FAMILY MYCOBACTERIACEAE 875 



ORDER II. ACTINOMYCETALES BUCHANAN. 



(Jour. Bact., 2, 1917, 162.) 

 Organisms forming elongated cells which have a definite tendency to branch. These 

 hyphae do not exceed 1.5 microns and are mostly about 1 micron or less in diameter. 

 In the Mycobacteriaceae the mj'celium is rudimentary or absent ; no spores are formed ; 

 the cells are acid-fast. The Aciinomycetaceae and Strepiomycelaceae usually produce 

 a characteristic branching mycelium and multiply by means of special spores, oidio- 

 .spores or conidia. Special spores are formed by fragmentation of the plasma within 

 straight or spiral-shaped spore-bearing hj'phae; the oidiospores are formed by seg- 

 mentation, or hy transverse division of hyphae, similar to the formation of oidia 

 among the true fungi ; the conidia are produced singly, at the end of simple or branch- 

 ing conidiophores. They grow readily on artificial media and form well-developed 

 colonies. The surface of the colony, especially in the Aciinomycetaceae and Strepto- 

 mijcetaceae , may become covered with an aerial mycelium. Some form colorless or 

 white colonies, whereas others form a variety of pigments. Some species are par- 

 tially acid-fast. In relation to temperature, most are mesophilic, while some are 

 thermophilic. Certain forms are capable of growing at low oxj'gen tension. The 

 Order as a whole is composed of saprophj'tic species, but also includes species that 

 are parasitic and sometimes pathogenic on both animals and plants. 



Key to the families of order Actinomycetales. 

 I. Mycelium rudimentary or absent, no spores formed. Acid-fast. 



Family I. Mycobacteriaceae, p S75. 



II. True mycelium produced. 



A. Vegetative mycelium divides by segmentation into bacillary or coccoid 



elements. Some species partially acid-fast. 



Family II. Actinomycetaceae, p. 892. 



B. Vegetative mj'celium normally remains undivided. 



Family III. Streptomycetaceae, p. 929. 

 Among the recent sj'stems of classification of this order it is sufficient to mention 

 the following: Baldacci (INR-copath., 2, 1939, 84) divided the order Actinomycetales 

 into two families: (a) Mycobacteriaceae Chester with two subfamilies, Leptotrichi- 

 oideae Baldacci and Proactiiiomycoideae Baldacci, each with five genera, and (b) 

 Actinomycetaceae Buchanan, with two genera, Micromonospora and Actinomyces. 

 Krassiluikov (Ray fungi and related organisms, Izd. Akad. Nauk, Moskow, 1938) 

 divided the order into (a) Actinomycetaceae, with four genera, Actinomyces, Proac- 

 tinomyces, Mycobacterium and Mycococcus, and (b) Mtcromonosporaceae, with one 

 genus, Micromonospora. Waksman (Jour. Bact., 39, 1940, 549) divided the order into 

 four families: Mycobacteriaceae, Proactinomycetaceae, Actinomycetaceae and Mtcro- 

 monosporaceae. 



FMIILY I. >IYCOBACTERIACEAE CHESTER.* 

 (Chester, Man. Determ. Bact., 1901, 349; Proactinomycetaceae Lehmann and Haag, 

 in Lehmann and Neumann, Bakt. Diag., 7 Aufl., 2, 1927, 674.) 



* Completeh' revised by Prof. G. B. Reed, Queens University, Kingston, Ontario, 

 Canada, December, 1938; minor revisions, December, 1944; with a complete revision 

 of Mycobacterium, leprae and ]\l. Icpracmurium by Dr. John H. Hanks, Leonard Wood 

 Memorial, American Leprosy Foundation, New York, N. Y. 



