The Morphology, Cytology, and Taxonomy of the Actinomycetes

1955

SUMMARY : Several isolates of monosporous lines of Streptomyces coelicolor, both normally pigmented and colourless variants, were obtained by microdissection of young vegetative mycelia. In each case their properties largely resembled those of the parents. This material was studied together with three strains of Streptomyces scabies of varying degrees of virulence, which had been isolated from potato scab lesions. Modifications of growth were noted with respect to gross colonial morphology on agars containing detergents, structure of aerial mycelium arising from various types of surfaces, and development of germinating spores in liquids and in contact with non-nutritive plane surfaces. In both species-groups those organisms which produced least aerial mycelium on stock nutrient agar were most susceptible to the inhibitory influence of 0-01 yo Gemex 29 on the development of aerial mycelium in simpler media. Distorted aerial growths on detergent agar resembled irregular swollen sporogenous filaments produced in pectin + ammonium salt liquid media.These were also reminiscent of cases of sporogenesis in submerged cultures described by other workers. Apart from surface tensions operating at the air/medium interface, the relative degree of humidity in the culture vessel was found to have some effect upon variation of spore size. Germinating spores and young filaments growing in contact with plane surfaces were more prone to elongation than those growing in liquids. Branching was also influenced to a considerable extent by the nature of the physical environment.In a recent review Hendlin (1954) pointed out that inadequate attention has in the past been paid to the profound effect which the physical environment must have upon the nutrition of micro-organisms. Such a viewpoint, which was restricted by Hendlin mainly to a consideration of such physical factors as temperature, pH values, oxidation-reduction potential, and CO, tensions in so far as they cause perceptible nutritional differences, can almost certainly be extended to other aspects of microbiology. Thus the alteration of the energy relationships at interfaces which is brought about by the addition of surfaceactive agents to the media in which various acid-fast bacteria are grown is a recognized method of altering the character of the growth of the organisms (Alexander & Soltys, 1946). Increased cell division and smaller cells result from the incorporation of Tween 80 in the media in which the non-acid-fast Nocardia turbata (Erikson, 1954) is cultivated. A certain degree of correlation has been noted between decreased humidity on the one hand, and increased production of sporogenous aerial mycelium by streptomycetes on the other (von Plotho, 1940;Erikson, 1947), suggesting that important phases in the development of a complex organism may be favoured or completely suppressed by fluctuations in the physical environment.

Section: Discussionsupporting

confidence: 66%

Loss of Aerial Mycelium and other Changes in Streptomycete Development due to Physical Variations of Cultural Conditions

1955

“…1). This mode of growth is comparable to that of mesophilic streptomycetes and fungi, but not to that of mesophilic micromonosporae (Erikson, 1949 and the inoculum to 85" for 10 min., rapidly sowing the flask, shaking it a t 33" for 30 min., and then immediately incubating at 60" gives a more or less coherent surface growth with abundant aerial mycelium in 18 hr. ; whereas unheated control flasks, sown with unheated inoculum from the same source, and shaken at room temperature, yield, as a rule, poor bottom vegetative growth only.…”

Section: Resultsmentioning

confidence: 63%

Temperature/Growth Relationships of a Thermophilic Actinomycete, Micromonospora vulgaris

1952

SUMMARY:The only thermophilic actinomycetes found in composts made from lawn cuttings were members of the genus Micromonospora. The isolates obtained agreed in the main with the description of M. vuZguris (Tsiklinsky) Waksman, Umbreit & Cordon. Three strains have been studied in detail. They are true thermophiles, with an optimum range of growth 45-60', and appear in abundance at the high-temperature phase of the compost, with a profuse production of aerial mycelium and spores. Spore gemination is induced by heat activation, 5 min. a t 85' securing growth under suboptimal conditions. Thin suspensions of spores in 1 yo sucrose or in very dilute nutrient broth withstand 100' for periods of up to 45 min. Only very dense aqueous or saline suspensions are tolerant of these exposures. Surface growth on cellophan bearing a high density of aerial mycelium and spores withstands dry heating a t 100' for 150 min. or a t 106' for 5 min.In an extensive study of 480 cultures of thermophilic and thermoduric microorganisms isolated from the dust, grain, hay, etc., as well as from the milk obtained on various dairy farms, Prickett (1928) found that the only true thermophiles were either spore-forming bacilli or actinomycetes. Gordon & Smith (1949), making a taxonomic survey of 216 presumed thermophiles collected from many sources, were able to reduce the sporing bacilli to two main species, Bacillus coagulans and B. stearothermophilus. The thermophilic actinomycetes have not yet been studied extensively, but from the accounts so far published it would seem that the forms occurring in grass composts belong predominantly to the genus Micromonospora. Tsiklinsky (1899) isolated an actinomyces-like thermophile from decaying straw, manure, etc. which she termed Thermoactinomyces vulgaris, and which was renamed Micromonospora vulgaris by Waksman, Umbreit & Cordon (1939) as the result of finding similar forms on contact slides in dunged composts. Schutze (1908) was the first to describe in detail the development of a thermophilic actinomycete occurring in spontaneously heated clover hay, which he named Actinomyces monosporus, and which from his pictures is clearly a species of Micromonospora. In their study of the decomposition of the protein and hemicellulose fractions in grass composts, Forsyth & Webley (1948) noted that the extensive chalk-white encrustation of the upper layers of the compost during the high-temperature phase was attributable to the growth of a species of Micromonospora.The present study deals with the thermophilic actinomycete flora obtained from a series of grass composts put up during two seasons in Webley's (1947) composting container, and in collaboration with Dr Webley. All isolates are micromonosporae, have marked features in common, and, apart from a broader temperature range and lack of growth on potato, agree in the main with the description of M . vulgaris.

“…To the advantages of clarity of observation and freedom from contaminating medium noted by many workers when a sheet of sterile cellophan is placed between medium and organism, there must be added, in the case of the actinomycetes, the further benefits that the growths in general tend to be flattened out with a greater proportion than usual of the cells developing in the same plane, while individual cells show a higher degree of elongation. These observations were first made by Lentze (1938) in connexion with the anaerobic actinomycetes, and have been repeatedly confirmed by the author for all groups of actinomycetes (Erikson, 1940(Erikson, , 1947(Erikson, , 1949(Erikson, , 1952.…”

mentioning

confidence: 62%

Factors Promoting Cell Division in a 'Soft' Mycelial Type of Nocardia: Nocardia turbata n.sp.

1954

SUMMARY : Various methods of preparing microcultures with liquids (hanging-drop) and solids (collodion, cellophan, agar) were compared with respect to the mode of growth of the test organism on a complex nutrient substrate. Cell division was promoted in general by lower temperatures, by ageing, by lack of humidity in solid cultures, by the action of surface tension operating in the more convex droplets, and by the addition of surface-active agents to liquid media. By varying the carbon sources in chemically defined media it was found that starch, glycogen, and to some extent glucose, favoured filamentation, i.e. retarded or inhibited cell division, in comparison with a considerable variety of other sugars. Of the nitrogenous sources, nitrate resulted in relatively poor growth mainly composed of mycelial aggregates that later exhibited cell division to the extreme limits ; ammonium salts yielded more profuse filamentous growth with less subdivision ; certain single amino acids induced a more uniform development of short rods ; while casein hydrolysate commonly produced a variety of cell elements showing subdivision in all stages. Single cell isolates were used throughout, and the mode of growth was studied by means of phase-contrast and electron microscopy.A cultural description of the test organism, Nocardia turbata, n.sp. is given a t the end of the paper.The indispensable criterion of the actinomycetes as a family is the formation of a branching mycelium. The outstanding character of the genus Nocardia is the fragmentation of this initial mycelium into short or long elements: branching, filamentous, bacillary or coccoid. The simplest way of subdividing this genus is in accordance with: (a) the rapidity or otherwise with which spontaneous fragmentation takes place ; ( b ) the degree, partial or complete, to which cell division is carried on with ensuing breaking-up of the mycelium. This is, in fact, the basis of the morphological classifications of Orskov (1923) and Jensen (1931), and of the derivative scheme proposed by Waksman & Henrici (1943) and adopted in the 6th edition of Bergey's Manual (1948).A 'soft' mycelial type of nocardia is, therefore, one in which cell division proceeds more or less rapidly and to the extreme limits. As a direct consequence of this fragmentation, such a strain exhibits in liquid cultures some degree of turbidity (as against the characteristic clarity shown by actinomycetes with structurally intact mycelium), while on solid substrates massive sowings result in smooth readily emulsifiable growth which entirely resembles that of many ordinary bacteria. The fragmented cells themselves often retain V-and Y-forms similar to those of corynebacteria. Indeed, it is because of the systematically interesting position-at the borderline between eubacteria and actinomycetes-that it is of value to study the ways in which cell division takes place within the transient chains and branching filaments of these short-lived mycelial aggregates.