Characterization of a novel polyextremotolerant fungus, Exophiala viscosa, with insights into its melanin regulation and ecological niche

Black yeasts are polyextremotolerant fungi that contain high amounts of melanin in their cell wall and maintain a primar yeast form. These fungi grow in xeric, nutrient depletes 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 are not well understood. We have isolated 2 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 niche 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 excretes melanin which can potentially provide ultraviolet 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.

Preserved and foreign cartilage interpositional materials for silastic finger joint implant arthroplasty

Cartilage grafts were implanted as interpositional materials (IPMs) around the stems of silicone finger joint prostheses to protect their surfaces from abrasion with the local bone tissue. The knee joints of New Zealand White rabbits were implanted with finger joint prostheses and grafted with preserved auto- and allografts as well as fresh xenografts. Data were obtained after one month and compared to controls that received only the silicone prostheses. The grafting procedures did not cause any variations in joint function or differences in the amount of lipids absorbed by the prosthesis. A thin fibrous capsule formed about the control implants, whereas the capsules of the grafted legs were greater in thickness and area. Gross examination of the implant surfaces, weight analyses, and light microscopic studies of the number of wear particles found in the surrounding tissue capsules all indicated a reduction in prosthetic wear with grafting. The cartilage grafts were surrounded by inflammatory cells and were losing their proteoglycans. As expected, the xenografts exhibited the most degradation. No differences were noted between the preserved grafts. These results indicate that at one month, cartilage has provided protection for early implant motion. The biodegradable graft was being replaced by fibrous connective tissue. Long-term protection needs to be studied in additional experiments.