Common Soil Fungi Research Articles

The incidence of apatite-solubilizing organisms in the rhizosphere and soil

A number of microorganisms capable of solubilizing apatite mere isolated from soil and from the rhizosphere of plants. Many genera of common soil fungi and bacteria were represented. The organis~ns solubilizing apatite were consistently present in higher proportions in rhizosphere isolates than in those from nearby soil. The zone of solution of apatite surrounding colonies on agar plates was usually characteristic of organisms producing acid in liquid culture; however, the degree of solubilization was not proportional to the fall in pH. On subculturing, many isolates rapidly and irreversibly lost their ability to dissolve apatite. Soil isolates lost their ability to solubilize apatite more readily than isolates from the rhizosphere.

Survival and recolonization by fungi in soil treated with formalin or carbon disulphide

In samples of soil taken 3 weeks after treatment with dilute formalin (1:500 to 1:1000), Trichoderma viride had established itself as the dominant fungus, and this dominance persisted during the 6 months period of sampling. On agar, T. viride was more tolerant of formalin than were seven other common soil fungi. T. viride also became dominant after treatment of soil with carbon disulphide, at the rate of 0·5 ml./250 g. moist soil. After higher dosages (1 to 10 ml. carbon disulphide), the dominant fungi were two Ascomycetes, Penicillium luteum and Aspergillus fischerii, which were found to be highly tolerant of carbon disulphide in vitro, by comparison with other fungi tested. Recolonization of soil sterilized, by intermittent steaming, from an inoculum of unsterilized soil was followed by means of the ‘soil recolonization tube’, which comprises an 18 in. length of tube with seven side-arms at 2 in. intervals. From the side-arms, which were protected from outside contamination by metal caps, micro-samples of soil were taken at intervals for the making of soil plates, and in this way the progress of soil colonization by fungi along the length of the main tube could be followed. In closely packed soil, the first fungal colonizers were fast-growing Phycomycetes, but in loosely packed soil, their place was usually taken by Trichoderma viride. Soil recolonization tubes were also used to study the movement of formalin and carbon disulphide, respectively, through the soil. Distribution of the fumigant, which was injected at the central side-arm, was determined after an interval by taking samples of soil for plating from the side-arms on either side of it.

Viridin

VIRIDIN, an antibiotic produced by a pigment-forming strain of the common soil fungus Trichoderma viride, was first described by Brian and McGowan1, and Brian, Curtis, Hemming and McGowan2. Viridin is not anti-bacterial but is highly antifungal. Its activity against certain fungi is remarkably high. Germination of the spores of, for example, Botrytis allii is prevented by a concentration of 0.019 p.p.m. of α-viridin or 0.156 p.p.m. of β-viridin. Among synthetic fungicides, only the organo-mercurials are of the same order of activity.

The Biological Decomposition OF Plant Materials: Part IV. The Biochemical Activities on Straws of Some Cellulose‐Decomposing Fungi

Summary1. A number of common soil fungi isolated from rotting straw were inoculated into sterile straw with the addition of available nitrogen.2. The amount of decomposition effected, the losses of various straw constituents, and the immobilisation of nitrogen which took place, were all determined, and compared with mixed flora decompositions at various temperatures.3. Though none of the organisms develop appreciably on a cellulose‐agar plate, all were found to decompose cellulose to a considerable extent.4. Certain minor differences in ability to utilise the carbohydrate constituents were noted, but in general all substances but lignin were attacked to a degree relatively proportional to the apparent total loss of organic matter.5. The “nitrogen factor” or nitrogen immobilised by 100 gm. straw rotting with a particular organism was determined in each case. There is no correlation between the “nitrogen factor” and the loss of organic matter or of any particular straw constituent. The differences appear to be varietal.6. Some indication of the relative efficiencies of the organisms was obtained from a factor for which the name “nitrogen equivalent” is proposed. This represents the nitrogen immobilised as microbial protein in the course of the removal of 100 gm. organic matter from any given plant material.7. Attention is drawn to difficulties which restrict the absolute value of the “nitrogen equivalent” as a measure of efficiency in decomposition.8. The value of single factor studies as a preliminary to the synthetic method of investigation of such a process as biological decomposition is discussed.The author‐is indebted to Sir John Russell, F.R.S., Director of the Rothamsted Experimental Station, for placing at his disposal the facilities of that Station, and to the Department of Scientific and Industrial Research for a Senior Research Award, during the tenure of which this work has been carried out.Especially are his thanks due to Dr W. B. Brierley, and Mr E. H. Richards, Heads of the Departments of Mycology and Fermentation, for their ready assistance and advice.