Melaninization Reduces Cryptococcus neoformans Susceptibility to Mechanical Stress

Abstract

Melanin is a complex pigment found in various fungal species that is associated with a multitude of protective functions against environmental stresses. In Cryptococcus neoformans, melanin is synthesized from exogenous substrate and deposited in the cell wall. Although melanin is often cited as a protector against mechanical stress, there is a paucity of direct experimental data supporting this claim. To probe whether melanin enhances cellular strength, we used ultrasonic cavitation and French pressure cell press to stress cryptococcal cells and then measured changes in cellular morphology and survival for melanized and non-melanized C. neoformans. Melanized yeast exhibited lower rates of fragmentation and lower decreases in cell area when compared to non-melanized yeast after sonication and French press conditions. Our results indicate that melanization protects against some of the morphologic changes initiated by mechanical energy derived from either sonic cavitation or French press, thus supporting the notion that this pigment provides mechanical strength to fungal cell walls. ImportanceMelanin has been shown from prior experiments in microbiology to be associated with protection against environmental stressors and has often been cited as being associated with mechanical stress protection. However, there is a lack of direct experimentation to confirm this claim. By examining the response of melanized and non-melanized C. neoformans to sonication and French press, we report differences in outcomes dependent not only based on melanization status but also culture age. Such findings have important implications in the design and interpretation of laboratory experiments involving C. neoformans. In addition, uncovering some of melanins mechanical properties promotes further research into fungal melanins applications in healthcare and industry.