Identification and characterization of a sulfite reductase gene and new insights regarding the sulfur-containing amino acid metabolism in the basidiomycetous yeast Cryptococcus neoformans

Modification of Yarrowia lipolytica via metabolic engineering for effective remediation of heavy metals from wastewater

With the increasing demand for heavy metals due to the advancement of industrial activities, large proportions of heavy metals have been discharged into aquatic ecosystems, causing serious harm to human health and the environment. Existing physical and chemical methods for recovering heavy metals from wastewater encounter challenges, such as low efficiency, high processing costs, and potential secondary pollution. In this study, we developed a novel approach by engineering the endogenous sulphur metabolic pathway of Yarrowia lipolytica, providing it with the ability to produce approximately 550 ppm of sulphide. Subsequently, sulphide-producing Y. lipolytica was used for the first time in heavy metal remediation. The engineered strain exhibited a high capacity to remove various heavy metals, especially achieving over 90 % for cadmium (Cd), copper (Cu) and lead (Pb). This capacity was consistent when applied to both synthetic and actual wastewater samples. Microscopic analyses revealed that sulphide-mediated biological precipitation of metal sulphides on the cell surface is responsible for their removal. Our findings demonstrate that sulphide-producing yeasts are a robust and effective bioremediation strategy for heavy metals, showing great potential for future heavy metal pollution remediation practices.

LOX1- and PLP1-dependent transcriptional reprogramming is essential for injury-induced conidiophore development in a filamentous fungus

IMPORTANCE

In addition to being considered a biocontrol agent, the fungus Trichoderma atroviride is a relevant model for studying mechanisms of response to injury conserved in plants and animals that opens a new landscape in relation to regeneration and cell differentiation mechanisms. Here, we reveal the co-functionality of a lipoxygenase and a patatin-like phospholipase co-expressed in response to wounding in fungi. This pair of enzymes produces oxidized lipids that can function as signaling molecules or oxidative stress signals that, in ascomycetes, induce asexual development. Furthermore, we determined that both genes participate in the regulation of the synthesis of 13-HODE and the establishment of the physiological responses necessary for the formation of reproductive aerial mycelium ultimately leading to asexual development. Our results suggest an injury-induced pathway to produce oxylipins and uncovered physiological mechanisms regulated by LOX1 and PLP1 to induce conidiation, opening new hypotheses for the novo regeneration mechanisms of filamentous fungi.

ATP sulfurylase atypical leucine zipper interacts with Cys3 and calcineurin A in the regulation of sulfur amino acid biosynthesis in Cryptococcus neoformans

Fungal pathogens are a major cause of death, especially among immunocompromised patients. Therapies against invasive fungal infections are restricted to a few antifungals; therefore, novel therapies are necessary. Nutritional signaling and regulation are important for pathogen establishment in the host. In Cryptococcus neoformans, the causal agent of fungal meningitis, amino acid uptake and biosynthesis are major aspects of nutritional adaptation. Disruptions in these pathways lead to virulence attenuation in an animal model of infection, especially for sulfur uptake and sulfur amino acid biosynthesis. Deletion of Cys3, the main transcription factor that controls these pathways, is the most deleterious gene knockout in vitro and in vivo, making it an important target for further application. Previously, we demonstrated that Cys3 is part of a protein complex, including calcineurin, which is necessary to maintain high Cys3 protein levels during sulfur uptake and sulfur amino acid biosynthesis. In the current study, other aspects of Cys3 regulation are explored. Two lines of evidence suggest that C. neoformans Cys3 does not interact with the F-box WD40 protein annotated as Met30, indicating another protein mediates Cys3 ubiquitin degradation. However, we found another level of Cys3 regulation, which involves protein interactions between Cys3 and ATP sulfurylase (MET3 gene). We show that an atypical leucine zipper at the N-terminus of ATP sulfurylase is essential for physical interaction with Cys3 and calcineurin. Our data suggests that Cys3 and ATP sulfurylase interact to regulate Cys3 transcriptional activity. This work evidences the complexity involved in the regulation of a transcription factor essential for the sulfur metabolism, which is a biological process important to nutritional adaptation, oxidative stress response, nucleic acid stability, and methylation. This information may be useful in designing novel therapies against fungal infections.

Adenylyl-Sulfate Kinase (Met14)-Dependent Cysteine and Methionine Biosynthesis Pathways Contribute Distinctively to Pathobiological Processes in Cryptococcus neoformans

Blocking of nutrient uptake and amino acid biosynthesis are considered potential targets for next-generation antifungal drugs against pathogenic fungi, including Cryptococcus neoformans. In this regard, the sulfate assimilation pathway is particularly attractive, as it is only present in eukaryotes such as plants and fungi, yet not in mammals. Here, we demonstrated that the adenylyl sulfate kinase (Met14) in the sulfate assimilation pathway is not essential yet is required for the viability of C. neoformans due to its involvement in biosynthesis of two sulfur-containing amino acids, cysteine and methionine. Met14-dependent cysteine and methionine biosynthesis was found to significantly contribute to a diverse range of pathobiological processes in C. neoformans. Met14-dependent cysteine rather than methionine biosynthesis was also found to play pivotal roles in cell growth and tolerance to environmental stresses and antifungal drugs. In contrast, the Met14-dependent methionine biosynthesis was found to be more important than cysteine biosynthesis for the production of major cryptococcal virulence factors of melanin pigments and polysaccharide capsules. Finally, we also found that despite its attenuated virulence in an insect model, Galleria mellonella, the met14Δ mutant yielded no difference in virulence in a murine model of systemic cryptococcosis. Hence, clinical inhibition of Met14-dependent amino acid biosynthetic pathways may not be advantageous for the treatment of systemic cryptococcosis. IMPORTANCE Current antifungal drugs have several limitations, such as drug resistance, severe side effects, and a narrow spectrum. Therefore, novel antifungal targets are urgently needed. To this end, fungal sulfur amino acid biosynthetic pathways are considered potential targets for development of new antifungal agents. Here, we demonstrated that Met14 in the sulfate assimilation pathway promotes growth, stress response, and virulence factor production in C. neoformans via synthesis of sulfur-containing amino acids methionine and cysteine. Met14-dependent cysteine rather than methionine synthesis was found to be critical for growth and stress responses, whereas Met14-dependent methionine synthesis was more important for the production of antiphagocytic capsules and antioxidant melanin in C. neoformans. Surprisingly, deletion of the MET14 gene was found to attenuate cryptococcal virulence in an insect model, yet not in a murine model. Collectively, our results showed that Met14-dependent cysteine and methionine biosynthesis play roles that are distinct from each other in C. neoformans. Moreover, Met14 is unlikely to be a suitable anticryptococcal drug target.

β-Glucan Enhances the Biocontrol Efficacy of Marine Yeast Scheffersomyeces spartinae W9 against Botrytis cinerea in Strawberries

The marine yeast Scheffersomyeces spartinae W9 is a promising biocontrol agent for gray mold caused by Botrytis cinerea in strawberries. Improving the biocontrol efficacy of S. spartinae W9 is necessary for its commercial application. In this study, different concentrations of β-glucan were added to the culture medium to evaluate its effect on the biocontrol efficacy of S. spartinae W9. The results showed that 0.1% β-glucan could increase the biocontrol effect of S. spartinae W9 against B. cinerea in strawberries and in vitro. We found that adding 0.1% β-glucan to the culture medium promoted the growth of S. spartinae W9 in wounds of strawberries, enhanced biofilm formation ability, and secreted more β-1,3-glucanase. In addition, 0.1% β-glucan increased the survival rate of S. spartinae W9 under oxidative, thermal, osmotic, and plasma membrane stressors. Transcriptome analysis revealed 188 differential expressed genes in S. spartinae W9 cultured with or without 0.1% β-glucan, including 120 upregulated and 68 downregulated genes. The upregulated genes were associated with stress response, cell wall formation, energy production, growth, and reproduction. Thus, culturing with 0.1% β-glucan is an effective way to improve the biocontrol ability of S. spartinae W9 against gray mold in strawberries.

Cryptococcus neoformans MET5 Gene is not Essential for Virulence in the Silkworm Infection Model

The involvement of the MET5 gene in virulence of Cryptococcus neoformans was examined using the silkworm Bombyx mori infection model. In the virulence assay, the met5Δ mutant showed virulence not significantly different from the wild-type strain, suggesting that the MET5 gene is not essential for full virulence of C. neoformans. The effect of silkworm hemolymph on the survival of the met5Δ mutant was also tested. The C. neoformans met5Δ strain incubated in the silkworm hemolymph for five days remained viable, suggesting that silkworm hemolymph supports survival of the met5Δ strain.