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Abstract
Colony expansion is an essential feature of fungal infections. Although mechanisms that regulate hyphal forces on the substrate during expansion have been reported previously, there is a critical need of a methodology that can compute the pressure profiles exerted by fungi on substrates during expansion; this will facilitate the validation of therapeutic efficacy of novel antifungals. Here, we introduce an analytical decoding method based on Biot’s incremental stress model, which was used to map the pressure distribution from an expanding mycelium of a popular plant pathogen, Aspergillus parasiticus. Using our recently developed Quantitative acoustic contrast tomography (Q-ACT) we detected that the mycelial growth on the solid agar created multiple surface and subsurface wrinkles with varying wavelengths across the depth of substrate that were computable with acousto-ultrasonic waves between 50 MHz–175 MHz. We derive here the fundamental correlation between these wrinkle wavelengths and the pressure distribution on the colony subsurface. Using our correlation we show that A. parasiticus can exert pressure as high as 300 KPa on the surface of a standard agar growth medium. The study provides a novel mathematical foundation for quantifying fungal pressures on substrate during hyphal invasions under normal and pathophysiological growth conditions.
Highlights
To address the critical need for quantitative tools for measuring fungal invasion, we have recently developed a methodology for 3D tomography of a growing fungal colony[14]
As a first step to establish the mathematical foundation for subsurface pressure profiling, we performed Quantitative Acosutic Contrast Tomography (Q-ACT) imaging on A. parasiticus colonies grown on a nutrient rich growth medium
To compute the pressure that resulted in the wrinkles in the substrate, we proceeded to understand the relation between the pressure profiles from the colony and the wrinkle patterns created in the substrate
Summary
Imaging of the wrinkles in the growth substrate with QACT. As a first step to establish the mathematical foundation for subsurface pressure profiling, we performed Q-ACT imaging on A. parasiticus colonies grown on a nutrient rich growth medium (yeast extract sucrose agar, YES agar). To avoid such singularity problem, Biot’s incremental stress theory was proposed[19]. Further pressure applied on the agar media acted as the initial stress, and was further incremented. To determine the pressure from the A. parasiticus colony that created the observed wrinkles, we incorporated in our calculations the following values: depth of the agar media, H = 2.14 ± 0.08 mm, Elastic Modulus, E, of the Agar media = 700 ± 2 1 kPa, that was determined from the wave velocity in the medium[14,31], and Poisson ratio, 0.49. We report our model as a more generalized incremental stress model with boundary effect
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