Not so precious “silver"

The production of silver nanoparticles (Ag NPs ; particles of between 1nm and 100nm in size) have increased in recent years particularly due its wide range of use. Primarily, silver nanoparticles have found applications in catalysis, optics, electronics and even medicine due to their optical, electrical and magnetic properties. Presently, most of the applications of silver nanoparticles are in antibacterial/antifungal agents in biotechnology and bioengineering, textile engineering, water treatment, and silver-based consumer products. However, the increased production also pose a potential risk to the environment in terms of bioaccumulation and bioavailability. The antibacterial action of Ag NPs could potentially have profound effects on bacterial communities. Bacteria, which primarily are found in nature as biofilms are essential for driving environmental processes such as biogeochemical cycling. In this study, Fabrega et al. ( 2011) investigated the impact of well categorized Ag NPs to natural marine biofilms.

The biofilms were grown on glass slides submerged at ≈ 1m depth for 3 days at the western marina of Singapore. Then they were transferred to the laboratory and suspended vertically in freshly collected seawater spiked with Ag NPs (20, 200 and 2000 µg/l^-1), cultures suspended vertically in seawater with no Ag NPs were used as controls. The exposure time was 24 h after which the biofilms were analysed to observe the changes to biofilm volume and mass after Ag NP exposure. The EPS were stained with lectin concanavalin and SYTO 9 (nucleic acid stain) and examined by confocal scanning laser microscope. The DNA analysis was also performed by 16S ribosomal rRNA gene polymerase chain reaction (PCR) with the use of universal primers 27F (5’-AGA GTT TGA TCC TGG CTC AG-3’), fluorescently labelled with Cy5, and 907R (5’-CCG TCA ATT CMT TTG AGT TT-3’). Terminal restriction fragment length polymorphisms (T-RFLPs) was used for profiling of microbial communities based on the position of a restriction site closest to a labelled end of an amplified gene.

The results of this study have shown that biofilm biomass and volume was significantly reduced with the increasing concentrations of Ag NPs. T-RFLP and phylogenetic analysis showed the presence of major bacterial groups in biofilms (α, γ- Proteobacteria, Flavobacteria and Cyanobacteria ) regardless of treatment with Ag NPs, therefore, even at the highest concentrations didn’t affect they distribution. Nevertheless, the succession of biofilm was inhibited by Ag NP, it affected the relative abundance of major bacterial groups in the biofilm, which can have potential longer term effects on development and function of the biofilms.

Although this study’s aims where fairly simple and authors did indicate some of the effects NPs on microbes, they haven’t really expanded on them, nor they did really suggest any wider, environmental implication of these results. Personally the whole study seemed like a lot of work and effort put in for a very little reward. Nevertheless, in general, this study was quite interesting and especially the use of T-RFLPs which allows analysis of complex bacterial communities. Since there is still little known about NP’s effects, distribution and behaviour of silver in marine systems, and with the increasing amount discharges through the incorporation of silver in NPs added to consumer goods for their antimicrobial function this research seems like a good place to start.

Fabrega et al., 2011. Impact of silver nanoparticles on natural marine biofilm bacteria. Chemosphere 85: 961–966.