Number 852, January 3, 2008
by Phillip F. Schewe, and Jason S. Bardi
Amoebas Anticipate Climate Change
A new experiment shows that amoebas will slow their motion in synch with periodic adverse changes in their environment, and will, as if in anticipation, even slow down when the adverse condition is not delivered. A team of scientists from Hokkaido University and the ATR Wave Engineering Laboratories in Japan cultured the single-celled slime mold Physarum polycephalum (a member of the amoeba clan) in a bed of oat flakes on agar. Every ten minutes the air was made slightly cooler and drier, which had the effect of slowing the movement of the amoebas down a narrow lane. Then more favorable air would be restored and the motion continued as before.
After several cycles, the amoebas slowed even when the adverse conditions did not materialize. Later still, when the organisms have been tricked into anticipating impending climate change several times, they refrain from slowing without an actual change in conditions. One of the researchers, Toshiyuki Nakagaki from Hokkaido (nakagaki@es.hokudai.ac.jp), cautions that amoebas do not have a brain and that this is not example of classic “Pavlovian” conditioned response behavior. Nevertheless, it might represent more evidence for a primitive sensitivity or “intelligence” based on the dynamic behavior of the tubular structures deployed by the amoeba. (Saigusa et al., Physical Review Letters;11 January 2008)
Shattering Viruses
A new study is trying to establish the intrinsic vibration modes of capsids---the protein shells of virus particles that package its genetic material---with a view toward rupturing them and thereby killing the pathogenic virus. If the capsid resonant frequencies could be determined, then possibly light or sound waves might be used to shatter the capsids the way the opera singer Enrico Caruso supposedly shattered wine glasses by sustaining a note at exactly the resonant frequency of the glass. This approach to attacking viruses is alternative to treating them with chemicals, which is not always effective; furthermore, the chemicals can do damage to healthy cells, or the viruses can mutate and defeat chemical defenses. Hence the importance of attempting to undo viruses with mechanical means.
Eric Dykeman and Otto Sankey, physicists at Arizona State University, are modeling capsid vibrations at the atomic level for comparisons with experiments being performed by K.T. Tsen at ASU in which picosecond laser pulses are scattered from capsids. The capsids, which are mostly made of complex protein assemblies, will typically absorb some of the laser light, a process which causes them to vibrate. The rest of the laser beam, its energy somewhat depleted, will be downshifted in frequency. This allows observers to deduce the resonant frequency of the capsids. By staging the short laser pulse in different ways, a whole catalog of capsid resonant frequencies can be made. Sankey (otto.sankey@asu.edu, 480-965-4334) says that the simulations performed so far suggest that resonant frequencies for their chosen virus, the satellite tobacco necrosis virus (see vibration movie at http://www.aip.org/png/2008/292.htm) are in the vicinity of 60 to 90 GHz. (Dykeman and Sankey, Physical Review Letters, upcoming article)
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