SCANNING ELECTRON MICROSCOPY OF FRUITING BODY FORMATION BY STIGMATELLA AURANTICA AND CHONDROMYCES CROCATUS

Abstract

The study to be presented consists of two related parts. Scanning. electron microscopy was employed 1) to observe mature fruiting bodies of several myxobacter genera and 2) to study details of fruiting body formation by Stigmatella aurantica and Chondromyces crocatus. fiicrographs representative of both parts will be shown. Initially, technics for optimum fruiting body production.and for specimen preparation were perfected on the structually less complex fruiting bodies produced by species of Myxococcus and Cystobacter. These were then modified to permit an in depth study of fruiting body formation by pure cultures of S. aurantica and C. crocatus. In summary, vegetative cells of the latter two species were grown and then transferred to a nonnutrient medium for fructification. Fruiting‘body formation was interrupted at various stages by fixation with glutaraldehyde vapours. Fixed and dehydrated specimen were dried by the critical point method in liquid C0,. Fruiting in both species begins with an aggregation center which closely resembles a fried egg in appearance. It is after this stage that significant and consistant differences occur in fruiting between the two organisms., In S. aurantica, the "yolk region" of the fried egg stage extends upward to form a column-like stalk which is nearly uniform in diameter throughout its length. At maximum height the terminus of the stalk develops into an irregular pattern of bud-like swellings which eventually differentiate into sporangia. C. crocatus differs in chat the "yolk region" enlarges into a large bulbous structure initially. The bulb anpears to be lifted upward by a slender stalk which develops beneath. The bulb differentiates into numerous bud-like swellings at maximum stalk height, but unlike Stigmatella, the swellings and immature sporanoia are arranged in a distinctive radial pattern. This symmetry is lost as more sporangia develop and mature. Stalks of two week old mature fruiting bodies of both species appear cellular in composition. Stereomicrographs of cross sections of broken mature stalks suggest the cells are oriented parallel to the long axis of the stalk.