Archive for the ‘Reviews’ Category

Bacteria go on a DIET

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.

Read the Critical Review for free* today:

Hardwiring microbes via direct interspecies electron transfer: mechanisms and applications
Qiwen Cheng and Douglas F. Call
Environ. Sci.: Processes Impacts, 2016,18, 968-980
DOI: 10.1039/C6EM00219F

*Access is free until 23/09/2016 through a registered publishing personal account.

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Critical Review: Measuring the flow of silver nanoparticles through the environment

silver nanoparticles in the environmentThis 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

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HOT Perspective on assessing exposure of aquatic environments to nanoparticles

nanoparticles, environment, risk assessmentAntonia Praetorius et al. from ETH Zurich, Switzerland, and Chalmers University of Technology, Sweden, present a research agenda in this Perspective article to maximise effective risk assessment of engineered nanoparticles (ENPs) in aquatic environments.

They consider the huge complexity of the task ahead in their discussion, recommending that the main components of exposure are identified, the approach is simplified and that the most environmentally relevant materials are prioritised. Their discussion involves: 

  1. A simplified approach – grouping ENPs by size, product type, emission and fate
  2. Identifying external parameters that effect exposure such as pH to give appropriate experimental conditions for assessment
  3. Modelling – ability to test different scenarios and predictions of emissions; fate and exposure; bottom-up and top-down approaches
  4. Combining modelling and experiments

They emphasise the importance of a collaborative approach with a feedback loop between modelling and experiments and consensus on grouping and parameters.

This Perspective is free to access for the next 4 weeks*. Read the authors’ vision for risk assessment of engineered nanoparticles now by clicking the link below:

Facing complexity through informed simplifications: a research agenda for aquatic exposure assessment of nanoparticles
Antonia Praetorius, Rickard Arvidsson, Sverker Molander and Martin Scheringer
DOI: 10.1039/C2EM30677H

*Free access to individuals is provided through an RSC Publishing personal account. Registration is quick, free and simple

 

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Perspective – TiO2 nanoparticles and carbon nanotubes in aquatic environments

Two cases studies – those of titanium dioxide nanoparticles and carbon nanotubes – are used to investigate the impact of man-made nanomaterials in aquatic environments in this Perspective.

In particular, the authors from U. S. Environmental Protection Agency and the University of California focus on nanomaterial production methods and attempt to resolve the inconsistencies and contradictions in data that arise from different sources and synthesis methods. They look at the key material properties that influence the nanomaterials’ impact on the environment.

This Perspective includes detailed data and discussion of: 

  1. Production processes
  2. Crystallinity, charge, morphology and composition
  3. Aggregation and solution chemistry
  4. Transport in porous media

This Perspective presents an in-depth investigation with wider discussion and review of TiO2 nanoparticles and carbon nanotubes. It’s free to access* for the next 4 weeks, so have a read here:

Effects of dominant material properties on the stability and transport of TiO2 nanoparticles and carbon nanotubes in aquatic environments: from synthesis to fate
Xuyang Liu, Gexin Chen, Arturo A. Keller and Chunming Su
DOI: 10.1039/C2EM30625E

*Free access to individuals is provided through an RSC Publishing personal account. Registration is quick, free and simple

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