ORDER VIII. MYXOBACTERALES JAHN, 1915. 



(Myxobacteriaceae (sic) Thaxter, Bot. Gaz., 17, 1892, 394; Myxobactrales Clements, The 

 genera of fungi. Minneapolis, 1909, 8; Jahn, Kryptogamenflora der Mark 

 Brandenburg, V, Heft 1, 1915, 187.)" 



Myx.o.bac.te.ra'les. M.L. mas.n. Myxobacter name of the genus first described by Thax- 

 ter; -ales ending to denote an order; M.L. fern. pi. n. Myxobacterales the order based upon 

 the type genus, Myxobacter. 



Common or trivial name. The myxobacters. 



Brief characterization of the order. The vegetative cells are flexible rods of low re- 

 fractility which exhibit gliding movement on solid surfaces and which multiply by binary, 

 transverse fission to produce a thin, flat, rapidly extending colony. Actively motile cells 

 at the periphery of the colony commonly occur as groups of 2 or 3 to several hundred indi- 

 viduals in the form of tongue-like extensions or isolated islands whose presence is virtually 

 diagnostic of the order. The moving cells may pave the substrate with a thin layer of slime 

 on which they rest. 



Resting cells are formed by all myxobacters except members of the genus Cyiophaga. In 

 the family Myxococcaceae the resting cell is a spherical or oval body, thick-walled and highly 

 refractile; in the remaining groups it is merely a shortened vegetative cell. Except in the 

 genus Sporocytophaga, resting cells are borne in or on spatially localized, larger structures 

 known as fruiting bodies. In the simplest case, the fruiting body consists of a uniform mass 

 of resting cells held together by slime. Some groups produce more complex fruitingstructures : 

 the resting cells may be enclosed in cysts and may be raised above the substrate on stalks, 

 either simple or branched. Fruiting bodies are usually brightly colored and often sufficiently 

 large to be visible to the naked eye. 



The vegetative state. In the vegetative condition, m3'xobacters consist of unicellular 

 rods which occur in two characteristic shapes. Members of the iamily Sorangiaceae, together 

 with some representatives of the families Archangiaceae and Polyangiaceae, have cylindrical 

 vegetative cells with blunt, rounded ends; in extreme cases the cell is broader at the tips 

 than at the center. All other myxobacters, with the possible exception of some Cytophaga 

 species, have vegetative cells which taper towards the tips. The cells are not surrounded 

 by a demonstrable wall and, perhaps as a consequence, are flexible and very weakly re- 

 fractile. Division is always by binary, transverse fission. Motility is universal. Movement 

 occurs only in contact with a solid surface and is of the gliding type also found in the Cyano- 

 phyta and in filamentous, colorless organisms such as the Beggiatoaceae and Vitreoscillaceae. 

 There are no demonstrable means of locomotion, and the actual physical mechanism of 

 movement is not understood, although many authors have offered speculations, which were 

 recently reviewed by Meyer-Pietschmann (Arch. Mikrobiol., 16, 1951, 163). Discrete nuclear 

 structures similar to those of true bacteria can be demonstrated by appropriate cytological 

 procedures. Their appearance and behavior during division and formation of resting cells 

 are described and illustrated by Badian (Acta Soc. Bot. Poloniae, 7, 1930, 55), Krzemieniew- 



*Revised by Professor R. Y. Stanier, Department of Bacteriology, University of Cali- 

 fornia, Berkeley, California, March, 1953. 



854 



