A Note on Elasticotaxis in Myxobacteria

Abstract

When myxobacteria of the family Myxococcaceae are grown on agar slants, a striking abnormality in the production of fruiting bodies is often apparent. The fruits formed along the line of inoculation are not scattered at random, but are definitely oriented in roughly parallel lines at right angles to the line of inoculation. Sometimes each line is composed of a series of the usual discrete, approximately spherical fruiting bodies, but in other cases the individual fruits become confluent, so that a ridge of microcysts is formed. Due to the spread of the vegetative swarm, fruits are also ultimately formed on the agar surfaces on either side of the line of inoculation; such fruits always exhibit the customary random distribution and normal shape. In fig. 1 is shown a slant culture of Myxococcus fulvus which illustrates this phenomenon. It was first observed in this species, but is also exhibited by all the other members of the Myxococcaceae which I have studied. In seeking for an explanation of this behavior, it was at once apparent that chemical stimuli could not be invoked, since they would also have affected the fruiting process as it occurred in the regions of the slant surface away from the line of inoculation. The only conceivable difference between the streaked and unstreaked areas of the agar was a physical one. Accordingly, a series of experiments was performed in order to clarify the nature of the physical forces involved. MATERIALS AND METhODS As a test organism, Chondrococcus (Myxococcus) exiguus (Kofler) nov. comb.2 was selected since it possessed several marked advantages for the purposes of the investigation. The fruiting bodies of this species are very small and inconspicuous , but they are formed in extreme abundance and in a comparatively short period of time on dung agar. The medium employed throughout was dung-decoction agar. The dung decoction was prepared by boiling horse or rabbit dung with twice the volume of water for 15 or 20 minutes, filtering, and diluting to an appropriate concentration (usually a tenfold dilution; this has to be varied somewhat, however, from one lot of dung to the next). To the diluted dung decoction 2% agar was added.