54 
PACIFIC SCIENCE, Vol. XXII, January 1968 
MATERIALS AND METHODS 
Cultures were grown in broth on a Gyrotary 
shaker (New Brunswick Scientific Co.) at 200 
rpm for three to four days. Sodium caseinate 
broth (Fred and Waksman, 1928) as modified 
by L. F. Potter (bbl No. 01-549) was the me- 
dium of choice. Fixation and embedding were 
performed according to the standard procedures 
of Kellenberger and Ryter (1958). Sections 
were cut on a Porter-Blum ultramicrotome and 
poststained with lead citrate. Electron micro- 
graphs were obtained on a Norelco EM 75 
microscope. 
micromonosporae. The interpretation of the 
branched cells is less clear. This might be inter- 
preted as true branching or as the result of 
anastomosis of two hyphae. Leudemann and 
Brodsky (1965) reported sectoring in colonies 
of M. carbonacea which represented sporulating 
and non-sporulating areas. They compared this 
to the well-known heterocaryotic behavior in 
fungi. Both anastomosis and sectoring are sug- 
gestive evidence which calls for confirmation 
in the entire group of micromonosporae. 
SUMMARY 
RESULTS 
The preliminary findings reported here dem- 
onstrate that the technique employed offers 
promise for its use in future investigations. 
All pictures taken clearly show the procaryotic 
nature of the three Mzcromonospora species: 
the nuclear areas are fibrillar and not surrounded 
by a membrane; the cytoplasm is densely gran- 
ular and essentially devoid of lamellar organ- 
elles. 
The hyphae of all three species sectioned 
(Figs. 1, 6, 7) show cross-walls or septa. These 
are particularly numerous in M. purpurea (Figs. 
3, 4, 5, 7). Apparently there are no septal pores. 
Some branching was observed (Figs. 3, 4, 7). 
Spore formation seems to be initiated by the 
development of a heavy septum or plug within 
the hypha which isolates the apical end of the 
hypha as a roundish, somewhat enlarged struc- 
ture filled with both cytoplasmic and nuclear 
material (Figs. 1, 4). The final spore (Fig. 2) 
has a sculptured wall. Wall sculpturing was 
shown by Leudemann and Brodsky (1964) on 
the spores of M. echinospora, but their pictures 
are completely devoid of inner detail. 
DISCUSSION 
Despite the preliminary nature of this report 
several points are worth emphasizing. The pro- 
caryotic nature of the cells has been established 
definitely for all three Mzcromonospora studied. 
Septa, which are particularly abundant in M. 
purpurea , are demonstrated clearly in all the 
strains considered: there should be no question 
of the occurrence of cross-walls in these three 
Electron microscope studies of three species 
of the genus Mzcromonospora were made to 
clarify the scanty and conflicting information 
about cellular structure in this group. All ma- 
terials revealed clearly the procaryotic nature 
of the cells and the presence of definite cross- 
walls in the hyphae. 
REFERENCES 
Agre, N. S. 1962. Electron-microscopic inves- 
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Arai, T., Y. Koyama, S. Kuroda, and H. 
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Avery, R. J., and F. Blank. 1951. On the 
chemical composition of the cell walls of the 
Actinomycetales and its relation to their 
systematic position. Canadian J. Microbiol. 
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Castellani, A., M. M. X. De Brito, and 
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Fred, E. B., and S. A. Waksman. 1928. Lab- 
