Koch described spores as egg-shaped structures, enclosed by a thin layer of protoplasm that he called bright matter. After 3-4 hours, he observed various stages of germination and outgrowth, which are depicted in Cohn's sketch. He fixed dried spores on a slide and incubated the sample with aqueous humor. (B) Koch followed spore germination and outgrowth, and determined that spores can form viable cells. The strings gradually decomposed, the spores were released and sank to the bottom of the droplet where they accumulated and could be kept for weeks. Koch depicted the structures in this sketch and likened them to fragile strings of pearls. After 10-15 h, these strings contained light refracting bodies, which he identified as spores. During the incubation, he observed the cells growing into string-like structures. He placed a slice of spleen containing the Bacillus into cow sera or aqueous humor, and incubated the specimens at 35-37☌ in an incubator that he himself had constructed. (A) Koch followed the sporulation process in B. In one of his most well-known studies, Robert Koch investigated the etiology of anthrax. 1.įIGURE 1: Early depictions of sporulation and germination in Bacillus spp. Their hand-drawn sketches of these processes are shown in Fig. anthracis, and realized that spores and vegetative cells are different cellular forms of the same bacterial species, and that cells can interconvert between these two forms, from vegetative cells to spores via sporulation, and from spores to vegetative cells via germination. Koch, in collaboration with Cohn, followed the sporulation-germination cycle in B. subtilis spores survive periods of boiling. Cohn initiated the study of the resistance properties of spores with the observation that B. It was not until nearly four decades later that endospores started to be characterized in seminal studies by Ferdinand Cohn and Robert Koch. The first reported observation of bacterial endospores dates back to 1838, when Christian Gottfried Ehrenberg noted refractile bodies inside bacterial cells. This review aims to discuss some of the key findings that have shaped the sporulation field, through the lens of bacterial genetics.Īrguably the most important milestone in endospore research was the actual discovery of endospores. The study of endospore formation, however, is full of fascinating discoveries that, while subtle enough to escape the attention of the mainstream media, have contributed to shape our current perception of bacterial cells. Furthermore, the use of Bacillus anthracis (anthrax) spores in biological warfare and, more recently, in bioterrorist attacks has brought the bacterial spore to the attention of modern society. In fact, it has been claimed that viable endospores were isolated from the gut of extinct bees buried in Dominican amber more than 25 million years ago, evoking the imagery of Jurassic Park. Bacterial endospores are among the most resilient cell-types known, and can survive for very long periods of time without any nutrients. This should not come as a surprise, as some properties of endospores could well be in the headlines of the popular press. spores) have attracted the attention of the scientific community and, at times, even the general public. Since their discovery, bacterial endospores (a.k.a.
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