We describe a classic case of nasal rhinosporidiosis in a woman who resided in Johannesburg, South Africa, but originated from a rural area in Eastern Cape Province. We confirmed histologic diagnosis using PCR testing and compared details with those from records on 17 other cases from South Africa.

Although there has been long-standing recognition that stimuli-induced cytosolic pH alterations coincide with changes in calcium ion (Ca2+) levels, the interdependence between protons (H+) and Ca2+ remains poorly understood. We addressed this topic using the light-gated channelrhodopsin HcKCR2 from the pseudofungus Hyphochytrium catenoides, which operates as a H+ conductive, Ca2+ impermeable ion channel on the plasma membrane of plant cells. Light activation of HcKCR2 in Arabidopsis guard cells evokes a transient cytoplasmic acidification that sparks Ca2+ release from the endoplasmic reticulum. A H+-induced cytosolic Ca2+ signal results in membrane depolarization through the activation of Ca2+-dependent SLAC1/SLAH3 anion channels, which enabled us to remotely control stomatal movement. Our study suggests a H+-induced Ca2+ release mechanism in plant cells and establishes HcKCR2 as a tool to dissect the molecular basis of plant intracellular pH and Ca2+ signaling.

Kalium channelrhodopsin 1 from Hyphochytrium catenoides (HcKCR1) is the first discovered natural light-gated ion channel that shows higher selectivity to K+ than to Na+ and therefore is used to silence neurons with light (optogenetics). Replacement of the conserved cysteine residue in the transmembrane helix 3 (Cys110) with alanine or threonine results in a >1,000-fold decrease in the channel closing rate. The phenotype of the corresponding mutants in channelrhodopsin 2 is attributed to breaking of a specific interhelical hydrogen bond (the \"DC gate\"). Unlike CrChR2 and other ChRs with long distance \"DC gates\", the HcKCR1 structure does not reveal any hydrogen bonding partners to Cys110, indicating that the mutant phenotype is likely caused by disruption of direct interaction between this residue and the chromophore. In HcKCR1_C110A, fast photochemical conversions corresponding to channel gating were followed by dramatically slower absorption changes. Full recovery of the unphotolyzed state in HcKCR1_C110A was extremely slow with two time constants 5.2 and 70 min. Analysis of the light-minus-dark difference spectra during these slow processes revealed accumulation of at least four spectrally distinct blue light-absorbing photocycle intermediates, L, M1 and M2, and a UV light-absorbing form, typical of bacteriorhodopsin-like channelrhodopsins from cryptophytes. Our results contribute to better understanding of the mechanistic links between the chromophore photochemistry and channel conductance, and provide the basis for using HcKCR1_C110A as an optogenetic tool.

KCR channelrhodopsins (K+-selective light-gated ion channels) have received attention as potential inhibitory optogenetic tools but more broadly pose a fundamental mystery regarding how their K+ selectivity is achieved. Here, we present 2.5-2.7 Å cryo-electron microscopy structures of HcKCR1 and HcKCR2 and of a structure-guided mutant with enhanced K+ selectivity. Structural, electrophysiological, computational, spectroscopic, and biochemical analyses reveal a distinctive mechanism for K+ selectivity; rather than forming the symmetrical filter of canonical K+ channels achieving both selectivity and dehydration, instead, three extracellular-vestibule residues within each monomer form a flexible asymmetric selectivity gate, while a distinct dehydration pathway extends intracellularly. Structural comparisons reveal a retinal-binding pocket that induces retinal rotation (accounting for HcKCR1/HcKCR2 spectral differences), and design of corresponding KCR variants with increased K+ selectivity (KALI-1/KALI-2) provides key advantages for optogenetic inhibition in vitro and in vivo. Thus, discovery of a mechanism for ion-channel K+ selectivity also provides a framework for next-generation optogenetics.

Rhinosporidiosis is a chronic granulomatous disease caused by Rhinosporidium seeberi commonly affecting nasal mucosa, conjunctiva, and urethra. Subcutaneous tumor nodule presentation is rare and often mimics as sarcoma. Such tumoral rhinosporidiosis has been reported rarely. This report describes a 60-year male who presented with a solitary, firm, nontender swelling in posterior aspect of right leg with an ulcer and mimicking clinically as soft tissue sarcoma. Histopathology was diagnostic. Surgical excision was found to be useful.

Rhinosporidiosis is a chronic mucocutaneous granulomatous disease caused by Rhinosporidium seeberi, commonly affecting the nose and nasopharynx. Endobronchial involvement is of rare occurrence but can pose challenging problems for diagnosis, surgical excision and anaesthetic management. We report a 40-year-old man with a history of recurrent nasal rhinosporidiosis who presented with unilateral nasal obstruction, cough, shortness of breath and a radiological feature of left lung collapse. Eight years since the last surgery, he presented with a recurrent lesion in the nose with concurrent endobronchial involvement. The patient underwent excision of the nasal and the endobronchial lesion successfully under general anaesthesia without any complication and good symptomatic improvement. The clinical presentation and the management of endobronchial rhinosporidiosis are discussed here. The surgical difficulties faced during the procedure are highlighted.

BACKGROUND: Rhinosporidiosis is a chronic granulomatous disease of the nose caused by Rhinosporidium seeberi. The disease is largely non-amenable to medical therapy and shows high recurrence rates requiring patients to undergo multiple surgeries often resulting in increased morbidity.
OBJECTIVE: To analyse the epidemiological, clinical, histopathological characteristics, treatment and outcome in rhinosporidiosis and to identify factors which predispose to recurrence of the disease.
METHODS: Retrospective analysis of data of all patients with a diagnosis of rhinosporidiosis confirmed by histopathology at a tertiary care hospital from 2015 to 2019.
RESULTS: There were 42 patients, 40 males and two females, with a mean age of 37.37 years. Disease showed bilateral involvement in 17 (40.48%) patients. Nineteen (45.24%) patients had more than two sites involved at initial presentation. Most patients had nasal cavity involvement followed by nasopharynx. Among the 28 patients who had a follow-up, 12 showed recurrent disease. However, 21 patients were disease free following a revision excision. Involvement of more than two sites was an independent significant factor for recurrence. On univariate analysis, other factors which showed statistically significant odds of developing recurrence were previous surgery (p = .054), involvement of nasal septum (p = .022), middle turbinate (p = .024), nasopharynx (p = .049) and posterior pharyngeal wall (p = .05). Factors which showed significantly less likelihood of developing a recurrence included patients who had less than 12 months duration from first symptom to intervention (p = .016), involvement of less than two sites (p = .0003) and unilateral disease (p = .019).
CONCLUSIONS: Early intervention in rhinosporidiosis especially when the disease is unilateral and involves less than two sites improves the outcome.

Rhinosporidiosis, an infectious granulomatous disease, is seldom encountered in the United States. We present a case of rhinosporidiosis in a 26-year-old man, who presented with an unusual mass in his nasal cavity. Suspicion for rhinosporidiosis was high due to the patient\'s travel and activity history. After imaging and proper diagnosis, surgery was performed to excise the lesion. As international travel resumes during the COVID-19 pandemic, the potential for encountering this rare organism is heightened.

Rhinosporidiosis is a chronic mucocutaneous granulomatous disease caused by Rhinosporidium seeberi, involving primarily the nose and nasopharynx. Very rarely, the disease can affect the lacrimal sac. Here we report a 35-year-old male patient who had rhinosporidial involvement of the nose 5 years ago, for which he underwent endoscopic nasal surgery. Five years after the excision of the nasal mass, he presented with lacrimal sac involvement. The clinical presentation and the management of lacrimal sac rhinosporidiosis are discussed here.

Rhinosporidium seeberi (R. seeberi) causes rhinosporidiosis, which is manifested as tumor-like polyps developing primarily in the nostrils and conjunctiva in human and animals. This disease is characterized by the presence of large, round-shaped mature stage and small endospores with resistance to culturing. R. seeberi was first reported in 1900 as a sporozoan parasite, but later classified as a lower fungi, although its morphological similarity with aquatic parasites were also noticed. According to 18S small-subunit ribosomal DNA sequencing, R. seeberi belongs to a group of fish parasite DRIP clade located between the animal and fungal divergence. Histological examination is thus necessary for the definitive diagnosis of rhinosporidiosis, and the first line of treatment is usually total surgical excision and electro-cauterization of the polyp base. Among the drug therapies attempted, remission has been reported in some patients who received only Dapson treatment. This disease is endemic across India, Pakistan and Sri Lanka and occurs sporadically in other parts of The World with a common history of patients bathing in stagnant water. An outbreak in Serbia during 1992-1995 and 5 rhinosporidiosis cases from Turkey have been reported until date. Considering that rhinosporidiosis is associated with exposure to water and the agent belongs to a branch of aquatic parasites, it has been proposed that aquatic animals are the natural hosts and that the mammalian hosts acquire infection by contacting contaminated water. Therefore, there is a need for the investigation of the infection in fish besides mammalian animals as reservoirs as well as to conduct screening of antiparasitic drugs with infected fish or infected cell lines with the nearest phylogenetic relatives of R. seeberi.