New methods to visualize bacterial cell-to-cell communication

Most bacteria are able to communicate with each other by secreting signaling molecules. Once the concentration of signals has reached a critical density (“the Quorum), the bacteria are able to coordinate their behavior. Only when this critical population density has been reached certain genes are activated that lead to, for example, the formation of biofilms or the expression of virulence factors. Bacteria utilize this so-called “Quorum Sensing” (QS) to synchronize their behavior to regulate functions that benefit the entire population.

The most commonly used signaling molecules are N-Acyl-L-homoserine lactones (AHLs) that are secreted by the bacteria into their surroundings, where they can easily be incorporated by other cells. The AHLs then start binding to specific QS-receptors once a certain density has been reached inside the cell.

New methods to visualize bacterial cell-to-cell communication

Selective labeling of the Burkholderia cenocepacia quorum-sensing receptor CepR.Credit: José Gomes et al.,

Read more at:

Fluorescent labeling of signaling compound to visualize receptors

The research groups under the leadership of Prof. Karl Gademann (University of Basel) and Prof. Leo Eberl (University of Zurich) have succeeded in visualizing live cell-to-cell communication pathways. The scientists added fluorescents tags to natural AHL signaling molecules and were able to show through tests with bacterial cultures that the modified signaling molecule selectively binds to the Burkholderia cenocepacia QS receptor.

B. cenocepacia is a member of a bacterial group known to form  in the lungs of immunocompromised persons or patients suffering from , causing severe complications such as pneumonia.

The scientists were also able to detect the receptor in a native population of B. cenocepacia. Here, the natural AHL signaling molecule is competing with its artificial analogue for the binding to the receptor. The fluorescent-labeling agent was equally distributed over the live cell, which made it possible to localize the receptor inside the  for the first time.

Broad application possibilities

Using fluorescently labeled AHL analogues represent an operationally simple tool for the imaging of QS receptors in live cells. Thus, this new method could be used for a broad range of applications, such as the fast analysis of QS in various environmental and clinical samples. Furthermore, it might lead to a better understanding of the communication between bacteria and host as well as of the cell-to-cell communication in bacteria populations.

 Explore further: Signaling receptor may provide a target for reducing virulence without antibiotics

Cranial irradiation causes brain degeneration

Cranial irradiation saves the lives of brain cancer patients. It slows cancer progression and increases survival rates. Unfortunately, patients who undergo cranial irradiation often develop problems with cognitive functioning. To determine how radiation affects cognition, Vipan Parihar and Charles Limoli of the University of California, Irvine studied cranial irradiation in mice. They found that exposure to radiation causes degenerative changes to brain architecture similar to those observed in people with neurodegenerative conditions such as Alzheimer’s disease and Huntington’s disease. Their research appears in the Proceedings of the National Academy of Sciences.

Radiation therapy is the routine frontline treatment for almost all forms of pediatric and  cancer because of its ability to forestall tumor growth. While it increases the lifespans of people diagnosed with brain cancer, cranial irradiation can reduce quality of life by causing irreversible cognitive impairment. Central nervous system (CNS) exposure to radiation causes problems with memory, learning, attention, processing speed and executive function.

To understand how reduces cognitive ability, Parihar and Limoli exposed mice to either 1 or 10 Gy of radiation, doses much lower than the maximum dose the CNS can withstand before tissue damage occurs. After 10 or 30 days, the researchers killed the mice and dissected their brains. They then examined the hippocampus, which is associated with learning and memory.

Parihar and Limoli observed dose-dependent reductions in the area, length and branching of dendrites, projections on neurons that send and receive signals to and from other neurons. These reductions persisted after 30 days. The number and density of dendritic spines, bulbous extensions on dendrites, also decreased. Dendritic spines regulate CNS connectivity, are associated with memory storage and play an important role in mediating . There is a positive correlation between number of dendritic spines and synaptic density, which in turn correlates with cognitive ability. The researchers also identified significant changes in levels of pre and post-synaptic proteins.

Reduced dendritic complexity is a characteristic of Alzheimer’s disease, Huntington’s disease, recurrent depressive illness and epilepsy. Dendritic spine abnormalities are associated with Huntington’s disease, temporal lobe epilepsy, AIDS-related dementia, Down syndrome, Rett syndrome and Fragile-X syndrome.

Parihar and Limoli state that the reduction in dendritic spine density and the persistence of degenerative changes after one month is consistent with the irreversible reduction in cognitive functioning experienced by brain cancer survivors who have had cranial radiotherapy.

Cranial irradiation causes brain degeneration

Cranial irradiation is used routinely for the treatment of nearly all brain tumors, but may lead to progressive and debilitating impairments of cognitive function. Changes in synaptic plasticity underlie many neurodegenerative conditions that correlate to specific structural alterations in neurons that are believed to be morphologic determinants of learning and memory. To determine whether changes in dendritic architecture might underlie the neurocognitive sequelae found after irradiation, we investigated the impact of cranial irradiation (1 and 10 Gy) on a range of micromorphometric parameters in mice 10 and 30 d following exposure. Our data revealed significant reductions in dendritic complexity, where dendritic branching, length, and area were routinely reduced (>50%) in a dose-dependent manner. At these same doses and times we found significant reductions in the number (20–35%) and density (40–70%) of dendritic spines on hippocampal neurons of the dentate gyrus. Interestingly, immature filopodia showed the greatest sensitivity to irradiation compared with more mature spine morphologies, with reductions of 43% and 73% found 30 d after 1 and 10 Gy, respectively. Analysis of granule-cell neurons spanning the subfields of the dentate gyrus revealed significant reductions in synaptophysin expression at presynaptic sites in the dentate hilus, and significant increases in postsynaptic density protein (PSD-95) were found along dendrites in the granule cell and molecular layers. These findings are unique in demonstrating dose-responsive changes in dendritic complexity, synaptic protein levels, spine density and morphology, alterations induced in hippocampal neurons by irradiation that persist for at least 1 mo, and that resemble similar types of changes found in many neurodegenerative conditions.

RNA-interference pesticides will need special safety testing

Standard toxicity testing is inadequate to assess the safety of a new technology with potential for creating pesticides and genetically modifying crops, according to a Forum article published in the August issue of BioScience. The authors of the article, Jonathan G. Lundgren and Jian J. Duan of the USDA Agricultural Research Service, argue that pesticides and insect-resistant crops based on RNA interference, now in exploratory development, may have to be tested under elaborate procedures that assess effects on animals’ whole life cycles, rather than by methods that look for short-term toxicity.

RNA interference is a natural process that affects the level of activity of genes in animals and plants. Agricultural scientists have, however, successfully devised artificial “interfering RNAs” that  in , slowing their growth or killing them. The hope is that interfering RNAs might be applied to crops, or that crops might be genetically engineered to make interfering RNAs harmful to their pests, thus increasing crop yields.

The safety concern, as with other types of genetic modification and with pesticides generally, is that the artificial interfering RNAs will also harm desirable insects or other animals. And the way interfering RNA works means that simply testing for lethality might not detect important damaging effects. For example, an interfering RNA might have the unintended effect of suppressing the action of a gene needed for reproduction in a beneficial species. Standard laboratory testing would detect no harm, but there could be  in fields because of the effects on reproduction.

Lundgren and Duan suggest that researchers investigating the potential of interference RNA pesticides create types that are designed to be unlikely to affect non-target species. They also suggest a research program to evaluate how the chemicals move in real-life situations. If such steps are taken, Lundgren and Duan are optimistic that the “flexibility, adaptability, and demonstrated effectiveness” of RNA interference technology mean it will have “an important place in the future of pest management.”