Spontaneous rotational inversion in Phycomyces.

The filamentary fungus Phycomyces blakesleeanus undergoes a series of remarkable transitions during aerial growth. During what is known as the stage IV growth phase, the fungus extends while rotating in a counterclockwise manner when viewed from above (stage IVa) and then, while continuing to grow, spontaneously reverses to a clockwise rotation (stage IVb). This phase lasts for 24-48 h and is sometimes followed by yet another reversal (stage IVc) before the overall growth ends.

Estimates of biomechanical forces in Magnaporthe grisea.

The mechanical actions of the fungus Magnaporthe grisea raise many intriguing questions concerning the forces involved. These include: (1) the material properties of the appressorial wall; (2) the strength of the adhesive that keeps the appressorium anchored to the rice leaf surface; and (3) the forces involved in the penetration process whereby a peg is driven through the host cell wall. In this paper we give order of magnitude estimates for all three of these quantities.

Biomechanical model for appressorial design in Magnaporthe grisea.

The fungus Magnaporthe grisea, commonly referred to as the rice blast fungus, is responsible for destroying from 10% to 30% of the world's rice crop each year. The fungus attaches to the rice leaf and forms a dome-shaped structure, the appressorium, in which enormous pressures are generated that are used to blast a penetration peg through the rice cell walls and infect the plant. We develop a model of the appressorial design in terms of a bioelastic shell that can explain the shape of the appressorium, and its ability to maintain that shape under the enormous increases in turgor pressure that can occur during the penetration phase.

Growth induced curve dynamics for filamentary micro-organisms.

The growth of filamentary micro-organisms is described in terms of the geometry of evolving planar curves in which the dynamics is determined by an underlying growth process. Steadily propagating tip shapes in two and three dimensions are found that are consistent with experimentally observed growth sequences.

Biomechanical models of hyphal growth in actinomycetes.

The tip growth of filamentary actinomycetes is investigated within the framework of large deformation membrane theory in which the cell wall is represented as a growing elastic membrane with geometry-dependent elastic properties. The model exhibits realistic hyphal shapes and indicates a self-similar tip growth mechanism consistent with that observed in experiments. It also demonstrates a simple mechanism for hyphal swelling and beading that is observed in the presence of a lysing agent.

Self-similar tip growth in filamentary organisms.

The growth of a family of filamentary microorganisms is described in terms of self-similar growth at the tip which is driven by pressure and sustained by a wall-building growth process. The cell wall is modeled biomechanically as a stretchable elastic membrane using large-deformation elasticity theory. Incorporation of geometry dependent elastic moduli and a self-similar ansatz shows how these equations can generate realistic tip shapes corresponding to a self-similar expansion process.