Oriented Movement of Blue-Green Algæ on a Stretched Gel

Abstract

TROPISTIC and tactic responses to stresses in an elastic substrate have been described for several kinds of biological material. The true bacterium Kurthia zopfii, when grown in gelatin subjected to mechanical tension, reflects precisely in its pattern of growth the pattern of stresses in the substrate^1–3 ; a similar response is shown by nerve fibres cultivated on stretched coagulated plasma⁴. Jacobsen¹ proposed the name 'elasticotropism' for this type of behaviour. A few years ago, the corresponding tactic response was demonstrated in myxobacteria on stretched agar gels⁵. The effect of elasticotaxis in these organisms is particularly striking through its secondary influence on the fruiting process ; the rigidly oriented movement of the vegetative cells causes marked abnormalities in the shape and distributional pattern of the fruiting bodies.