Interactions of microbial biofilms with metal nanoparticles in the context of bioremediation.

Microbial biofilms are of growing interest in the field of bioremediation due to their stress resistance and high biodegradation activity. On the other hand, metal nanoparticles (MNPs) are increasingly being used as effective catalysts for the binding of heavy metals and the dehalogenation of persistent organic pollutants. The present review is aimed at the comprehensive analysis of beneficial biofilm interactions with MNPs in the context of bioremediation applications. Particular emphasis is placed on the concentration-dependent nature of these interactions, where low doses of MNPs stimulate the metabolic activity of biofilms, while high doses exert toxic effects. The proposed mechanisms of low-dose stimulatory effects of MNPs include: (i) enhanced cell adhesion, changes in the extracellular polymeric substance (EPS) composition and increased biosurfactant activity possibly regulated by a quorum sensing system, (ii) induction of moderate oxidative stress that activates metabolic processes, including antioxidant systems and catabolic pathways, (iii) improving electron transport in the biodegradation system by serving as electron donors or electron shuttles, (iv) direct enzymatic reduction of metal ions within the biofilm matrix, leading to the formation of biogenic MNPs and hydrogen, which are involved in the reductive decomposition of organic pollutants and the immobilization of toxic metals. Practical applications of hybrid nanobiosystems for the removal of various pollutants, as well as environmental risks and future prospects are discussed.