Biology subjects

Harris, S. D.

Publications and source records attributed to Harris, S. D..

5 recordsLinked to original sources

bioRxiv2025

Chemical inhibition of asexual development leads to increased ultimate tensile strength in mycelial material.

This study investigates the chemical inhibition of asexual development in Aspergillus nidulans to enhance the mechanical properties of mycelial materials. We hypothesized that suppressing conidiation using the ornithine decarboxylase inhibitor -difluoromethylornithine (DFMO) would increase material strength by inhibiting asexual development, promoting denser hyphal packing. Mycelial materials were grown in DFMO concentrations (0, 0.05, 0.5, and 5 mM), and conidiation and ultimate tensile strength (UTS) were measured. Results showed a dose-dependent reduction in conidiation, with significant decreases at all DFMO levels (P [≤] 0.05). While lower DFMO concentrations (0.05 and 0.5 mM) did not significantly alter UTS, 5 mM DFMO treatment doubled the materials tensile strength compared to controls (P [≤] 0.05). Scanning electron microscopy confirmed reduced developmental structures in DFMO-treated samples, supporting the hypothesis. The non-linear relationship between conidiation suppression and strength improvement suggests additional mechanisms, such as hyphal morphology or cell wall changes, may contribute. These findings demonstrate that chemical modulation of fungal development can rationally tune mycelial material properties, offering a systematic approach for biomaterial engineering.

bioengineering↗

bioRxiv2025

Genetic analysis of pigment production in the fungus Exophiala dermatitidis

Exophiala dermatitidis is a polyextremotolerant black yeast species. E. dermatitidis produces 1,8 dihydroxynaphthalene (DHN) melanin via the Polyketide Synthase 1 (PKS1) pathway enabling it to survive harmful conditions. This study focused on random mutagenesis to obtain albino (alb) and hyper-pigmented (hyp) mutants. Notably, all 17 alb mutants possessed mutations in PKS1 whereas the 133 hyper-pigmented (hyp) mutants harbored mutations impacting a range of functions. Cell morphology and phenotypic assays showed additional differences between the alb and hyp mutants. Strikingly, three of the albino mutants (alb1, alb2, and alb3) were conditional in that despite the presence of mutations in PKS1 they were able to produce melanin upon exposure to different carbon sources. These mutants otherwise shared similar cell morphology and growth patterns with the obligate albinos. No additional shared mutations were found among the conditional albinos. Temperature and UV irradiation assays demonstrated reduced growth of albino mutants at higher temperatures (i.e., 42{degrees}C) and a greater sensitivity to higher doses of UV. Single nucleotide variant (SNVs) calling showed that hyper-pigmented mutants had a greater number of SNVs compared to albino strains. To date this is the first study to generate and characterize conditional albino mutants in E. dermatitidis with the ability to recover melanin production.

genetics↗

bioRxiv2025

Crusty-Pinky: A Novel Polyextremotolerant Fungus and its Methylobacterium Symbionts Could be an Essential Symbiosis for the Biological Soil Crust Consortium

JF2 08-2F Crusty is a novel melanized polyextremotolerant fungus isolated from a biological soil crust, which we believe harbors Methylobacterium spp. endosymbionts, called Pinky. Crusty is capable of utilizing many sources of carbon and nitrogen and is resistant to multiple metals and UV-C due to its melanized cell wall. We were unable to recover a Pinky-free culture of Crusty via usage of antibiotics. However, when exposed to antibiotics that kill or stop the growth of the Pinky, growth of Crusty is significantly stunted, implying that actively growing Pinky symbionts are needed for Crustys optimal growth. The Crusty-Pinky symbiosis also seems to be able to perform active metabolism in carbonless and nitrogenless medium, which we believe is due to Pinkys ability to perform aerobic anoxygenic photosynthesis. Finally, Pinky was identified as being capable of growth stimulation of the algae Chlorella sorokiniana, indicating that Pinky likely produces cytokinins or auxins which Methylobacterium are known for. Features of this symbiosis provide us insight into the ecological roles of these microbes within the biological soil crust.

microbiology↗

bioRxiv2021

Deciphering the potential niche of novel black yeast fungal isolates in a biological soil crust based on genomes, phenotyping, and melanin regulation

Black yeasts are polyextremotolerant fungi that contain high amounts of melanin in their cell wall and maintain a primarily yeast form. These fungi grow in xeric, nutrient deplete environments which implies that they require highly flexible metabolisms and have been suggested to contain the ability to form lichen-like mutualisms with nearby algae and bacteria. However, the exact ecological niche and interactions between these fungi and their surrounding community is not well understood. We have isolated two novel black yeasts from the genus Exophiala that were recovered from dryland biological soil crusts. Despite notable differences in colony and cellular morphology, both fungi appear to be members of the same species, which has been named Exophiala viscosa (i.e., E. viscosa JF 03-3 Goopy and E. viscosa JF 03-4F Slimy). A combination of whole genome sequencing, phenotypic experiments, and melanin regulation experiments have been performed on these isolates to fully characterize these fungi and help decipher their fundamental niches within the biological soil crust consortium. Our results reveal that E. viscosa is capable of utilizing a wide variety of carbon and nitrogen sources potentially derived from symbiotic microbes, can withstand many forms of abiotic stresses, and excrete melanin that can potentially provide UV resistance to the biological soil crust community. Besides the identification of a novel species within the genus Exophiala, our study also provides new insight into the regulation of melanin production in polyextremotolerant fungi.

microbiology↗

bioRxiv2021

Micafungin-induced Cell Wall Damage Stimulates Microcycle Conidiation in Aspergillus nidulans

Fungal cell wall receptors relay messages about the state of the cell wall to the nucleus through the Cell Wall Integrity Signaling (CWIS) pathway. The ultimate role of the CWIS pathway is to coordinate repair of cell wall damage and to restore normal hyphal growth. Echinocandins such as micafungin represent a class of antifungals that trigger cell wall damage by affecting synthesis of {beta}-glucans, filamentous fungis response to these antifungals are fundamentally unknown. To obtain a better understanding of the dynamics of the CWIS response and its multiple effects, we have coupled dynamic transcriptome analysis with morphological studies of Aspergillus nidulans hyphae responding to micafungin. Our results reveal that expression of the master regulator of asexual development, BrlA, is induced by micafungin exposure. Further study showed that micafungin elicits microcycle conidiation in a BrlA-dependent manner, and that this response is abolished in the absence of MpkA. Our results suggest that microcycle conidiation may be a general response to cell wall perturbation which in some cases would enable fungi to tolerate or survive otherwise lethal damage.

molecular biology↗