Yeast genes conspire to produce more biofuel
Researchers at MIT have engineered a new strain of yeast that can pump out ethanol with increased efficiency. Applying their findings to industrial yeast strains could help overcome some of the problems in the production of biofuels from corn and other plant materials, and help increase the supply of these alternative fuels.
Ethanol, which is most often mixed with gasoline for use in vehicles, is produced in large bioreactors by yeast that ferment plant sugars. But high initial glucose concentrations and later high ethanol levels inhibit the growth of the organisms. Attempts to create strains resistant to these harsh conditions by modifying one gene at a time has not worked, so postdoctoral researcher Hal Alper, who works in the lab of chemical engineering professor Gregory Stephanopoulos, decided to take a more expansive approach: altering many genes at once. To do this, he introduced multiple random mutations into a gene coding for a protein that regulates many genes in the yeast Saccharomyces cerevisiae.
The approach paid off. By generating a large number of yeast with mutated versions of a global gene regulator, called the TATA-binding protein, and growing the yeast in high glucose and ethanol, the researchers found a winner. The top performing strain proved able to withstand ethanol concentrations of 20 percent (the parent strain failed to grow in 6 percent ethanol). And the strain pumped out 50 percent more ethanol per hour than the original yeast.
This high performance was the result of complex reprogramming of the yeast genome, involving changes in the activity of hundreds of genes. The researchers identified the three key mutations in the TATA-binding protein gene required to soup up the organism.
The researchers say that, in theory, this technique could be applied to other organisms to generate optimized strains for a variety of industrial and medical uses.
The work appears today in Science. Pat McCaffrey
Environment trumps genes in young mice with learning problems
Providing laboratory mice with deluxe accommodations—more space and a chance to exercise and play with toys—helps them overcome a genetic defect that affects the ability of mice raised in a standard lab environment to learn and remember.
The results, from Tufts University Medical School researcher Larry Feig, show that mice in the enriched environment use additional biochemical pathways to achieve the neuronal changes necessary for learning and memory formation. This flexibility has not been observed in conventionally housed mice.
There’s no question that environmental enrichment or deprivation alters brain development, but exactly what happens in the brain during this process has not been well understood.
Feig and his collaborator, Dean Hartley of Harvard Medical School, had previously found that mice raised in conventional cages and lacking certain proteins called Ras-GRF, which are involved in key biochemical pathways, have defects in their ability to strengthen the connections between certain neurons in response to stimulation, a necessary process for learning and memory formation.
In the new study, the researchers placed these mice in more-spacious cages with toys for six hours a day over a two-week period. By studying slices of the mice’s brains, they found that those defects had disappeared. With further probing, they revealed that the mice activated an additional signaling pathway to compensate for the missing Ras-GRF proteins.
They also found that animals that were deprived early in life but placed in the enriched environment as adults could not overcome the lack of the Ras-GRF proteins.
The researchers speculate that their findings could be relevant to people, suggesting how optimal environments for infants and young children might maximize the ability for the brain to compensate for genetic weaknesses.
The paper appeared this week in Current Biology. Pat McCaffrey
How to cool quantum computers
As computers run faster, they run hotter, calling for ever-more-powerful cooling mechanisms. In today’s issue of Science, researchers led by Sergio Valenzuela of MIT reveal tricks of quantum physics that could give quantum computers their first direct cooling mechanism.
Quantum computers exploit properties of quantum physics to run many more operations in parallel than current computers, theoretically increasing computing speeds. So far, though, only simple prototypes exist, capable of small feats like multiplying 3 by 5.
Researchers are hard at work on the basic computing elements of these computers, called quantum bits or qubits. Unlike traditional computer bits, which exist in one of two states—either 0 or 1—qubits can be in two or more states. Qubits can inadvertently switch states due to heat, light, and other disturbances, so keeping them cool is important for the development of quantum computing. So far, the only method of cooling qubits has been to keep them immersed in liquid helium.
Now the MIT researchers have demonstrated a new way of cooling qubits directly. They used a 10-micrometer wide loop of niobium, a superconducting material, as a qubit and ran an electric current through the loop. In its lowest quantum energy state, the current circulated only in one direction, clockwise. But inevitably the material absorbed some heat from its surroundings; in this more energetic state, part of the current began circulating counter-clockwise.
To cool the qubit back down, Valenzuela and colleagues used a method that seems paradoxical: they shot the qubit with a microwave photon. At a specific frequency, the photon boosted the already-excited current to an even higher energy state. This energized current flowed clockwise, just as in the lowest state. Because of the properties of these energy states, this energized current could much more easily “decay” back to its lowest energy state. In the process, the qubit shot out a photon—one more energetic than the photon it originally absorbed. This way, it cooled down to a chilly three millikelvin.
The researchers say this cooling method could work for most other kinds of qubits built from a solid material. And they say it could be useful in a practical quantum computer; one use would be to “reset” qubits to their lowest energy state between calculations, which would also keep them cool. Mason Inman
