Effects of Agitation-Induced Shear Stress on Curvularia lunata Branching Morphology

Author(s):

Kelsey Gray, Jordan Baumbach, Matthew Servinsky, and Bryn Adams

Abstract:

This study investigates the morphological control of the melanin-producing fungus Curvularia lunata to support the development of melanized biomaterials for advanced military applications. While researchers seek to dictate morphology using agitation-induced shear stress, the quantitative relationships governing these dynamics remain poorly characterized. C. lunata was cultivated across various agitation speeds (50–250 rpm), flask sizes (250 and 500 mL), and media volumes to further tease out the impact of differences in agitation-induced shear stress. However, efforts to isolate and magnify these mechanical differences revealed that shear stress cannot be separated from the broader physiochemical system. The results demonstrate that while massive differences in agitation drive a distinct hyperbranching response, the dominating influence of agitation-induced shear stress on morphological outcomes is reduced at lower speeds. As agitation becomes less overwhelming, inseparable environmental variables—coupled with the fungus’s own biological responses—predominate. Specifically, these lower-shear environments promoted the secretion of extracellular polysaccharides, driving hyphal aggregation and subsequent anastomosis (hyphal fusion). Ultimately, our findings show that morphological control cannot be reduced to stirring intensity alone; rather, it requires a systemic approach that accounts for both network expansion and network connection mechanisms.