Differentiation of the Vegetative and Sporogenous Phases of the Actinomycetes: 2. Factors affecting the Development of the Aerial Mycelium

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SUMMARY : Variation in the Actinomyces coelicolor species-group comprises loss of pigment and aerial mycelium, and occasionally of agar liquefaction. Stable variants may arise from degenerate, aged, vegetative mycelium, but do not normally do so when the vegetative mycelium is kept in vigorous condition by frequent subcultivation in suitable media. Single spore isolations from the aerial mycelium of typical and of variant colonies show that there may be inherent differences in the sisterspores of the same chain. Thus, in an agar-liquefying strain 3 of 15 spores had lost the power to produce pigment and to liquefy agar; and an atypical colony of the same strain yielded three viable isolates each with a strong tendency towards sectoring, with the ultimate production of a colourless, non-agar-liquefying variant as well as the typical growth. A non-agar-liquefying strain, which by prolonged cultivation in the vegetative phase had lost its power of producing the red-blue indicator pigment, yielded a variant giving rise to sectored colonies with occasional restoration of the blue pigment. Spontaneous occurrence of variants may be detected in certain spores of the aerial mycelium of a well-grown typical colony, although it is more readily seen in the spores of degenerate colonies which have been rendered atypical by artificial methods of cultivation.Much of the confusion existing in the literature concerning the extreme variability of the actinomycetes is due to lack of recognition, or forgetfulness, of their peculiar habits of growth. The ordinary actinomycete colony (Cohnistreptothriz Group I Orskov, Streptomyces Waksman) is not a colony in the bacterial sense; i.e. it is not an assemblage of disparate cells issuing from one or more similar cells, but the filamentous ramifying extension of the parent cell or cells. Moreover, when mature, it is composed of two phases: the vegetative substratum mycelium, and the aerial sporogenous mycelium. Recent work by von Plotho (1940)~ Klieneberger-Nobel (1947), and Erikson (1947a), has confirmed the existence of constitutional differences ' between these phases, already suggested by the studies of 0rskov (1923). It follows, therefore, that in a discussion of variation, such as the frequent phenomenon of asporogenous sectors produced within a single colony, it is essential to consider the origin of the inoculum in every instance. With very few exceptions, this has not been done by students of this particular problem.Actinomyces coelicolor was selected as the test organism for this study for the following reasons. (1) Like many other saprophytic actinomycetes, it readily produces asporogenous sectors or discrete sporeless colonies on certain media ; (2) it is strikingly pigmented, the range of colours varying with the pH achieved by the growth of the organism (Oxford, 1946; Cochrane & Conn, 1947) and therefore [yielding a partial index of metabolic activity; ( 8 ) some

Section: Discussionmentioning

confidence: 99%

Differentiation of the Vegetative and Sporogenous Phases of the Actinomycetes

Erikson¹

1948

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“…For plating bacteria and actinomycetes a non-selective medium, based on the 'artificial soil solution' used by Erikson (1947) From the sieved soil 10 g. were taken to make the primary suspension from which further dilutions were made in 0.75 % (w/v) NaCl. Five replicate plates were made at a final dilution of 1/250,000 using 15 ml.…”

Section: 'Methodsmentioning

confidence: 99%

A Comparison of a Direct- and a Plate-counting Technique for the Quantitative Estimation of Soil Micro-organisms

Skinner

Jones

Mollison

1952

137

SUMMARY:Estimates of numbers of micro-organisms occurring in three differently manured soils, made by a direct-counting and plating technique, were compared. No correlation was found between the two methods and reasons for the large discrepancy between them are discussed. Contradictory information of the effect of external factors on soil micro-organisms can be given by the two different methods of counting.Estimates of the total numbers of bacteria in soil obtained by a direct-counting technique devised by Jones & Mollison (1948) are of the order of several thousands of millions/g. soil, while estimates by conventional plating methods are in tens of millionslg., even on the least selective media so far used. The same authors found a difference of the same kind between the quantity of fungal mycelium in soil as estimated by a direct count of number of pieces/g. as compared with colony plate counts, although in this comparison the former count is only 2-6 times greater than the latter.The effect of external factors such as soil moisture and temperature on the various groups of soil microflora has been investigated by several workers and, while certain correlations have been found, the results have been conflicting. The estimations of numbers of organisms were mainly based on plate counts. The present investigation was undertaken to compare direct counts with plate counts over a period of time, to determine how these varied with soil moisture and temperature and to show whether these two counting methods did, in their different ways, give the same sort of information about the soil population. The soils of three differently manured plots were sampled at intervals (Fig. 1) over the greater part of a year, and determinations made of the moisture content of these samples and of their bacterial, fungal and actinomycetal populations, by plating and a direct-counting technique. 'METHODSSoil sampZing. The soil samples were taken from three of the classical plots of Broadbalk field, which has grown wheat continuously for just over 100 years and whose plots have had different manurial treatments over that period.Plot 2 (farmyard manure), plot 3 (no manure) and plot 7 (complete minerals + ammonium sulphate) were sampled at intervals between January and December. Soil was collected by an auger to a depth of 4 in. in 12 areas on each plot; these were bulked and passed through a 3 mm. sieve. From these sieved samples the necessary amounts of soil were taken for the determination

“…Moreover, wild streptomycetes in soil show the same characteristic mode of growth when developing on buried coverslips (see Erikson, 1947: pl. 1, fig.…”

Section: Eriksonmentioning

confidence: 99%

“…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. …”

mentioning

confidence: 99%

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

Erikson

1955

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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.