XVI International Botanical Congess

Invasive hyphal growth depends upon mechanical penetration coupled with the action of substrate-degrading enzymes. We have used novel methods to investigate hyphal mechanics in the saprobic oomycete Achlya bisexualis, and human pathogen Pythium insidiosum. In Achlya, hyphal force (measured with silicon bridge transducers) shows strict temperature dependence, with a 48% reduction in force between 22 and 35 C. By contrast, hyphal force is undiminished at 37 C in the pathogenic Pythium, consistent with the behavior anticipated for a fungus that penetrates human tissue. Comparisons between these data and measurements of substrate strength using glass microprobes, prove that both fungi generate sufficient force to penetrate certain solid materials without using either exoenzymes to reduce substrate resistance or extracellular lubricants to accelerate extension growth.