A broad-spectrum analysis of the effects of teflubenzuron exposure on the biochemical activities and microbial community structure of soil

We evaluated the response of soil bacteria to applications of the insecticide teflubenzuron at the field rate dosage (FR; 0.15 mg/kg of soil) and at a higher dosage (10*FR; 1.5 mg/kg of soil). When applied at the FR dosage, teflubenzuron had no effect on several biochemical parameters of the soil, including substrate-induced respiration (SIR), dehydrogenase (DHA) and phosphatase activities (PHOS), and N–NO3− and N–NH4+ concentrations. Additionally, no differences were observed in the culturable fraction of the soil bacteria (the number of heterotrophic, nitrifying, denitrifying and N2-fixing bacteria; the growth strategy; the ecophysiological and colony development indices; and the physiological state). In contrast, treatment with the 10*FR dosage of the insecticide significantly increased SIR, DHA, PHOS and N–NH4+ levels and the number of heterotrophic and denitrifying bacteria. Decreases in urease activity (URE) and the number of nitrifying and N2-fixing bacteria were also observed. A phospholipid fatty acid (PLFA) method-based analysis of the entire soil microorganism population revealed that teflubenzuron treatment affected the total fatty acid level as well as those considered to be of Gram-positive bacteria, Gram-negative bacteria and fungi. This effect was observed on days 1 and 14 post-treatment. A principal component analysis (PCA) of the PLFAs showed that teflubenzuron treatment significantly shifted the microbial community structure; however, all of the observed effects were transient. Studies on the degradation of teflubenzuron revealed that this process is characterised by a short lag phase and a rate constant (k) of 0.020/day. This degradation rate follows first-order kinetics, and the DT50 was 33.5 days. This is the first study that thoroughly examines the functional and structural status of both the culturable and non-culturable fractions of the soil microbial community after teflubenzuron application.

► Multi-approach analyses of soil bacteria after teflubenzuron application were performed. ► The field rate (FR) application of teflubenzuron had no effect on the soil bacteria. ► Teflubenzuron, applied at 10*FR, changed several biochemical parameters of the soil. ► Nitrifying and N2-fixing bacteria were sensitive to a 10*FR dosage of teflubenzuron. ► PLFA patterns revealed alterations in the microbial community structure of the soil.