March 20th, 2006



A unique biological visualization library

Digital Morphology, part of the National Science Foundation Digital Libraries Initiative, develops and serves unique 2D and 3D visualizations of the internal and external structure of living and extinct vertebrates, and a growing number of 'invertebrates'. The Digital Morphology library contains nearly a terabyte of imagery of natural history specimens that are important to education and central to ongoing cutting-edge research efforts.


Can Bacteria 'Talk' Through The Air?

A study reveals that physically separated colonies of Escherichia coli can communicate using airborne signals, allowing antibiotic resistance to be conferred between populations. The groundbreaking finding, published in the Journal of Applied Microbiology, may help explain how bacterial biofilms multiply and spread in the presence of antibiotics, say the authors.
Bacteria are known to use intercellular signalling mechanisms to regulate gene expression in response to changes in their environment, and recent studies have suggested the presence of a ‘sonic’ signal that allows messages to be transmitted without the need for a physical link.
Richard Heal and Alan Parsons, from science and technology company QinetiQ, analysed intercellular signalling between discrete populations of E. coli in Petri dishes. The populations were separated by a plastic dividing wall of 1.22 mm thickness, with a 5 mm gap between the wall and lid to allow air to circulate.

First, growth culture was placed in one half of the bipartite Petri dish and inoculated with E. coli, to form a ‘signalling’ population. When ampicillin was added to the culture, all colonies died.
Next, the experiment was repeated, but with a second population of E. coli on growth medium in the neighbouring compartment. This time, the colonies in the first compartment not only survived, but actually multiplied.

‘Transfer of the growth-promoting signal resulted in the induction of resistance to the antibiotic ampicillin,’ the team explains. However, when the passage of air between the two populations was prevented, there was a complete cessation of the growth-promoting effect.
Although the exact nature of the signal remains to be determined, the authors are confident that it does not involve the production of autoinducer-2 from the luxS gene. ‘Signal transmission is likely to involve airborne transfer of a signal species,’ they state. ‘Based on extracellular factors already identified in E. coli, the most likely candidate is indole.’
Heal and Parsons conclude: ‘Our findings may represent a mechanism by which multiplication and spreading of a bacterial biofilm could occur under antibiotic stress.’

original full text paper:
Journal of Applied Microbiology, June 2002
Novel intercellular communication system in Escherichia coli that confers antibiotic resistance between physically separated populations

На предмет использования бактериями ультразвука в качестве средства коммуникации опыты проводились ранее, в частности в Токийском университете.

Cellular signals regulating antibiotic sensitivities of bacteria
The effects of bacterial masses upon the drug resistance of neighboring bacteria were investigated. The experiments were performed with plastic Petri dishes divided into two identical compartments. A growing mass of Bacillus subtilis (signal emitter cell) in one compartment exerted enhancing effects upon the erythromycin and streptomycin resistance of Bacillus carboniphilus (signal recipient) cells, sparsely seeded in the other compartment, through the plastic wall and the air. These effects of the growing mass of cells are attributed to the emission of "sonic" signals.

Growth-promoting effect of carbon material upon bacterial cells propagating through a distance
Carbon material such as graphite and activated charcoal, but not diamond, causes the promotion of growth of certain bacteria under ordinarily non-permissive stress conditions over a distance of several centimeters. Bacillus carboniphilus under the stress of a high KCl concentration and high temperature responded to this remote effect of carbon material with enhanced growth, and thermophile bacterium Bacillus stearothermophilus responded similarly yet moderately under the stress of low temperature. The remote effect of carbon was caused by its activation with external energy, probably of electromagnetic nature, as this effect was markedly decreased by sheltering the experimental system with an iron or aluminum barrier. Carbon material probably transforms the external oscillatory pulses or radiation into a signal exerting, far-reaching, growth-promoting effect upon cells. The most plausible candidate of signals emitted from carbon was considered to be (ultra)sonic.

Production of sound waves by bacterial cells and the response of bacterial cells to sound
Bacterial cells enhance the proliferation of neighboring cells under stress conditions by emitting a physical signal. Continuous single sine sound waves produced by a speaker at frequencies of 6-10, 18-22, and 28-38 kHz promoted colony formation by Bacillus carboniphilus under non-permissive stress conditions of high KCl concentration and high temperature. Furthermore, sound waves emitted from cells of Bacillus subtilis at frequencies between 8 and 43 kHz with broad peaks at approximately 8.5, 19, 29, and 37 kHz were detected using a sensitive microphone system. The similarity between the frequency of the sound produced by B. subtilis and the frequencies that induced a response in B. carboniphilus and the previously observed growth-promoting effect of B. subtilis cells upon B. carboniphilus through iron barriers, suggest that the detected sound waves function as a growth-regulatory signal between cells.


Switch on & off mechanism in genes discovered!

genes in chromosomes have a "switch on and off" system working through the RNA interference (RNAi), which plays a vital role in development of the animal and human body. "Genes in chromosomes switch on and off like electrical switches and play a role in the development of body. Genes placed in two different areas normally express, but when they require to switch off in the developmental body part, they come closer".
The finding suggests that fascinating mechanism of RNAi machinery not only influences the regulations of a specific gene but also helps in bringing genes from different chromosomes together, which is essential for growth and maintenance of organisation.

"This is a major contribution by our paper. We first show that developmental protein is controlled by switch on and off mechanism and that is regulated by chromosomal long distance interaction of different identical genes of different chromosomes. Different chromosomes in different places normally express themselves and if they need to switch off they come closer together and silence".
"In appearance fruitfly and humans are way apart, but they have many similarities and body plans", said Utpal Bhadra. Citing example of how the switch on and off of genes by RNAi affect development of the body, Utpal Bhadra said when two particular genes, involved in the development of the wing of the fly, were brought together, it led to their silencing and growth of wing became distorted. But when the same genes were restored to their original positions, growth of the wing became normal.

Cell, March 2006
RNAi Components Are Required for Nuclear Clustering of Polycomb Group Response Elements