MICRO-ORGANISMS 17 



plore some of the possibilities of more widespread utilization of the 

 fungi and their products. Aspergillus and Penieillium seem to be 

 especially versatile genera, yielding important organic acids, antibio- 

 tics, and enzymes. However, other imperfect genera are also gaining 

 recognition, especially in the microbiological conversion of steroids. 

 Members of the genera Fusarium, Cladosporium^ Trichoderma, Hen- 

 dersonia, Trichothecium, Curvularia, Botrytis, and Nigrospora have 

 been found to accomplish desirable transformations of the steroid 

 molecule by hydroxylation, epoxidation, or dehydrogenation. This 

 tailoring of molecules by micro-organisms seems to be not only a trend 

 that will continue but one that will expand considerably in the future. 



Myxomycetes 



The class Myxomycetes comprises a small closely related group of 

 primitive organisms, which have been placed in both the animal and 

 plant kingdoms, but which apparently are more closely related to the 

 true fungi. They are of little economic importance, if any, and ac- 

 cording to Ainsworth (1) number only about 400 species. They have 

 been called Myxothallophyta, Mycetozoa. Myxogastres, Phytosarco- 

 dina, or slime molds by various authors referring to them either singly 

 or in association with other groups of uncertain affinities. 



The Myxomycetes are widely distributed, free-living forms, which 

 are found in damp or wet places, such as on old logs or other decom- 

 posing plant material. They resemble the true fungi in their lack of 

 photosynthetic pigments and in their food reserves. They differ from 

 them in their growth or assimilative phase, which consists of a single 

 large protoplast called a plasmodium. It is multinucleate, motile, 

 and naked. 



The life cycle is rather unusual. A germinating spore produces one 

 to four ameba-like, flagellated, swarm cells, which may function im- 

 mediately as gametes by uniting in pairs or which may, by loss of their 

 flagella, become "myxamebae" and undergo divisions before copula- 

 tion. The resultant zygote is ameboid and grows directly into a Plas- 

 modium living in or moving slowly on a substratum. The plasmodium 

 ingests micro-organisms, spores, or bits of dead plant and animal mate- 

 rial and increases in size, generally to several centimeters in diameter. 

 Nuclear fusion may occur at zygote formation or later. After severa 1 

 nuclear divisions and sufficient growth, the plasmodium humps up and 

 becomes converted into one or more sessile or stalked sporangia or 

 spore cases. Meiosis occurs before spore formation, which then com- 

 pletes the life cycle. 



The chief characters for the classification of the Myxomycetes are 

 the method of spore development ; the type of fruit body ; the structure 

 of the spore case and the threadlike material, or capillitium, inside ; the 

 calcium carbonate, where present; and the size, color, and ornamenta- 

 tion of the spores (1). Although the Acrasiales, which includes the 

 genus Dictyostelium* and the Labyrinthulales, with Lahyrinthida, 

 have sometimes been classified along with the Myxomycetes, their 

 affinities are highly uncertain, and the class Myxomycetes is generally 

 restricted to the slime molds that have a true plasmodium. A good 



