Longitudinal Study of the Effects of Environmental pH on the Mechanical Properties of Aspergillus niger.

The regulation of environmental pH is key to the health of an ecosystem, influencing the metabolic activity, growth, and development of organisms within it. Although pH values can be measured by a wide range of readily available technologies ranging from fluorescent dyes and nanosensors, these cannot reveal the history of environmental pH from before monitoring begins. This information is sometimes crucial for piecing together what has happened to an ecosystem, and our long-term goal is therefore to develop technologies capable of obtaining it. Here, we propose monitoring environmental pH over time by tracking mechanical properties of a common fungus. As a first step toward obtaining a time history of pH, we evaluate the effect of pH upon the effective indentation modulus of spores and hyphae of Aspergillus niger. We report that the indentation modulus of this phosphorus-solubilizing fungus, obtained through atomic force microscopy and nanoindentation, correlated with environmental acidity. We observed a significant, monotonic increase in moduli over the course of incubation in an acidic environment, but no change in moduli over time for incubation in a neutral environment. Results show promise for using our scheme to detect and track environmental pH over time, and more broadly for using a microorganism's mechanical properties as a biomarker for environmental detection.