Studying patterns in bacterial organization

credit to Gerard Wong, of the California NanoSystems Institute

Bacterial biofilms, at first glance, may seem to be spontaneous, random phenomena from which we have no power to protect our environment or ourselves.

They’re potentially useful as an aid to wastewater treatment, but they also cause infections that account for $6 billion a year in health care costs. Biofilms are also more resistant to antibiotic drugs, making them difficult to eradicate.

Dr. Kun Zhao, of the California NanoSystems Institute at UCLA, refuses to see biofilms as arbitrary: he emphasizes the fact that biofilms are communities of bacteria in self-produced polymeric matrices of polysaccharides, and using a biophysical approach, he studies the pattern behind their organization.

Central questions in Zhao’s research include how bacterial colonies transition from reversible to irreversible attachment, how they migrate, and how they ultimately disperse. Specifically, Zhao examines the polysaccharide Psl, which poses a positive feedback loop because it is both secreted by moving bacteria and serves as a chemo-attractant for future bacteria movement. The positive feedback creates an inherent pattern, as bacteria are more likely to visit a location they have been to before.

Zhao and colleagues have also discovered that bacterial mutants that cannot produce Psl exhibit more random and uniform movement.

To better quantify bacterial movement,Zhao has created a computer algorithm that shows the full movement history of each individual bacterium on a dish, and that provides a “search engine” allowing researchers to find every bacterium performing specific life cycle activities, like division.

Zhao has postulated a “rich get richer” mechanism for biofilms. He compares bacterial organization to Wall Street because concentrated movement ensures that some cells become extremely enriched. In the future, he hopes to model colloidal structures for biological problems, like the growth of the bacterial cell wall. Zhao currently uses colloids, which in physics are used as models for atomic systems, to observe how shapes affect self-assembly. He also would like to look at cell-substrate interactions, which are implicated in bacterial territoriality and social interactions.

by Olivia Zhu

Source: Duke University

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Drugs in the environment affect plant growth

Lettuce plants (stock image). The potential for some chemicals to influence plants is becoming increasingly relevant, particularly as waste management systems are unable to remove many compounds from our sewage. Drugs for human use make their way into soil through a number of routes, including the use of sewage sludge as fertilizer and waste water for irrigation.
Credit: © riderfoot / Fotolia

By assessing the impacts of a range of non-steroidal anti-inflammatory drugs, the research has shown that the growth of edible crops can be affected by these chemicals -- even at the very low concentrations found in the environment.

Published in the Journal of Ecotoxicology and Environmental Safety, the research focused its analysis on lettuce and radish plants and tested the effects of several commonly prescribed drugs, including diclofenac and ibuprofen. These drugs are among the most common and widely used group of pharmaceuticals, with more than 30 million prescribed across the world every day.

The potential for these chemicals to influence plants is becoming increasingly relevant, particularly as waste management systems are unable to remove many compounds from our sewage. Drugs for human use make their way into soil through a number of routes, including the use of sewage sludge as fertilizer and waste water for irrigation.

This study looked for a number of changes in edible plants, assessing factors such as water content, root and shoot length, overall size and how effectively the plants photosynthesised.

Each drug was shown to affect the plants in very specific ways, with marked differences between drugs that are closely related. For example, drugs from the fenamic acid class affected the growth of radish roots, whilst ibuprofen had a significant influence on the early root development of lettuce plants.

Dr Clare Redshaw, one of the scientists leading the project at the Medical School's European Centre for Environment & Human Health, said: "The huge amounts of pharmaceuticals we use ultimately end up in the environment, yet we know very little about their effects on flora and fauna. As populations age and generic medicines become readily available, pharmaceutical use will rise dramatically and it's essential we take steps towards limiting environmental contamination. We haven't considered the impact on human health in this study, but we need to improve our understanding quickly so that appropriate testing and controls can be put in place."

There have been growing concerns about the presence of pharmaceuticals in the environment, particularly as evidence emerges of the effects they can have on the development of animals and antibiotic resistance in bacteria. Yet their ability to affect plant growth is poorly understood.

This study marks an important step in an emerging research field attempting to assess how very low concentrations of drugs can affect the growth of crucial crop plants. It specifically considered the non-steroidal anti-inflammatory drugs tolfenamic acid, meclofenamic acid, mefenamic acid, diclofenac, naproxen and ibuprofen.

Source: University of Exeter

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