Impact of cycloheximide addition on adenylates in soil

Cycloheximide inhibits specifically the ribosomal protein synthesis of eukaryotic cells, i.e. the metabolism of soil fungi. We measured cycloheximide effects on adenylates in 20 different soils (0–10 cm depth) from arable, grass and forest land with a large variety of soil properties. The aims were (1) to assess the interactions between cycloheximide effects and soil properties and (2) to prove the relationship between cycloheximide effects on ATP and the ergosterol-to-microbial biomass C ratio, which is an indicator for the fungal proportion of the total microbial biomass. The adenylates ATP, ADP and AMP were measured 6 h after adding either 10 mg cycloheximide per gram soil in combination with 24 mg talcum per gram soil or 24 mg talcum per gram soil solely. The medians of the relative increases in AMP and ADP were 45 and 25% and the medians of the relative decreases in ATP and adenylates were −36 and −12%. These changes in adenylate composition lead to a cycloheximide-induced relative decrease in the adenylate energy charge level of 15%. The relative decrease in ATP content after cycloheximide addition was significantly correlated with the ATP-to-microbial biomass C ratio, but not with the ergosterol-to-microbial biomass C ratio. The absolute increase in ADP and the absolute decrease in ATP were affected by the clay content according to principal component analysis. The reduction of the ATP-to-microbial biomass C ratio indicates that this ratio had the potential of being an important ecotoxicological indicator of direct toxic effects of organic pollutants on soil microorganisms.