Impact of silver nanoparticles on natural marine biofilm bacteria

The use of nanoparticles has increased dramatically in recent years, with silver being the most widely used in consumer and medical products. Silver is a known bactericide and is found in goods such as cosmetics, surfaces, plastics and clothing. This increases their potential release and accumulation in the environment. Bacteria in nature are largely found as biofilms and perform or contribute to a number on essential environmental processes, and are at risk from the accumulation of silver nanoparticles.

The authors of this paper investigated the impact of well characterised silver nanoparticles to natural marine biofilms.

Biofilms were grown on acid-washed and sterilised glass slides at the western marina of Singapore during September and October 2007. The slides were placed parallel to each other using plastic frame holders to separate them by approximately 1cm. Holders were then submerged for 3 days at a depth of around 1m. After the three days, the biofilms were transported to laboratories in seawater.

Silver nanoparticles in the seawater were characterised (using a number of methods, which are discussed in the paper, but wouldn’t fit into this blog).

Extracellular polymeric substances were lectin stained to quantify the effects of silver nanoparticles on marine biofilms and examined, analysing silver content and the genetics of the bacterial community present.

Even though the biofilms were grown in an industrious harbour, the background levels of silver in sea-water were always below the limits of detection. The amount of silver uptake by the biofilms per unit of volume was between 1.3- 2.1 and 17.1- 19.5 for 20µg L^-1 and 200µg L^-1, and almost 10 times greater for 2000µg L^-1 which was 172.6- 235.2. These results show a linear dose dependence.

The investigators then checked for the effects of the silver nanoparticles on the biofilms. This was done by fluorescent labelling with site-specific lectins and examined using ISA-2. The 4 day old biofilms (exposed for 24h to 200µg L^-1 and 2000µg L^-1 of silver nanoparticles) had a significantly lower volume and biomass than controls of the same age; although there was no significant difference between the controls and biofilms exposed to 20µg L^-1.The results obtained in this study strongly show effects on marine biofilms of waterbourne exposure to silver nanoparticles. Exposure and uptake of silver nanoparticles at concentrations over 200µg L^-1 creates an overall thinning effect on the biofilm and molecular analysis displayed thatb the highest concentration of silver nanoparticles impeded biofilm colonisation and development.

Fabrega, J., Zhang, R., Renshaw, J. C., Liu, W-T., Lead, J. R., 2011. Impact of silver nanoparticles on natural marine biofilm bacteria. Chemosphere. 85 (6): 961-966.