Biology subjects

Stempinski, P. R.

Publications and source records attributed to Stempinski, P. R..

5 recordsLinked to original sources

bioRxiv2026

Strain-specific thermotolerance, UV-C tolerance, and biofilm formation on clinically relevant plastic substrates in the emerging opportunistic pathogen Rhodotorula mucilaginosa

Rhodotorula mucilaginosa is an emerging opportunistic fungal pathogen increasingly associated with catheter-related bloodstream infections. Although biofilm formation is considered a major virulence trait for R. mucilaginosa, factors contributing to biofilm persistence on medical devices remain poorly understood. Here, we characterized the thermotolerance, biofilm formation, UV resistance, and cell surface hydrophobicity profiles of eight R. mucilaginosa strains representing clinical and non-clinical (laboratory, environmental, and marine mammal) isolates. All strains grew optimally at 30C and exhibited restricted growth at 35C and 37C, although one environmental isolate maintained robust growth at 37C. All strains exhibited moderate to high cell surface hydrophobicity. We then assessed biofilm formation for each strain, including adherence to two different plastic substrates, development of biofilm biomass, comparison of biofilm metabolic activity, and the effects of temperature on biofilm formation. Under static conditions, biofilm biomass of most isolates on 96-well polystyrene plates was greatest at 24C. Clinical isolates generally maintained higher biofilm metabolic activity at 37C than nonclinical isolates, while at lower temperatures, clinical and non-clinical isolates did not differ significantly in metabolic activity. All strains readily formed biofilms on polyurethane intravenous catheters under dynamic conditions, as confirmed by scanning electron microscopy and metabolic activity. While planktonic cells already displayed substantial UV-C tolerance, biofilm-associated cells remained viable following exposure to UV-C doses up to eightfold higher than those that impaired planktonic growth. These findings document differences in thermotolerance and biofilm formation by isolate origin and identify biofilm formation as a major factor promoting persistence of R. mucilaginosa on clinically relevant materials and reduced susceptibility to UV-C sterilization.

microbiology↗

bioRxiv2026

A role for aquaporin (Aqp1) in the control of Cryptococcus neoformans cell morphology

Aquaporins are small, integral membrane channels that facilitate the transport of water across cellular membranes and, in the case of aquaglyceroporins, can also conduct specific neutral solutes, such as glycerol. These proteins are conserved across biological kingdoms, yet their roles in fungal virulence remain relatively understudied. In Cryptococcus neoformans, an opportunistic fungal pathogen, we examined the organisms single aquaporin, Aqp1, and uncovered unanticipated influences on cellular morphology. Loss of Aqp1 resulted in smaller cells, whereas its presence promoted the formation of enlarged titan-like cells. This shift in size was closely linked to intracellular redox physiology. Consequently, the overexpression of the cryptococcal aquaporin increased sensitivity to oxidative stress and led to the largest titan-like cells; antioxidant supplementation suppressed this enlargement, consistent with a ROS-dependent regulatory mechanism. Additionally, Aqp1 overexpression produced vacuolar abnormalities in titan-like cells, suggesting that excessive water influx strained intracellular organization during rapid cell expansion. These findings position Aqp1 at a functional crossroads connecting membrane transport, oxidative balance, and size control, and they support a model in which an aquaporin contributes to the morphological plasticity that allows C. neoformans to adapt to environmental pressures.

microbiology↗

bioRxiv2025

Genetic determinants that permit growth without the core septin Cdc12 in Cryptococcus neoformans

Septins are conserved cytoskeletal GTPases that regulate morphogenesis, cytokinesis, and cell-surface organization in fungi. In most model and pathogenic yeasts, including Saccharomyces cerevisiae and Candida albicans, core septin subunits such as Cdc3 and Cdc12 are essential and their loss results in lethal cytokinetic defects. In Cryptococcus neoformans, by contrast, deletion of CDC12 yields viable cells that grow normally under permissive conditions, raising the question of how this pathogen maintains cell integrity without a functional septin complex. To address this, we compared the transcriptomes of wild-type cells and a cdc12{Delta} mutant. The cdc12{Delta} strain showed a focused set of transcriptional changes, with induction of genes involved in cell wall remodeling, stress-dependent morphogenetic programs, and pathways that promote fitness under compromised cytoskeletal conditions. Genetic analysis of the most highly induced genes uncovered factors that contribute to proliferation in the absence of Cdc12, including a previously uncharacterized aspartic-type endopeptidase that becomes essential when septin function is lost. These findings outline the compensatory circuitry that permits septin-independent growth in C. neoformans and help explain why this pathogen can tolerate septin loss. This intrinsic plasticity highlights C. neoformans as a powerful comparative model for studying the evolution and function of the septin complex.

microbiology↗

bioRxiv2024

The buoyancy of cryptococcal cells and its implications for transport and persistence of Cryptococcus in aqueous environments

Cryptococcus is a genus of saprophytic fungi with global distribution. Two species complexes, C. neoformans and C. gattii, pose health risks to humans and animals. Cryptococcal infections result from inhalation of aerosolized spores and/or desiccated yeasts from terrestrial reservoirs such as soil, trees, and avian guano. More recently, C. gattii has been implicated in infections in marine mammals, suggesting that inhalation of liquid droplets or aerosols from the air-water interface is also an important, yet understudied, mode of respiratory exposure. Water transport has also been suggested to play a role in the spread of C. gattii from tropical to temperate environments. However, the dynamics of fungal survival, persistence, and transport via water have not been fully studied. The size of the cryptococcal capsule was previously shown to reduce cell density and increase buoyancy. Here, we demonstrate that cell buoyancy is also impacted by the salinity of the media in which cells are suspended, with formation of a halocline interface significantly slowing the rate of settling of cryptococcal cells through water, resulting in persistence of C. neoformans within 1 cm of the air-water interface for over 60 min and C. gattii for 4-6 h. Our data also showed that during culture in yeast peptone dextrose media (YPD), polysaccharide accumulating in the supernatant formed a raft that augmented buoyancy and further slowed settling of cryptococcal cells. These findings illustrate new mechanisms by which cryptococcal cells may persist in aquatic environments, with important implications for aqueous transport and pathogen exposure. ImportanceCryptococcosis is a major fungal disease leading to morbidity and mortality worldwide. C. neoformans is a major fungal species of public health concern, causing opportunistic systemic infections in immunocompromised patients. C. gattii was traditionally a tropical pathogen, but in the 1990s emerged in the temperate climates of British Columbia and the Pacific Northwest United States. Outbreaks in these areas also led to the first host record of cryptococcosis in free-ranging cetaceans. C. gattii is particularly concerning as an emerging fungal pathogen due to its capacity to cause clinical disease in immunocompetent patients, its recent spread to a new ecological niche, and its higher resistance to antifungal therapies. Our research defines characteristics that influence transport of cryptococci through water and its persistence at the air-water interface, which improve our understanding of mechanisms for cryptococcal aqueous transport and persistence.

microbiology↗

bioRxiv2024

Proteins associated with Cryptococcus spp. extracellular polysaccharides are implicated in virulence, capsule integrity, and biofilm formation.

Cryptococcus neoformans and Cryptococcus gattii are pathogenic fungi comprising species complexes that are the etiological agents of cryptococcosis. Both fungal species complexes possess a variety of virulence factors that include a polysaccharide capsule, melanin production, enzymes, and the release of polysaccharides. In this study, we characterized the proteins associated with cryptococcal polysaccharides and analyzed their function by studying mutants deficient in their expression. Mass spectrometry analysis of exopolysaccharide fractions revealed 62 proteins, many of which were previously uncharacterized. Analysis of capsule size, structure, and integrity in protein-deficient mutants allowed us to identify four proteins, which we named Extracellular Polysaccharide Related proteins (Exa1-4), and whose absence affected proper capsule assembly and EPS release. In summary, cryptococcal exopolysaccharide is associated with proteins that are implicated in virulence, capsular integrity, and biofilm formation. Our results associated new phenotypes for four previously unknown genes and show that the filtered polysaccharide preparations are a rich source of proteins that can inform capsular assembly, virulence, and immunological studies.

molecular biology↗