Dove ROLAND THAXTER ’ S Legacy and the Origins of Multicellular Development Dale

R OLAND THAXTER published a bombshell in December, 1892. He reported that Chondromyces crocatus, before then considered an imperfect fungus because of its complex fruiting bodv, was actually a bacterium (Figure 1). THAXTER had discovered the unicellular vegetative stage of C. crocatus; the cells he found were relatively short and they divided by binary fission. C. crocatus was, he concluded, a “communal bacterium.” THAXTER described the locomotion, swarming, aggregation and process of fruiting body formation of C. crocatus and its relatives, which are collectively called myxobacteria, with an accuracy that has survived 100 years of scrutiny. He recognized the behavioral similarity to the myxomvcetes and the cellular slime molds, drawing attention in all three to the transition from single cells to an integrated multicellular state. He described the behavior of myxobacteria in fructification in terms of a “course of development” because it was “a definitely recurring aggregation of individuals capable of concerted action toward a definite end” (THAXI‘ER 1892). This essay will emphasize some implications of THAXTER’S demonstrations, often apparently unrecognized. The striking similarities to cellular slime mold development probably led JOHN TYLER BONNER and KENNETH B. RAPER, 50 years after THAXTER’S discovery, to take independent forays into myxobacterial development. RAPER, an eminent mycologist, had in fact discovered Dictyostelium discoidium, recognizing it as a superb subject for the study of morphogenesis, cellular differentiation and intercellular communication. BONNER was fascinated by morphogenesis and sought unifying principles behind the bewildering diversity (BONNER 1952, 1974). Both RAPER and BONNER seemed to be intrigued by the unusual example of morphogenetic movements exhibited by the myxobacteria as they formed fruiting bodies. RAPER saw “examples of interdependent cellular behavior that involve purposeful orientation, morphogenetic move-