Temperature/Growth Relationships of a Thermophilic Actinomycete, Micromonospora vulgaris

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The thermophilic actinomycete Micrornonospora vulgaris resembles known mesophilic members of the genus Micromonospora in reproducing by means of small refractile spores borne singly on lateral branches of the vegetative mycelium.Its distinctive feature is the consistent production of a secondary aerial mycelium under optimal laboratory cultural conditions and in grass composts during the high temperature phase. This aerial mycelium is composed of abundantly branched, hydrophobic filaments which rapidly segment. The cells in these filaments may in turn give rise to similar refractile spherical spores borne singly on very short lateral branches. The reproductive pattern here described is one of the most complex yet known among the actinomycetes. It is thought that the aerial phase of development is intimately associated with the thermophilic nature of the organism.When originally defining the genus Micromonospora, Orskov (1923) described the type-species, M . chalceae, as completely devoid of aerial mycelium, reproduction taking place by means of small spherical to oval spores borne singly on the distal ends of short lateral branches of the vegetative mycelium. are all of the nocardial type, a sparse development of mostly unbranched and undivided filaments. Such development is spasmodic and infrequent and does not represent a sporogenous phase.' This view was in accordance with the work of Waksman, Umbreit & Cordon (1939) on the thermophilic actinomycetes which occur in dunged composts and soils. Thus, although they noted that their strains of M . vulgaris differed from the mesophilic strains described by Jensen (1930) by the appearance of a slight aerial mycelium on certain media, they considered this of no significance and stated that 'the aerial mycelium, though present, is usually rudimentary, rarely exhibiting the tangled network of strands typical of Actinomyces species '. The observation of Miehe (1907) and other early workers that the white lime-like coating on hot compost heaps was caused by thermophilic actinomycetes was re-emphasized by Forsyth & Webley (1948). Erikson (1952) explained this appearance as due to the very abundant production of an aerial mycelium which was hydrophobic and gave rise to heat-resistant spores. The brief description of the development of M. vuZgaris which follows is based on the almost continuous observation, during a period of two to three years, of seven strains, six, M, D, F, D,, B,, B,, isolated from composts, and a seventh, H, isolated from canned ham by Dr Heller. METHODSDuring experiments detailed elsewhere (Erikson, 1952) spore suspensions of suitable concentrations were continually being prepared. These were streaked on blocks of agar for slide cultures, or on strips of cellophan laid over the

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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The Reproductive Pattern of Micromonospora vulgaris

Erikson

1953

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“…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.…”

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confidence: 69%

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

Erikson

1954

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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.

“…This gives rise to the question : does the physiology of the aerial mycelium vary from that of the vegetative growth? That the aerial growth of' Micromonospwa vulgaris is likely to be physiologically different from the vegetative growth is supported by the differences in morphology and the presence of lipid staining material in the former, which is absent from the latter (Erikson, 1952).…”

Section: Discussionmentioning

confidence: 99%

The Effect of Oxygen on the Growth and Metabolism of the Aerobic Thermophilic Actinomycete Micromonospora vulgaris

Webley¹

1954

SUMMARY: In the presence of pure oxygen at one atmosphere pressure Micromonospora vulgaris is unable to form in liquid media a surface pellicle of growth-bearing aerial mycelium. The production of bottom growth is either unaffected or stimulated by oxygen. Vegetative mycelium which develops from spores in Warburg vessels has an oxygen uptake that is similar in the presence of air or oxygen. Aerial mycelium, harvested from growths in air, shows marked differences as regards oxygen uptake in the presence of air or oxygen; oxygen is inhibitory. Some evidence is presented to show that the effect of oxygen may be connected with the inactivation of essential -SH groups of thiol enzymes.Full and detailed accounts of the isolation, cultivation, temperature/growth relationships and reproduction of the thermophilic actinomycete Micromonospora vulgaris were given by Erikson (1952, 1953a, b). She showed that this organism possesses the most complex reproductive pattern of any actinomycete yet studied, and considers that 'the device of producing a secondary aerial mycelium capable both of further growth and of producing spores, more than doubles the expected life of a mycelial organism a t elevated temperatures'. Erikson & Webley (1953), in a study of the respiration of the different growth phases of this structurally complex organism, found that a high rate of oxygen uptake a t 60" was associated with the presence of aerial mycelium harvested from 1-to %day cultures grown on liquid medium a t 60°, while bottom growth harvested under similar conditions was inactive in this respect. It has now been possible to show that pure oxygen exerts an inhibitory effect on the production of aerial mycelium (in growth experiments) and metabolism of aerial mycelium (respiration experiments; Webley, 1953) of this aerobic organism. The production of vegetative growth is unaffected by these differences in the gas phase. METHODS Organism.The experiments presented here were performed with strain H of Micromonospora vulgaris (Erikson, 1953 a).Technique of growth. Material from 2-day-old growth on liquid CPS medium was used throughout (see Erikson & Webley, 1953).Preparation of spore suspensions and aerial mycelium for the Warburg experiments. Spore suspensions were obtained by shaking the pellicle of growth finally obtained, after washing free of medium, in 5 ml. of ~/ 7 5 phosphate buffer (pH 7.0) on a 'Microid' shaker for 5 min. This process resulted in the detachment of a high proportion of the spores which could be separated from