Environmental Science: Processes & Impacts blog

Probably not the type of diet you are thinking of. It has something to do with food, though. I am talking about the transfer mechanisms some bacteria use to share metabolites between them, and also with bacteria of different species. In this review published in Environmental Science: Processes & Impacts, two researchers from North Carolina analyse the latest discoveries in this field, specifically in mechanisms known as DIET: “direct interspecies electron transfer”.

Scientists discovered DIET not a decade ago. Before that, only conventional diffusion models were known: an organism generated an excess of certain metabolite, released it to the surrounding media and was consumed by a second organism. This is called “mediated interspecies electron transfer” (MIET).

DIET, however, is more efficient. Instead of releasing the metabolites around, bacteria use structures that allow them to transfer chemical substances directly to other cells. These structures, usually filamentous pili full of conductive cytochromes, act as nanowires that connect bacteria to one another. However, because DIET is a form of electron transfer, sometimes proteins are not needed at all and actual electric cables may be used. When pili and cytochromes are removed in genetically engineered bacteria, they can use metal, metal oxides (such as magnetite) or activated carbon as connections. Sometimes bacteria prefer this cables to their own traditional methods: in some experiments, scientists showed that bacteria will rather connect to carbon than to other cells, probably due to the higher electric conductivity.

Nowadays we use multicellular bacterial communities in a wide variety of industrial systems from sewage treatment to energy production. Understanding how DIET interactions work is key to improve the effectiveness of these processes and will allow us to have a better control. Who knows, maybe some day DIET will lead into building intelligent bacterial circuits, the same way years ago silicon allowed us to create microchips.

This recently published article from Jing-Fu Liu et al. takes a critical view of the current investigations into the effects that silver nanoparticles have on the environment. It was published in January’s themed issue on Anthropogenic nanoparticles in the environment. 

Appropriate sampling, separation and analytical methods are vital, particularly for analysis of silver nanoparticles in complex environmental samples. This review covers: 

1. A brief history of silver colloids in the environment
2. Beneficial properties versus environmental concerns
3. Analytical techniques, including combinations of different methods, and the different sample sources, such as aerosols and soil
4. Factors and processes influencing fate and transport of AgNPs
5. Environmental transformation
6. Toxicity of silver nanoparticles and different silver species

Each of the above mentioned topics are interesting in themselves, but this article pulls the information together to give one wide perspective of the flow of silver nanoparticles through our environment and ways we can detect and analyse their effects. It highlights how much is still unknown and how complex such investigation will continue to be.

Silver nanoparticles in the environment
Su-juan Yu, Yong-guang Yin and Jing-fu Liu
DOI: 10.1039/C2EM30595J