Mechanisms of low-dose nZVI induced microbial community evolution: extracellular secretion and key transcriptional response

Nano zero-valent-iron (nZVI) has shown considerable potential to improve conventional biological treatment processes. Designing low-dose exposure strategies is critical for biological nanosystems to avoid oxidative stress and subsequent inhibitory reactions. However, knowledge gaps remain in exploring adaptive evolutionary theories of low-dose exposure strategies, particularly in understanding the full complexity of transcriptional responses. In this study, systemic metrics and extracellular secretion behaviour were analysed holistically. A self-organising mapping network algorithm was introduced to reveal key transcriptional patterns under low-dose nZVI exposure. Low-dose nZVI induced extracellular secretion as the response pioneer, and the relatively high protein content and homogeneous network structure formation in the tight-binding layer extracellular polymer (TB-EPS) adequately revealed structural variability in the core interaction region. Moreover, the characteristic responses of redox activity and energy exchange were inferred to underlie the transcriptional pattern of low-dose exposure. In contrast, the characteristic response pattern to high doses of nZVI suggests a range of repair and adaptation processes in the microbial community. These findings highlight a unique evolutionary mechanism for low-dose nZVI exposure and deepen our understanding of the selection of nZVI binding strategies by biological treatment processes.