August 16, 2013 7:44 pm

Why bacteria are model investors

How bacteria invest for success
Bacteria©Tom Ferenci

Bacteria have been shown to make trade-offs between growth and risk in response to different stimuli

Some ecologists see analogies between the trade-offs that bacteria make in their survival and growth strategies and the financial decisions made by investors. Safety-first strategies – preparing to resist environmental stress – are like putting savings into cash and government bonds. High-growth strategies – multiplying as fast as possible – resemble investment in risky but potentially very profitable shares or property development.

The most powerful study so far of trade-offs has just been published by researchers from the universities of Exeter and Sydney in the journal Ecology Letters. They used a combination of mathematical modelling and lab-based synthetic biology, with bacteria genetically engineered to have different combinations of stress resistance and growth potential.

“This is the cleanest system yet that precisely defines a relationship between traded objects in a living ‘market’,” says Tom Ferenci from Sydney. “The breakthrough was in using synthetic biology to create bacteria with different investment strategies.”

The various engineered strains of E coli bacteria were exposed to four environmental challenges: cold, acid, salt and peroxide (oxidative stress) and had five nutritional resources on offer: glucose, lactate, succinate, glycerol and acetate.

Sometimes the bacteria could increase their investment in growth and multiply more rapidly without sacrificing protection against stress. Under other circumstances a small extra growth effort cost them dearly in terms of stress resistance.

After observing the trade-offs made by the engineered bacteria, the team modelled their strategies mathematically. These models were then used successfully to predict how non-engineered E coli would evolve in the lab under the same combinations of conditions.

“Combining engineered bacteria with mathematical models, we have shown that very similar investment opportunities can require different investment strategies,” says Ivana Gudelj of Exeter. “These strategies are constrained by the subtleties in trade-offs that are usually invisible or ignored in real markets.”

While the research as yet offers no clue as to how to control the likes of E coli, the authors say their study does provide the first experimental verification of the widely used “trade-off theory”, which was formulated by the US ecologist Richard Levins in the 1960s.

“This paper breaks exciting new ground in the integration of the sciences and provides compelling new evidence on resource allocation that will be of interest to multiple fields: economics, finance, business strategy and biology,” comments Dan Lovallo of the Institute for Innovation Management and Organization at the University of California, Berkeley, who was not involved in the study.

. . .

Physical basis for ‘near death experiences’

People who survive an almost fatal heart attack sometimes report vivid “near death experiences”. These include lucid visions that have been described as “realer than real”.

Believers in life after death have used near death experience as evidence for a non-corporeal basis of human consciousness, on the grounds that the dying brain could not produce such thoughts.

But experiments with rats at the University of Michigan, reported in Proceedings of the National Academy of Sciences, suggest that near death experiences – reported by about 20 per cent of cardiac arrest survivors – are grounded in science rather than something more mystical.

The researchers induced heart attacks in nine rodents while electrodes recorded brain activity. Within 30 seconds of cardiac arrest, every rat experienced a transient surge of highly synchronised neural activity, which had all the features of a very aroused brain. Almost identical patterns were recorded in the dying brains of rats during asphyxiation.

“We were surprised by the high levels of activity,” says George Mashour of Michigan. “In fact, at near death, many known electrical signatures of consciousness exceeded levels found in the waking state, suggesting that the brain is capable of well-organised electrical activity during the early stage of clinical death.”

Although the neural mechanism that triggers this heightened brain activity is not known, lead author Jimo Borjigin suggests that the reduction of oxygen or of both oxygen and glucose is responsible.

The study “provides the first scientific framework for the near-death experiences reported by many cardiac arrest survivors [and] will form the foundation for future human studies investigating mental experiences occurring in the dying brain, including seeing light during cardiac arrest,” she says.

. . .

Graphene aerogel©Haiyan Sun et al/Advanced Materials

Graphene aerogel balancing on a head of Setaria grass

World’s lightest solid unveiled in China

Scientists at Zhejiang University in China have created the world’s lightest solid, known as graphene aerogel, writes Ling Ge. Graphene, a wonder material whose inventors at Manchester University won the 2010 Nobel Prize for physics, is the thinnest possible layer of carbon – just one atom thick. Graphene aerogel consists of carbon nanotubes (tiny cylinders of carbon) coated with graphene.

It is so light that a delicate grass such as Setaria can easily bear its weight without visibly bending. A cubic centimetre weighs just 0.16mg – that is, seven times less dense than air.

To produce the graphene aerogel, the team uses a process in which solutions of carbon nanotubes and large sheets of graphene oxide are freeze-dried. The oxygen is then chemically removed, leaving a conductive carbon foam that can be morphed into any shape. The study is published in Advanced Materials.

This carbon sponge displays excellent elasticity, bouncing back when it is compressed. It can also absorb oil very rapidly, soaking up 900 times its own weight (10 times that of commercial oil absorbents).

This could open a new route to cleaning up oil spills. Due to its elasticity, the carbon sponge can be squeezed to retrieve the oil and then thrown back in the ocean to soak up more.

Other ultralight materials developed recently include “aerographite”, a lattice of carbon tubes reported by German researchers in 2012, and “metallic microlattice”, a metal foam reported by a California team in 2011.

. . .

Full-term births vary by up to five weeks

US researchers have discovered unexpected variation in the length of healthy human pregnancies, suggesting that women should not attach too much significance to their forecast “due date”.

Sweet dreams

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If you need a nightlight, make sure it’s red. According to a study at Ohio State University, blue light is worst for healthy sleep and red best, but no light at all is better still.

A full-term birth may vary naturally by as much as five weeks, according to the study in the journal Human Reproduction.

Anne Marie Jukic and colleagues at the National Institute of Environmental Health Sciences pinpointed the precise date of ovulation in 125 normal pregnancies by analysing hormonal markers in daily urine samples from women trying to become pregnant.

“We found that the average time from ovulation to birth was 268 days: 38 weeks and two days,” says Jukic. “However, even after we had excluded six preterm births, we found that the length of the pregnancies varied by as much as 37 days.”

Experts had attributed some of the apparent variation in gestation to errors in estimating the time of ovulation and implantation.

“Our measure of length of gestation does not include these sources of error, and yet there is still five weeks of variability,” she says.

On the whole, older women deliver later, with a year of age adding about a day to their pregnancy. Women who were themselves heavy babies at birth also tended to have longer pregnancies. And if a mother’s first pregnancy is longer than average, any subsequent births are likely to be late too.

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