Species of the Sporothrix complex are the etiological agents of sporotrichosis, an important subcutaneous mycosis with several clinical forms and an increasing incidence around the world that affects humans and other mammals. The immunological mechanisms involved in the prevention and control of this mycosis are not entirely understood. Many reports have suggested that cell-mediated immunity has an essential role in the development of the disease, being the primary response controlling it, while only recent data supports that the humoral response is essential for the appropriate control. This mycosis is a challenge for diagnosis since the culture and isolation of the organism are time-consuming and complicated; reasons that have led to the study of fungus antigenic molecules capable of generating a detectable humoral response. The treatment for this disease includes the use of several antifungal drugs like itraconazole, amphotericin B, caspofungin, fluconazole, and the combination between them among others such as the extract of Vismia guianensis.

Fungal infections are a serious and increasing threat for human health, and one of the most frequent etiological agents for systemic mycoses is Candida spp. The gold standard to assess Candida virulence is the mouse model of systemic candidiasis, a restrictive, expensive, and time-consuming approach; therefore, invertebrate models have been proposed as alternatives. Galleria mellonella larvae have several traits that make them good candidates to study the fungal virulence. Here, we showed that a reduction in circulating hemocytes, increased melanin production, phenoloxidase, and lactate dehydrogenase activities were observed at 12 and 24 h postinoculation of highly virulent Candidatropicalis strains, while minimal changes in these parameters were observed in low-virulent strains. Similarly, the most virulent species Candida albicans, Candida tropicalis, Candida auris, Candida parapsilosis, and Candida orthopsilosis have led to significant changes in those parameters; while the low virulent species Candida guilliermondii, Candida krusei, and Candida metapsilosis induced modest variations in these immunological and cytotoxicity parameters. Since changes in circulating hemocytes, melanin production, phenoloxidase and lactate dehydrogenase activities showed a correlation with the larval median survival rates at 12 and 24 h postinoculation, we proposed them as candidates for early virulence predictors in G. mellonella.

The ongoing COVID-19 pandemic has quickly become a health threat worldwide, with high mortality and morbidity among patients with comorbidities. This viral infection promotes the perfect setting in patients for the development of opportunistic infections, such as those caused by fungi. Mucormycosis, a rare but deadly fungal infection, has recently increased its incidence, especially in endemic areas, since the onset of the pandemic. COVID-19-associated mucormycosis is an important complication of the pandemic because it is a mycosis hard to diagnose and treat, causing concern among COVID-19-infected patients and even in the already recovered population. The risk factors for the development of mucormycosis in these patients are related to the damage caused by the SARS-CoV-2 itself, the patient’s overstimulated immune response, and the therapy used to treat COVID-19, causing alterations such as hyperglycemia, acidosis, endothelial and lung damage, and immunosuppression. In this review, the molecular aspects of mucormycosis and the main risk factors for the development of COVID-19-associated mucormycosis are explained to understand this virus–fungi–host interaction and highlight the importance of this neglected mycosis.

Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa are etiological agents of sporotrichosis, a human subcutaneous mycosis. Although the protocols to evaluate Sporothrix virulence in animal models are well described, the cell preparation before inoculation is not standardized, and several culturing media are used to grow yeast-like cells. Here, we found that carbon or nitrogen limitation during fungal cell preparation negatively impacted the ability of S. schenckii and S. brasiliensis to kill Galleria mellonella larvae, but not S. globosa. The fungal growth conditions associated with the short median survival of animals were accompanied by increased hemocyte countings, phenoloxidase activity, and cytotoxicity. The fungal growth under carbon or nitrogen limitation also affected the cell wall composition of both S. schenckii and S. brasiliensis and showed increased exposure of β-1,3-glucan at the cell surface, while those growing conditions had a minimal impact on the S.globosa wall, which had higher levels of this polysaccharide exposed on the wall regardless of the culture condition. This polysaccharide exposure was linked to the increased ability of insect hemocytes to uptake fungal cells, suggesting that this is one of the mechanisms behind the lower virulence of S.globosa or cells from the other species grown in carbon or nitrogen limitation.

Moonlighting proteins represent an intriguing area of cell biology, due to their ability to perform two or more unrelated functions in one or many cellular compartments. These proteins have been described in all kingdoms of life and are usually constitutively expressed and conserved proteins with housekeeping functions. Although widely studied in pathogenic bacteria, the information about these proteins in pathogenic fungi is scarce, but there are some reports of their functions in the etiological agents of the main human mycoses, such as Candida spp., Paracoccidioides brasiliensis, Histoplasma capsulatum, Aspergillus fumigatus, Cryptococcus neoformans, and Sporothrix schenckii. In these fungi, most of the described moonlighting proteins are metabolic enzymes, such as enolase and glyceraldehyde-3-phosphate dehydrogenase; chaperones, transcription factors, and redox response proteins, such as peroxiredoxin and catalase, which moonlight at the cell surface and perform virulence-related processes, contributing to immune evasion, adhesions, invasion, and dissemination to host cells and tissues. All moonlighting proteins and their functions described in this review highlight the limited information about this biological aspect in pathogenic fungi, representing this a relevant opportunity area that will contribute to expanding our current knowledge of these organisms’ pathogenesis.

Sporothrixschenckii is one of the etiological agents of sporotrichosis, a worldwide-distributed subcutaneous mycosis. Its cell wall contains a glycoconjugate composed of rhamnose, mannose, glucuronic acid, and proteins, named peptidorhamnomannan, which harbors important Sporothrix-specific immunogenic epitopes. Although the peptidorhamnomannan carbohydrate moiety has been extensively studied, thus far, little is known about the protein core. Here, using LC-MS/MS, we analyzed the S.schenckii peptidorhamnomannan peptide fraction and generated mass signals of 325 proteins, most of them likely to be moonlighting proteins. Among the identified proteins, chaperonin GroEL/Hsp60 and the uncharacterized protein Pap1 were selected for further analysis. Both proteins were heterologously expressed in bacteria, and they showed adhesive properties to the extracellular matrix proteins laminin, elastin, fibrinogen, and fibronectin, although Pap1 also was bound to type-I and type-II collagen. The inoculation of concentrations higher than 40 μg of these proteins, separately, increased immune effectors in the hemolymph of Galleriamellonella larvae and protected animals from an S.schenckii lethal challenge. These observations were confirmed when yeast-like cells, pre-incubated with anti-rHsp60 or anti-rPap1 antibodies were used to inoculate larvae. The animals inoculated with pretreated cells showed increased survival rates when compared to the control groups. In conclusion, we report that Hsp60 and Pap1 are part of the cell wall peptidorhamnomannan, can bind extracellular matrix components, and contribute to the S.schenckii virulence. To our knowledge, this is the first report about moonlighting protein in the S.schenckii cell wall with an important role during the pathogen–host interaction.