The Microbiological Activity of Soil in Response to Gliotoxin, the “Lethal Principle” of Trichoderma

Abstract

Trichoderma is a soil-dwelling microorganism that has many benefits for plants and is therefore widely used in agriculture. Among the secondary metabolites produced by Trichoderma, gliotoxin (GT) is one of the most studied. The antagonistic effect of GT on other fungi was first discovered by R. Weindling in 1934. He referred to it as the “lethal principle” of Trichoderma. Despite the long history of studying GT, its impact on the soil microbial community has remained largely unexplored. In our work, we investigated the response of the soil microbial community to different doses of GT (10–500 µM per kg) and different durations (7–56 days) of exposure. We measured microbiological parameters (CO2 emission, microbial biomass (MB)), calculated the eco-physiological indices and determined the activity of soil enzymes involved in the C, N, P and S cycles. We identified three types of microbial responses to GT: inhibition, stress and stimulation. The inhibitory effect developed only by day 56 and in the samples treated with 500 μM GT. The stress effect (increased CO2 emission and decreased MB) of GT on microbial communities was predominant. Soil extracellular enzymes also responded to GT to varying degrees. A stimulating effect of GT on enzyme activity was noted for β-D-1,4-cellobiosidase and β-1,4-glucosidase. The activity of arylsulfatase and leucine aminopeptidase decreased under the influence of GT up to day 28, but by the end of the experiment, there was a restoration of activity. We did not observe any significant changes in the activity of β-1,4-xylosidase, β-1,4-N-acetyl-glucosaminidase or acid phosphatase. The results obtained showed that GT at high, “man-made” doses can inhibit the microbiological activity of soil, but at naturally occurring concentrations, it can have a stimulating effect on soil microbiome functionality.