Effects of low dose silver nanoparticle treatment on the structure and community composition of bacterial freshwater biofilms

Abstract

The application of engineered silver nanoparticles (AgNPs) in a considerable amount of registered commercial products inevitably will result in the continuous release of AgNPs into the natural aquatic environment. Therefore, native biofilms, as the prominent life form of microorganisms in almost all known ecosystems, will be subjected to AgNP exposure. Despite the exponentially growing research activities worldwide, it is still difficult to assess nanoparticle-mediated toxicity in natural environments. In order to obtain an ecotoxicologically relevant exposure scenario, we performed experiments with artificial stream mesocosm systems approaching low dose AgNP concentrations close to predicted environmental concentrations. Pregrown freshwater biofilms were exposed for 14 days to citrate-stabilized AgNPs at a concentration of 600 μg l-1 in two commonly used sizes (30 and 70 nm). Sublethal effects of AgNP treatment were assessed with regard to biofilm structure by gravimetric measurements (biofilm thickness and density) and by two biomass parameters, chlorophyll a and protein content. The composition of bacterial biofilm communities was characterized by t-RFLP fingerprinting combined with phylogenetic studies based on the 16S gene. After 14 days of treatment, the structural parameters of the biofilm such as thickness, density, and chlorophyll a and protein content were not statistically significantly changed by AgNP exposure. Furthermore, t-RFLP fingerprint analysis showed that the bacterial diversity was not diminished by AgNPs, as calculated by Shannon Wiener and evenness indices. Nevertheless, t-RFLP analysis also indicated that AgNPs led to an altered biofilm community composition as was shown by cluster analysis and multidimensional scaling (MDS) based on the Bray Curtis index. Sequence analysis of cloned 16S rRNA genes further revealed that changes in community composition were related with the displacement of putatively AgNP-sensitive bacterial taxa Actinobacteria, Chloroflexi, and Cyanobacteria by taxa known for their enhanced adaptability towards metal stress, such as Acidobacteria, Sphingomonadales, and Comamonadaceae. This measurable community shift, even after low dose AgNP treatment, causes serious concerns with respect to the broad application of AgNPs and their potentially adverse impact on the ecological function of lotic biofilms, such as biodegradation or biostabilization.

Subinhibitory Concentrations of Biogenic Silver Nanoparticles Affect Motility and Biofilm Formation in Pseudomonas aeruginosa

“…(2019) . Few studies, however, have investigated the subinhibitory effects of AgNPs on clinical isolates or environmental microorganisms ( Yang and Alvarez, 2015 ; Garuglieri et al., 2016 ; Grün et al., 2018 ).…”

“… Garuglieri et al. (2016) showed that treatment with AgNPs sized 14 ± 0.3 nm increased motility and Grün et al. (2018) found that treatment with 30–70 nm AgNPs enhanced biofilm formation.…”

Photodynamic Antimicrobial Action of Asymmetrical Porphyrins Functionalized Silver-Detonation Nanodiamonds Nanoplatforms for the Suppression of Staphylococcus aureus Planktonic Cells and Biofilms

“…Asymmetrical porphyrins are employed since asymmetry is known to result in high singlet oxygen quantum yield in porphyrins ( Oliveira et al, 2009 ). In addition, AgNPs and DNDS used in this work are also known for their antimicrobial potency ( Szunerits et al, 2016 ; Grün et al, 2018 ). A metal free porphyrin have been linked to Ag NPs (Ag-S bond), for antimicrobial studies ( Elashnikov et al, 2019 ).…”

Environmental context determines the impact of titanium oxide and silver nanoparticles on the functioning of intertidal microalgal biofilms

“…However, experiments conducted in more complex environments to determine if current levels of exposure to NPs are endangering microorganisms or microbial processes are more equivocal. Ag-NPs appear to have limited toxicity on the abundance of, and processes driven by, microorganisms in freshwater or estuarine biofilms, 15,[36][37][38][39] except at concentrations (1000 μg l −1 ) far higher than modelled environmental concentrations (1-100 ng l −1 ). [40][41][42] Shifts in species composition of bacterial communities have been recorded at Ag-NP concentrations of 200 μg l −1 .…”

“…[40][41][42] Shifts in species composition of bacterial communities have been recorded at Ag-NP concentrations of 200 μg l −1 . 36,39,43,44 The link between alteration of community composition by NPs and modification of associated processes is not straightforward; for instance, bacterial activity to degrade hydrocarbons can be maintained in presence of Ag-NPs, despite significant modification of the composition of the bacterial communities. 36 Toxicity of NPs to microorganisms has also been shown to be taxon specific, 37 and influenced by environmental parameters, such as presence of UV light for TiO 2 -NPs 2 and Ag-NPs, 45 and temperature for Ag-NPs.…”