ACTINOMYCETES IN DANISH SOILS

Abstract

Counts were made of actinomycetes in 56 Danish soils of different character. The numbers ranged from none or a few thousands to about 13 millions per gm. of soil. Nearly all strongly acid soils (pH less than 5) had very small numbers. The highest numbers seemed most frequent at pH 6.8-8. The % of actinomycetes in the total microflora on plates was 0-73%; this figure was very low in strongly acid peat soils; otherwise it showed no correlation with soil reaction. Apart from the reaction, there seemed to be no correspondence between general soil type and number of actinomycetes. Several strains isolated from these soils could be recognized as belonging to the following species-groups: (1) Common[long dash]Actinomyces gri-seus, cellulosae, olivaceus, bobili, diastatochromogenus; (2) fairly common to rare[long dash]A. griseoflavus, violaceus-ruber, roseus, erythrochromogenus, pheochromogenus; new[long dash]A. fulvissimus (p. 66). The majority of the strains could not be related t6 definite groups. Strains of the same species-group often showed great differences in physiological characters, such as pigment production, ability to utilize carbohydrates, acid formation, nitrate reduction and proteolytic activity, although some of these characters remained relatively constant and appeared to have diagnostic value. Organic acids were sometimes formed from carbohydrates; this was always connected with nitrite production. On the whole, the "chromog-enous" forms had a lower proteolytic power than the non-chromogenous. The ability of actinomycetes to resist acid reaction varied widely; the final acidity produced in a physiologically acid nutrient solution for each species-group was subject to less variation than most other physiological characters and may be of value for characterization and identification.