Responses of Sporothrix globosa to the cell wall perturbing agents Congo Red and Calcofluor White

Importance of benzoyltransferase GcnE and lysine benzoylation of alcohol dehydrogenase AdhB in pathogenesis and aflatoxin production in Aspergillus flavus

Lysine benzoylation (Kbz) is a newly identified post-translational modification associated with active transcription and metabolism in eukaryotes. However, whether Kbz exists in pathogenic fungi and its function remains unknown. Here, we demonstrated for the first time that Kbz is present in Aspergillus flavus and identified 60 benzoylated sites on 46 benzoylated proteins by global benzoylome analysis. Our data demonstrated that alcohol dehydrogenase B (AdhB) is regulated by benzoylation on lysine 321 (K321), and mutations of Kbz site in AdhB significantly reduced the alcohol dehydrogenase activity in vivo and in vitro. Both adhB deletion mutant and benzoylated site mutants (K321R and K321A) exhibited similar phenotype, including decreased conidiation and seed colonization, increased sclerotia formation and aflatoxin production, and more sensitive to cell wall damage stress. We also found that GcnE has benzoyltransferase activity in vitro and in vivo, and its repression leads to decreased Kbz level and enzymatic activity of AdhB. The catalytic site E139 is important for the benzoyltransferase function of GcnE. Our study uncovers a previously unknown mechanism by which benzoylation regulates AdhB activity to affect the development, secondary metabolism, pathogenicity, and stress response of A. flavus. Meanwhile, it points out the important role of Kbz in the pathogenicity of pathogenic fungi.IMPORTANCEAspergillus flavus is a ubiquitous opportunistic pathogen of plants and animals, which produces carcinogenic and toxic secondary metabolite aflatoxin. A. flavus and aflatoxin contamination have emerged as a global food safety concern. Currently, post-translational modification plays crucial modulatory roles in the fungal development and virulence, but the role of benzoylation in fungal pathogenicity remains undetermined, which limits the development of prevention and control technique. Here, we first identified 46 benzoylated proteins in A. flavus, and found that benzoyltransferase GcnE exerted effects on pathogenicity and aflatoxin production by regulating the benzoylation of AdhB. This finding not only provided valuable information for prevention and control of A. flavus contamination, but also offered basic knowledge for investigation of the regulation mechanism of secondary metabolism in other fungi.

A novel hypovirulence-associated Hadaka virus 1 (HadV1-LA6) in Fusarium oxysporum f. sp. cubense

Fusarium oxysporum f. sp. cubense (Foc) poses a significant threat to banana crops as a lethal fungal pathogen. The global spread of Foc underscores the formidable challenges associated with traditional management methods in combating this pathogen. This study delves into the hypovirulence-associated mycovirus in Foc. From Foc strain LA6, we isolated and characterized a novel member of the Hadakaviridae family, named Hadaka virus 1 strain LA6 (HadV1-LA6). HadV1-LA6 comprises 10 genomic RNA segments, with RNA1 to RNA7 sharing 80.9%-95.0% amino acid sequence identity with known HadV1-7n, while RNA8 to RNA10 display significantly lower identity. HadV1-LA6 demonstrates horizontal transmission capabilities in an all-or-none fashion between different Foc strains via coculturing. Phenotypic comparisons highlight that HadV1-LA6 significantly reduces the growth rates of its host fungus under cell wall stress and oxidative stress conditions. Importantly, HadV1-LA6 attenuates Foc's virulence in detached leaves and banana plants. This study represents the first introduction of a novel hypovirulence-associated Hadaka virus 1 in Foc.IMPORTANCEFusarium wilt of banana (FWB) is a severe fungal disease caused by soil-borne Fusarium oxysporum f. sp. cubense (Foc). Among various strategies, biocontrol emerges as a safe, ecologically friendly, and cost-effective approach to managing FWB. In this study, we focus on exploring the potential of a novel hypovirulent member of hadakavirid, HadV1-LA6. Previous reports suggest that HadV1 shows no apparent effect on the host. However, through phenotypic assessments, we demonstrate that HadV1-LA6 significantly impedes the growth rates of its host fungus under stress conditions. More importantly, HadV1-LA6 exhibits a remarkable capacity to attenuate Foc's virulence in detached leaves and banana plants. Furthermore, HadV1-LA6 could be horizontally transmitted between different Foc strains, presenting a promising resource for revealing the molecular mechanism of the interaction between Hadaka virus 1 and its host.

Influence of Zinc on Histoplasma capsulatum Planktonic and Biofilm Cells

Histoplasma capsulatum causes a fungal respiratory disease. Some studies suggest that the fungus requires zinc to consolidate the infection. This study aimed to investigate the influence of zinc and the metal chelator TPEN on the growth of Histoplasma in planktonic and biofilm forms. The results showed that zinc increased the metabolic activity, cell density, and cell viability of planktonic growth. Similarly, there was an increase in biofilm metabolic activity but no increase in biomass or extracellular matrix production. N'-N,N,N,N-tetrakis-2-pyridylmethylethane-1,2 diamine (TPEN) dramatically reduced the same parameters in the planktonic form and resulted in a decrease in metabolic activity, biomass, and extracellular matrix production for the biofilm form. Therefore, the unprecedented observations in this study highlight the importance of zinc ions for the growth, development, and proliferation of H. capsulatum cells and provide new insights into the role of metal ions for biofilm formation in the dimorphic fungus Histoplasma, which could be a potential therapeutic strategy.

Fungal Glycosidases in Sporothrix Species and Candida albicans

Glycoside hydrolases (GHs) are enzymes that participate in many biological processes of fungi and other organisms by hydrolyzing glycosidic linkages in glycosides. They play fundamental roles in the degradation of carbohydrates and the assembly of glycoproteins and are important subjects of studies in molecular biology and biochemistry. Based on amino acid sequence similarities and 3-dimensional structures in the carbohydrate-active enzyme (CAZy), they have been classified in 171 families. Members of some of these families also exhibit the activity of trans-glycosydase or glycosyl transferase (GT), i.e., they create a new glycosidic bond in a substrate instead of breaking it. Fungal glycosidases are important for virulence by aiding tissue adhesion and colonization, nutrition, immune evasion, biofilm formation, toxin release, and antibiotic resistance. Here, we review fungal glycosidases with a particular emphasis on Sporothrix species and C. albicans, two well-recognized human pathogens. Covered issues include a brief account of Sporothrix, sporotrichosis, the different types of glycosidases, their substrates, and mechanism of action, recent advances in their identification and characterization, their potential biotechnological applications, and the limitations and challenges of their study given the rather poor available information.

Cell compensatory responses of fungi to damage of the cell wall induced by Calcofluor White and Congo Red with emphasis on Sporothrix schenckii and Sporothrix globosa. A review

The cell wall (CW) of fungi exhibits a complex structure and a characteristic chemical composition consisting almost entirely of interacting crystalline and amorphous polysaccharides. These are synthesized by a number of sugar polymerases and depolymerases encoded by a high proportion of the fungal genome (for instance, 20% in Saccharomyces cerevisiae). These enzymes act in an exquisitely coordinated process to assemble the tridimensional and the functional structure of the wall. Apart from playing a critical role in morphogenesis, cell protection, viability and pathogenesis, the CW represents a potential target for antifungals as most of its constituents do not exist in humans. Chitin, β-glucans and cellulose are the most frequent crystalline polymers found in the fungal CW. The hexosamine biosynthesis pathway (HBP) is critical for CW elaboration. Also known as the Leloir pathway, this pathway ends with the formation of UDP-N-GlcNAc after four enzymatic steps that start with fructose-6-phosphate and L-glutamine in a short deviation of glycolysis. This activated aminosugar is used for the synthesis of a large variety of biomacromolecules in a vast number of organisms including bacteria, fungi, insects, crustaceans and mammalian cells. The first reaction of the HBP is catalyzed by GlcN-6-P synthase (L-glutamine:D-fructose-6-phosphate amidotransferase; EC 2.6.1.16), a critical enzyme that has been considered as a potential target for antifungals. The enzyme regulates the amount of cell UDP-N-GlcNAc and in eukaryotes is feedback inhibited by the activated aminosugar and other factors. The native and recombinant forms of GlcN-6-P synthase has been purified and characterized from both prokaryotic and eukaryotic organisms and demonstrated its critical role in CW remodeling and morphogenesis after exposure of some fungi to agents that stress the cell surface by interacting with wall polymers. This review deals with some of the cell compensatory responses of fungi to wall damage induced by Congo Red and Calcofluor White.