Morphological Studies in the Genus Nocardia IV. Bright Phase Contrast Observations of Living Cells

Abstract

A complete life cycle study of Nocardia species has not yet been made. One reason for this is that these organisms are difficult to study cytologically because of their small size. Hyphae of actinomycetes are around 1 micron in diameter, although mycelial development may be quite extensive. problem of variation in actinomycetes (Streptom yces species especially) has received a great deal of attention. So far no one has been able to explain the exact nature of this variation or to study it from a genetical point of view because of the lack of a complete life cycle cytological study. importance of such studies was recently emphasized by Jones (1954) who said, The organism must be better understood before we can make any headway in comprehending variability in Streptomyces. First and foremost an intensive cytological study is needed to give whatever direct information modern techniques can reveal on the finer structure of filaments and spores. Researches on developmental morphology will be of almost equal importance as the whole question of a two-phase life cycle must be settled one way or another. If definite nuclei exist, it may be possible to explore their genetical constitution by the production of heterocaryons through hyphal anastomoses. problem of variation in Nocardia species, closely related to Streptomyces species, has not received much attention due to the relative unimportance of the former to man. Life cycle and cytological studies have similarly been neglected. author (1950) studied the cytology of Nocardia species by means of lightand electron-microscopy and microchemical tests and discovered the presence of two different particulate structures in the cytoplasm, but was unable to demonstrate their exact nature. In hyphae grown on medium without nitrogen, internal structure became very clear in electron microscopic studies (figs. 63 and 64). Two kinds of particulate structures were present of different natures which alternated in filaments. A positive Feulgen reaction, generally considered to be the sine qua non for proof of nuclei was not demonstrated. presence of fat, and carbohydrate-like bodies in the cytoplasm was shown, and no particles possessed the solubilities of volutin. Although the presence of nuclei was not proved in these experiments, strong cytological evidence was presented for their occurrence. Morris (1951) studied the cytology