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Group I introns are small RNAs (250-500 nt) capable of catalyzing their own splicing from the precursor RNA. They are widely distributed across the tree of life and have intricate relationships with their host genomes. In this work, we review its basic structure, self-splicing and its mechanisms of gene mobility. As they are widely found in unicellular eukaryotes, especially fungi, we gathered information regarding their possible impact on the physiology of fungal cells and the possible application of these introns in medical mycology.

The species complexes Cryptococcus neoformans and Cryptococcus gattii are the causative agents of cryptococcosis. Virulence and susceptibility to antifungals may vary within each species according to the fungal genotype. Therefore, specific and easily accessible molecular markers are required to distinguish cryptic species and/or genotypes. Group I introns are potential markers for this purpose because they are polymorphic concerning their presence and sequence. Therefore, in this study, we evaluated the presence of group I introns in the mitochondrial genes cob and cox1 in different Cryptococcus isolates. Additionally, the origin, distribution, and evolution of these introns were investigated by phylogenetic analyses, including previously sequenced introns for the mtLSU gene. Approximately 80.5% of the 36 sequenced introns presented homing endonucleases, and phylogenetic analyses revealed that introns occupying the same insertion site form monophyletic clades. This suggests that they likely share a common ancestor that invaded the site prior to species divergence. There was only one case of heterologous invasion, probably through horizontal transfer to C. decagattii (VGIV genotype) from another fungal species. Our results showed that the C. neoformans complex has fewer introns compared to C. gattii. Additionally, there is significant polymorphism in the presence and size of these elements, both among and within genotypes. As a result, it is impossible to differentiate the cryptic species using a single intron. However, it was possible to differentiate among genotypes within each species complex, by combining PCRs of mtLSU and cox1 introns, for C. neoformans species, and mtLSU and cob introns for C. gattii species.

Background: Cryptococcosis is a common opportunistic infection in patients infected by Human Immunodeficiency Virus (HIV) and is the second leading cause of mortality in Acquired Immunodeficiency Syndrome (AIDS) patients worldwide. The most frequent presentation of cryptococcal infection is subacute meningitis, especially in patients with a CD4+ T Lymphocytes count below 100 cells/μL. However, in severely immunosuppressed individuals Cryptococcus neoformans can infect virtually any human organ, including the bone marrow, which is a rare presentation of cryptococcosis., Case Presentation: A 45-year-old HIV-infected male patient with a CD4+ T lymphocyte count of 26 cells/μL who presented to the emergency department with fever and pancytopenia. Throughout the diagnostic evaluation, the bone marrow aspirate culture yielded encapsulated yeasts in budding, identified as Cryptococcus sp. The bone marrow biopsy revealed a hypocellularity for age and absence of fibrosis. It was observed presence of loosely formed granuloma composed of multinucleated giant cells encompassing rounded yeast like organisms stained with mucicarmine, compatible with Cryptococcus sp. Then, the patient underwent a lumbar puncture to investigate meningitis, although he had no neurological symptoms and neurological examination was normal. The cerebrospinal fluid culture yielded Cryptococcus sp. The species and genotype identification step showed the infection was caused by Cryptococcus neoformans var. grubii (genotype VNI). The patient was initially treated with amphotericin B deoxycholate plus fluconazole for disseminated cryptococcosis, according to guideline recommendations. However, the patient developed acute kidney injury and the treatment was switched for fluconazole monotherapy. The symptoms disappeared completely with recovery of white blood cells and platelets counts. Cerebrospinal fluid cultures for fungi at one and two-weeks of treatment were negative., Conclusions: Bone marrow infection caused by Cryptococcus neoformans is a rare presentation of cryptococcosis. The cryptococcal infection should be included for differential diagnosis in HIV-infected patients with fever and cytopenias, especially when CD4+ T lymphocytes count is below 100 cells/μL.