The Reproductive Pattern of Micromonospora vulgaris

Abstract

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

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

“…3 and 'nids', P h a u et al 1954). Such structures developed away from the glass as the growing filaments shifted direction slightly in accordance with the varying food supply, A photograph of such a ' loop ' produced under identical conditions to those described has already been published for Micromonospora vulgaris (Erikson, 1953: pl. 1, fig.…”

DNA-DNA relatedness among Thermoactinomyces species: Thermoactinomyces candidus as a synonym of Thermoactinomyces vulgaris and Thermoactinomyces thalpophilus as a synonym of Thermoactinomyces sacchari.

“…For example, the ability to utilize starch, which was previously not observed, is found in the description of Thermoactinomyces vulgaris of the 8th edition of the Manual (Ku$ ster, 1974). Kurup et al (1975) classified the isolates lacking amylase as Thermoactinomyces candidus and the isolates producing amylase as Thermo- Erikson (1953) as Micromonospora vulgaris strain D, which is listed as strain KCC A-0162 in the Approved Lists of Bacterial Names (Skerman et al, 1980). This strain corresponded to the original concept of Thermoactinomyces vulgaris by Tsiklinsky (1899) and the concept of Thermoactinomyces candidus.…”

A Defined Medium for the Growth of the Thermophilic Actinomycete Micromonospora vulgaris

“…The flasks were set up in duplicate and examined daily for surface and bottom growth. Owing to the complex morphology of Micromonospora vulgaris (Erikson, 1953) it was not found possible to record the results of the growth experiments by conventional methods. Also, because of the inherent variability of a thermophil of such complexity of structure, it was found that not all the flasks gave uniform growth.…”

“…In this way little evaporation took place from the shallow liquid layer during the incubation period of 8-10 days at 58-60'. To ensure a water-saturated environment for maximum production of aerial growth (see Erikson, 1953) the side arms of the filter flasks were closed by means of short pieces of pressure tubing clipped with screw clamps. No evidence of limitation of growth by lack of oxygen was observed under these conditions.…”