Digital reconstruction and analysis of the growing and branching mycelial network of the model filamentous fungus Podospora anserina

From a single spore, fungi can colonize their environment through a very complex interconnected network of hyphae, the mycelium. Yet, the rules governing this growth are simple. Hyphae can only grow from the tip, branch (apically or laterally) creating a new hypha or fuse when meeting another one. However, the local dynamics of growth within the network is not well known such as the interactions between hyphae. Both types of branching are difficult to analyse spatially and quantitatively, as is the long-distance tracking of apexes. In this work, we characterize the hyphal network expansion and the structure of the model filamentous fungus Podospora anserina under controlled culture conditions. To this end, temporal series of pictures of the network dynamics are produced, starting from germinating ascospores and ending when the network reaches thousands of connections approximately 20 hours later. The completely automated image reconstruction steps allow a post-processing and a quantitative analysis of the spatio-temporal dynamics using gray level information from the entire image series. Taking advantage of the network's properties we can numerically identify each individual hypha and characterise the nature of the branching it emerges from. Building on spatio-temporal information, we can discriminate hyphal fusion from mere overlapping to get a better understanding of the network topology. Thanks to the identification of each hypha, we analyse the growth of the network at both local and global scale.