Ingestion of metal-nanoparticle contaminated food disrupts endogenous microbiota in zebrafish

Nanoparticles and the gastrointestinal tract of zebra fish

The use of nano-particle technology is growing in favour while their effects on the environment remain relatively under studied. Materials such as Ag-NP (Silver nano-particles) are utilised by clothing companies and in food packaging because of their antimicrobial effects. This is obviously beneficial for us but what happens when these nano-particles (NP) enter the environment. As they are designed to be antimicrobial (in some cases) we can assume that they will have an effect on the microbial community. Microbes rarely exist on their own and complex relationships with other microbes as well as higher organisms exist. It’s a safe assumption that all vertebrates will have some level of microbial symbiosis for example in the gastrointestinal tract (GIT), where microbes help with the assimilation of key nutrients into the body.

A commonly studied vertebrate is the zebra fish, Danio rerio, which is used as a model organism in many studies. Using this model species Merrifield et al., (2013) investigated the effect that two of these NP had on the GIT microbiota. This was done by through feeding with either CuSO₄, AgNO₃, Ag-NP, Cu-NP or untreated food. The use of both elemental and NP forms was to differentiate between effects caused by NPs and those caused by the presence of the element. After one fortnights feeding the gut microbiota was analysed and a portion of the 16S region was amplified. From this the species richness and diversity could be determined. This was found to be highest in Cu-NP exposed fish. However this does not signify a healthy gut. In fact some key species were missing such as Cetobacterium somerae.  This microbe produces large quantities of vitamin B12 and is predicted to be a useful probiotic. The increase in diversity could then be linked to the removal of a dominant competitor. Further to this the CuSO₄ treatment had no effect on C. somerae indicating an effect of the NP not the element. Further investigation as to how this NP inhibition occurs is required.

Silver is a powerful antimicrobial agent in some environments, however neither Ag treatments had any effect. This is likely because of Ag speciation occurring in the gut lumen. High intestinal chloride concentration could be causing Ag to precipitate as silver chloride before any effect on microbiota happens. Also –SH ligands in food will bind to any ionic silver leading to low dissolved concentrations and preventing further interactions with micro organisms.

This study is the first of its kind, investigating the effect nanoparticles have on microbiota. As a preliminary experiment it opens the door for much further research into the subject. For example a metagenomic approach could be used to further identify organisms and processes affected with in the gut micrbiome. This kind of information will be useful when determining the future use of nanoparticles, i.e. how much can be released into the environment, what does this mean for wild fisheries, how can we better manage aquaculture based on this knowledge. For example this kind of work may help us to formulate feeds that incorporate nanoparticles that inhibit the growth of pathogenic organisms while promoting that of beneficial ones. To do this a much better understanding of the GIT microbiome is necessary.

Merrifield, D. L., Shaw, B. J., Harper, G. M., Saoud, I. P., Davies, S. J., Handy, R. D., & Henry, T. B. (2013). Ingestion of metal-nanoparticle contaminated food disrupts endogenous microbiota in zebrafish (Danio rerio). Environmental Pollution, 174, 157–163.