Microfluidic monitoring of the growth of individual hyphae in confined environments

Soil fungi have the ability to form large mycelial networks. They rely on
the resources available in the soil to produce biomass, and are able to
degrade complex biomolecules. Some of them can even degrade recalcitrant
organic pollutants and are considered promising candidates for soil
bioremediation strategies. However, the success of this approach depends
on the ability of fungi to colonize the soil matrix, where they encounter
spatial and temporal variations of confinement, humidity and nutrient
concentration. In this paper, we present a study of fungal growth at the
scale of single hyphae in a microfluidic device, allowing fine control of
nutrient and water supply. Time-lapse microscopy allowed simultaneous
monitoring of the growth of dozens of hyphae of Talaromyces helicus, a
soil isolate, and of the model fungus Neurospora crassa through parallel
microchannels. The distributions of growth velocity obtained for each
strain were compared to measurements obtained in macroscopic solid
culture. For the two strains used in the study, confinement caused the
growth velocity to drop in comparison with unconfined experiments. In
addition, N. crassa was also limited in its growth by the nutrient supply,
while the microfluidic culture conditions seemed better suited for T.
helicus. Qualitative observations of fungi growing in microfluidic
chambers without lateral confinement also revealed that side walls
influence the branching behavior of hyphae. This study is one of the first
to consider the confinement degree within soil microporosities as a key
factor of fungal growth, and to adress its effect, along with
physicochemical parameters, on soil colonization, notably for
bioremediation purposes.