Production of Gliotoxin in Unsterilized Soil
IT has long been recognized that microbial antagonisms exist in the soil, and the possibility that this might be due to production of antibiotics has been suggested although never actually proved.
Antibiotic production by fungi on organic manures and in soil.
Penicillium patulum, Aspergillus clavatus and A. terreus produced antibiotic substances when grown on organic materials which are used or could be used as manures. The addition of glucose increased the antibiotic titre in every case. Antibiotics were also formed in autoclaved soils enriched with easily available carbon sources and inoculated with one of the following fungi: P. patulum, A. clavatus, A. terreus and two unidentified species of Penicillium. P. patulum formed an antibiotic also on partially sterilized supplemented soil. The degree of antibiotic activity was decreased when soil cultures of P. patulum were contaminated with other organisms from soil or from the air, but even gross contamination with natural soil at 25° did not destroy activity entirely until 11 days had elapsed. Loss of activity was smaller at lower temperatures.
Evaluation and Control of Collapsible Soils
Some compacted soils wetted under certain conditions of compaction and loading may exhibit additional settlement (collapse). To investigate the effect of the soil type, compaction water content, initial dry unit weight and applied pressure at wetting on collapse potential, 138 single‐oedometer tests were conducted on eight different soils. The results indicate that well‐graded soils tend to collapse more than poorly graded ones under similar conditions. Furthermore, collapse potential decreases with an increase in (1) The difference between the sand and clay percentages; (2) compaction water content; and (3) initial dry unit weight, while it increases with pressure at wetting. A multiple regression analysis was performed on the laboratory results to provide a collapse‐predictive model that was substantiated by data reported by several researchers. A chart is presented to estimate (1) The collapse potential of soils under various conditions; and (2) the critical water content beyond which no collapse is ex...