Protistan consumers and phototrophs are more sensitive than bacteria and fungi to pyrene exposure in soil.

The levels of organic pollutants, in particular polycyclic aromatic hydrocarbons (PAHs), are increasing worldwide, yet we lack clarity on how these pollutants affect microbial communities of different trophic levels, including protists, fungi, and bacteria. Herein, we conducted soil microcosm incubation experiments to investigate the effects of pyrene, a typical PAH, on microbial communities along concentration gradients from 0 to 500 mg kg soil. Protistan communities were more sensitive to pollutants than fungal and bacterial communities, and protistan consumers and phototrophs were the dominant trophic functional groups. In addition, by assessing changes in the diversity and structure of the soil microbiome and ecological networks, we found that the microbial communities, including the protistan community and the two trophic communities composed of protists and their prey, were destabilized with increasing stress and pyrene concentrations. We identified links and complicated relationships between phototrophs, bacteria, and consumers in food webs, which explain the importance of protists in stabilizing the microbial community. Collectively, our work provides novel evidence that protists are considerably sensitive to pollution stress, and caution should be exercised in future evaluations of the protistan and multitrophic communities in polluted soil ecosystems.