,
, and
. The frequency of systemic mucormycosis has been increasing, mainly because of increasing numbers of susceptible patients. Furthermore, Mucorales display intrinsic resistance to the majority of routinely used antifungal agents (e.g., echinocandins and short-tailed azoles), which limits the number of possible therapeutic options. All the above-mentioned issues urge the improvement of molecular identification methods and the discovery of new antifungal targets and strategies. Spore coat proteins (CotH) constitute a kinase family present in many pathogenic bacteria and fungi and participate in the spore formation in these organisms. Moreover, some of them can act as virulence factors being receptors of the human GRP78 protein during Rhizopus delemar-induced mucormycosis. We identified 17
-like genes in the Mucor lusitanicus genome database. Successful disruption of five
genes in
was performed using the CRISPR-Cas9 system. The CotH3 and CotH4 proteins play a role in adaptation to different temperatures as well as in developing the cell wall structure. We also show CotH4 protein is involved in spore wall formation by affecting the total chitin content and, thus, the composition of the spore wall. The role of CotH3 and CotH4 proteins in virulence was confirmed in two invertebrate models and a diabetic ketoacidosis (DKA) mouse model.
Current treatment options for mucormycosis are inadequate, resulting in high mortality rates, especially among immunosuppressed patients. The development of novel therapies for mucormycosis has been hampered by lack of understanding of the pathogenetic mechanisms. The importance of the cell surface CotH proteins in the pathogenesis of
-mediated mucormycosis has been recently described. However, the contribution of this family of proteins to the virulence of other mucoralean fungi and their functionality in vital processes remain undefined. Through the use of the CRISPR-Case9 gene disruption system, we demonstrate the importance of several of the CotH proteins to the virulence of Mucor lusitanicus by using three infection models. We also report on the importance of one of these proteins, CotH4, to spore wall formation by affecting chitin content. Therefore, our studies extend the importance of CotH proteins to
and identify the mechanism by which one of the CotH proteins contributes to the development of a normal fungal cell wall, thereby indicating that this family of proteins can be targeted for future development of novel therapeutic strategies of mucormycosis.
Members of the
species complex are the second most frequently isolated pathogens after
from cystic fibrosis (CF) patients with fungal pulmonary infections. Even so, the main risk factors for the ...infection are unrevealed. According to previous studies, bacterial infections might reduce the risk of a fungal infection, but an antibacterial therapy may contribute to the airway colonization by several fungal pathogens. Furthermore, corticosteroids, which are often used to reduce lung inflammation in children and adults with CF, are also proved to enhance the growth of
. Considering all the above discussed points, we aimed to test how
influences the growth of scedosporia and to investigate the potential effect of commonly applied antibacterial agents and corticosteroids on
species. Direct interactions between fungal and bacterial strains were tested using the disk inhibition method. Indirect interactions via volatile compounds were investigated by the plate-in-plate method, while the effect of bacterial media-soluble molecules was tested using a modified cellophane assay and also in liquid culture media conditioned by
. To test the effect of bacterial signal molecules, antibacterial agents and corticosteroids on the fungal growth, the broth microdilution method was used. We also investigated the germination ability of
conidia in the presence of pyocyanin and diffusible signal factor by microscopy. According to our results,
either inhibited or enhanced the growth of scedosporia depending on the culture conditions and the mode of interactions. When the two pathogens were cultured physically separately from each other in the plate-in-plate tests, the presence of the bacteria was able to stimulate the growth of several fungal isolates. While in direct physical contact, bacterial strains inhibited the fungal growth. This effect might be attributed to bacterial signal molecules, which also proved to inhibit the germination and growth of scedosporia. In addition, antibacterial agents showed growth-promoting, while corticosteroids exhibited growth inhibitory effect on several
isolates. These data raise the possibility that a
infection or a previously administered antibacterial therapy might be able to increase the chance of a
colonization in a CF lung.
is considered as one of the most frequent agents of mucormycosis. The lack of efficient genetic manipulation tools hampers the characterization of the pathomechanisms and virulence factors of this ...opportunistic pathogenic fungus. Although such techniques have been described for certain species, the performance of targeted mutagenesis and the construction of stable transformants have remained a great challenge in Mucorales fungi. In the present study, a plasmid-free CRISPR-Cas9 system was applied to carry out a targeted gene disruption in
. The described method is based on the non-homologous end-joining repair of the double-strand break caused by the Cas9 enzyme. Using this method, short, one-to-five nucleotide long-targeted deletions could be induced in the orotidine 5'-phosphate decarboxylase gene (
) and, as a result, uracil auxotrophic strains were constructed. These strains are applicable as recipient strains in future gene manipulation studies. As we know, this is the first genetic modification of this clinically relevant fungus.
Mucormycosis is a life-threatening opportunistic infection caused by certain members of the fungal order Mucorales. This infection is associated with high mortality rate, which can reach nearly 100% ...depending on the underlying condition of the patient. Treatment of mucormycosis is challenging because these fungi are intrinsically resistant to most of the routinely used antifungal agents, such as most of the azoles. One possible mechanism of azole resistance is the drug efflux catalyzed by members of the ATP binding cassette (ABC) transporter superfamily. The pleiotropic drug resistance (PDR) transporter subfamily of ABC transporters is the most closely associated to drug resistance. The genome of
encodes eight putative PDR-type transporters. In this study, transcription of the eight
genes has been analyzed after azole treatment. Only the
showed increased transcript level in response to all tested azoles. Deletion of this gene caused increased susceptibility to posaconazole, ravuconazole and isavuconazole and altered growth ability of the mutant. In the
deletion mutant, transcript level of
and
significantly increased. Deletion of
and
was also done to create single and double knock out mutants for the three genes. After deletion of
and
, growth ability of the mutant strains decreased, while deletion of
resulted in increased sensitivity against posaconazole, ravuconazole and isavuconazole. Our result suggests that the regulation of the eight
genes is interconnected and
and
participates in the resistance of the fungus to posaconazole, ravuconazole and isavuconazole.
Phenolic compounds are natural substances that can be obtained from plants. Many of them are potent growth inhibitors of foodborne pathogenic microorganisms, however, phenolic activities against ...spoilage yeasts are rarely studied. In this study, planktonic and biofilm growth, and the adhesion capacity of Pichia anomala, Saccharomyces cerevisiae, Schizosaccharomyces pombe and Debaryomyces hansenii spoilage yeasts were investigated in the presence of hydroxybenzoic acid, hydroxycinnamic acid, stilbene, flavonoid and phenolic aldehyde compounds. The results showed significant anti-yeast properties for many phenolics. Among the tested molecules, cinnamic acid and vanillin exhibited the highest antimicrobial activity with minimum inhibitory concentration (MIC) values from 500 µg/mL to 2 mg/mL. Quercetin, (−)-epicatechin, resveratrol, 4-hydroxybenzaldehyde, p-coumaric acid and ferulic acid were also efficient growth inhibitors for certain yeasts with a MIC of 2 mg/mL. The D. hansenii, P. anomala and S. pombe biofilms were the most sensitive to the phenolics, while the S. cerevisiae biofilm was quite resistant against the activity of the compounds. Fluorescence microscopy revealed disrupted biofilm matrix on glass surfaces in the presence of certain phenolics. Highest antiadhesion activity was registered for cinnamic acid with inhibition effects between 48% and 91%. The active phenolics can be natural interventions against food-contaminating yeasts in future preservative developments.
Certain members of the order
can cause a life-threatening, often-fatal systemic infection called mucormycosis. Mucormycosis has a high mortality rate, which can reach 96 to 100% depending on the ...underlying condition of the patient.
species are intrinsically resistant to most antifungal agents, such as most of the azoles, which makes mucormycosis treatment challenging. The main target of azoles is the lanosterol 14α-demethylase (Erg11), which is responsible for an essential step in the biosynthesis of ergosterol, the main sterol component of the fungal membrane. Mutations in the
gene can be associated with azole resistance; however, resistance can also be mediated by loss of function or mutation of other ergosterol biosynthetic enzymes, such as the sterol 24-C-methyltransferase (Erg6). The genome of Mucor lusitanicus encodes three putative
genes (i.e.,
,
, and
). In this study, the role of
genes in azole resistance of
was analyzed by generating and analyzing knockout mutants constructed using the CRISPR-Cas9 technique. Susceptibility testing of the mutants suggested that one of the three genes,
, plays a crucial role in the azole resistance of
. The sterol composition of
knockout mutants was significantly altered compared to that of the original strain, and it revealed the presence of at least four alternative sterol biosynthesis pathways leading to formation of ergosterol and other alternative, nontoxic sterol products. Dynamic operation of these pathways and the switching of biosynthesis from one to the other in response to azole treatment could significantly contribute to avoiding the effects of azoles by these fungi.
The fungal membrane contains ergosterol instead of cholesterol, which offers a specific point of attack for the defense against pathogenic fungi. Indeed, most antifungal agents target ergosterol or its biosynthesis. Mucormycoses-causing fungi are resistant to most antifungal agents, including most of the azoles. For this reason, the drugs of choice to treat such infections are limited. The exploration of ergosterol biosynthesis is therefore of fundamental importance to understand the azole resistance of mucormycosis-causing fungi and to develop possible new control strategies. Characterization of sterol 24-C-methyltransferase demonstrated its role in the azole resistance and virulence of
Moreover, our experiments suggest that there are at least four alternative pathways for the biosynthesis of sterols in
. Switching between pathways may contribute to the maintenance of azole resistance.
Mucor lusitanicus and some other members of the fungal order Mucorales display the phenomenon of morphological dimorphism. This means that these fungi aerobically produce filamentous hyphae, ...developing a coenocytic mycelium, but they grow in a multipolar yeast-like form under anaerobiosis. Revealing the molecular mechanism of the reversible yeast-hyphal transition can be interesting for both the biotechnological application and in the understanding of the pathomechanism of mucormycosis. In the present study, transcriptomic analyses were carried out after cultivating the fungus either aerobically or anaerobically revealing significant changes in gene expression under the two conditions. In total, 539 differentially expressed genes (FDR < 0.05, |log2FC| ≥ 3) were identified, including 190 upregulated and 349 downregulated transcripts. Within the metabolism-related genes, carbohydrate metabolism was proven to be especially affected. Anaerobiosis also affected the transcription of transporters: among the 14 up- and 42 downregulated transporters, several putative sugar transporters were detected. Moreover, a considerable number of transcripts related to amino acid transport and metabolism, lipid transport and metabolism, and energy production and conversion were proven to be downregulated when the culture had been transferred into an anaerobic atmosphere.
Interaction of the human monocytic cell line, THP-1 with clinical isolates of three
species were examined. Members of this filamentous fungal genus can cause deep mycoses emerging in both ...immunocompromised and immunocompetent patients. It was found that monocytes reacted only to the hyphal form of
. Cells attached to the germ tubes and hyphae and production of elevated levels of interleukin (IL)-8 and IL-10 and a low level of TNF-α were measured. At the same time, monocytes failed to produce IL-6. This monocytic response, especially with the induction of the anti-inflammatory IL-10, correlates well to the observation that
frequently cause chronic infections even in immunocompetent persons. Despite the attachment to the hyphae, monocytes could not reduce the viability of the fungus and the significant decrease in the relative transcript level of HLA-DRA assumes the lack of antigen presentation of the fungus by this cell type.
and
failed to induce the gathering of the cells or the production of any analyzed cytokines. Monocytes did not recognize conidia of
species, even when melanin was lacking in their cell wall.
Abstract
Poster session 3, September 23, 2022, 12:30 PM - 1:30 PM
Mucormycosis is a life-threatening systemic infection caused by certain members of the filamentous fungal order Mucorales (e.g., ...Rhizopus delemar, Lichtheimia corymbifera, and Mucor circinelloides). Mucormycosis is associated with a high mortality rate, which can be nearly 100% depending on the underlying condition of the patient. One of the main risk factors of mucormycosis has been the iron-chelating treatment. Iron is an essential nutrient for both the host and the pathogen. Therefore, organisms developed various strategies to acquire iron from the environment. Three strategies are available to microorganisms to uptake iron from the environment: acidification of the environment, reduction of ferric iron to the more soluble ferrous form, and secretion of soluble iron-chelating molecules. All fungi produce hydroxamate-type siderophore, except Mucorales fungi, which secrete a polycarboxylate siderophore, rhizoferrin. However, they also can utilize hydroxamate siderophores as xenosiderophores.
In the Mucor genome database, one putative sit1 gene encoding a ferrioxamine B transporter, which belongs to the ARN/SIT subfamily of the major facilitator superfamily (MFS), coding was found. In Saccharomyces cerevisiae, Candia albicans, and Aspergillus fumigatus, siderophore-iron chelates are taken up through Arn3/Sit1 transporters. The relative transcript level of sit1 gene was measured after iron-starvation, and different siderophore treatments using quantitative real-time PCR. We have started to create and characterize (growth and germination ability, in vivo virulence assay, etc.) a sit1 knock-out mutant constructed using a CRISPR-Cas9 system.
Sit1 gene showed significantly increased transcript levels using deferoxamine-iron, deferasirox-iron, and enterobactin-iron complexes. The colony diameter of the mutant strain was measured on Blood and Cas agar with (CasFe) or without iron (Cas-Fe). On CasFe agar, the growth ability of the mutant was significantly decreased compared to the control strain. In Galleria mellonella model, disruption of the sit1 gene resulted in decreased virulence. Relative transcript level of the putative rhizoferrin synthase gene (rfs) was measured in the sit1 knock-out mutant, where the gene showed an increased transcript level.
Our result suggested that Sit1 is required for germination and virulence of Mucor lusitanicus and it may influence rhizoferrin production.
This study was supported by the NKFI project K131796 and the grant ITM NKFIA TKP-2021-EGA-28. GN is grateful for the support of the Premium Postdoctoral Fellowship Program of the Hungarian Academy of Sciences (460 050).
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