Book 2 Listening (1108796), страница 9
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But Matthew Chang, abiochemical engineer at Nanyang Technological University in Singapore, has worked out anew way to attack them. His weapon is a different type of bacterium, which he has geneticallyengineered into a finely honed anti-biofilm missile.The starting point for this new piece of biotechnology is a common gut bacterium calledEscherichia coli. Though this species is best known to the wider world for causing foodpoisoning, most strains of it are benign, and it is one of the work-horses of genetics.The story began in 2011 when Dr. Chang worked out how to program E. coli to releasedestructive antimicrobial peptides when they came into contact with another bacterium,Pseudomonas aentginosa.
This species, which is common in hospitals, likes to form biofilmsand is a frequent cause of sepsis.To deal with this film-forming propensity, Dr Chang did a second bit of genetic tinkering.He armed his modified E. coli with an enzyme called DNase I. Curiously, a lot of the chemicallinks holding individual P. aeruginosa bacteria together in a biofilm are made of DNA, amolecule more familiar as the material of genes. DNase 1 attacks DNA, and thus acts tobreak the film up.That worked too, but it was still not enough to create a useful medical agent becausethe modified E.
coli did not seek out their targets. So, as he has just reported in SyntheticBiology, Dr Chang has now done a third piece of engineering by changing his bugs' fooddetection system to react to the signalling molecules that P. aentginosa release when theyare seeking to link up with their neighbours.Laboratory tests suggest these triply armed E.
coli kill P. aernginosa biofilms six timesas effectively as the version armed only with antimicrobial peptides and DNase I. This is notyet a deployable medicine, but it is a novel and intriguing approach. And it is one that mighteasily be used against other biofilm-forming species, by changing which signaling moleculesthe engineered E. coli are sensitive to. (From The Economist.
October 12, 2013)Script 8. BioengineeringPanda poop powerMicrobes in pandas’ guts can help in biofuel productionGiant pandas are well known for being rather different from other bears. Having a dietcomposed almost entirely of bamboo is one of the things that sets them apart.
It is also whatattracted the interest of Ashli Brown of Mississippi State University, in a search for moreefficient ways to make biofuel.Most of the nutrients found in bamboo are locked away in tough substances known ascellulose and lignin. Liberating those nutrients is an energy-intensive process that involveshigh temperatures and extreme pressures when carried out in a laboratory or by an industrialprocess.Indeed, it is the cost of doing so that makes producing biofuel out of cellulose and ligninrich materials, like discarded corn (maize) cobs and husks, less financially viable thangenerating biofuel directly from more readily digestible corn kernels.
The kernels, however,can be used to feed people whereas the cobs and husks cannot. So a process that is ableeffciently to turn what is a waste product into fuel could have great potential.41Given their diet, Dr Brown knew that giant pandas had to have legions of microbes intheir gut that were strong enough to break cellulose and lignin down. If it was possible toidentify those microbes and find the enzymes within them they might be used to improvebiofuel production.So, Dr Brown and her colleagues got to work analysing piles of panda faeces for thepresence of RNA strands belonging to the microbes. The team then searched throughmicrobial databases to identify the genre that these microbes belonged to and determinewhich known species they were most closely related to.
This identification process allowed DrBrown to run a comparative analysis that teased out minor differences between the microbesto reveal which ones carried the traits that made them particularly adept at breaking down thebamboo material.This produced 17 microbes with the ability to digest cellulose and six that looked likegood candidates for digesting lignin. The microbes were then tested in the laboratory. Theywere found to be capable of breaking down 65.4% of the tough materials they were givenand transforming much of them into the sorts of energy-rich sugars that are readily fermentedinto bioethanol or biodiesel, Dr Brown told a national meeting of the American ChemicalSociety in Indiana this week.Considering that most cellulose- and lignin-based materials end up as compost, orworse, in landfills, the ability to convert such a large percentage of them into potential biofuelproducts is encouraging.
Dr Brown, though, is quick to point out that optimising theperformance of the enzymes employed by the microbes so that they can be usedcommercially is going to be a long and hard job. But thanks to the giant panda being savedfrom extinction, it is one that could be well worth the effort. (From The Economist, September14, 2013)42Unit 5. Domesticated animalsScript 9. Canine evolutionThe company of wolvesFoxes can be tamed deliberately, by selective breeding.
But this probably recapitulatesa process that happened accidentally, many millennia ago, to wolves. The product of thatwas the animal now known as the dog. But where on Earth this happened is moot. Fossilshave been used to make the claim for places as diverse as Russia and the Middle East.Genetic evidence has pointed towards East Asia, with some people believing that NewGuinea singing dogs and their Australian offshoots, dingoes, are largely unchangeddescendants of the first pooches.Olaf Thalmann of the University of Turku, in Finland, Robert Wayne of the University ofCalifornia, Los Angeles, and their colleagues beg to differ. They think Fido was born inEurope, and that they have the DNA to prove it.The DNA in question is from mitochondria: cellular power packs that have their owngenes.
Because each cell has lots of mitochondria, but only one nucleus, there is a betterchance of getting mitochondrial genes than nuclear genes from a fossil. And that, as theydescribe in Science, is what Dr Thalmann, Dr Wayne and the rest of the team did.They extracted mitochondrial DNA from 18 fossil canids, making sure to include theearliest doglike creatures that show skeletal signs of domestication.
(These date from36,000-15,000 years ago.) They then compared what they found with DNA from 49 modernwolves collected from all over the northern hemisphere, and also with that from 77 moderndogs.Modern dogs, they knew from previous studies and confirmed with this one, belong tofour genetic groups different branches of the canine family tree, in other words.
Several fossilcanids from Europe, the researchers found, also belong to one or other of these groups, asdo the continent’s modern wolves. Middle Eastern and Asian wolves, both ancient andmodern, are, by contrast, not members of any of these groups and cannot therefore beclosely related to modern dogs.Three dog fossils from the Americas, dating back between 1,000 and 8,500 years, alsoshared their ancestry with modern mutts. Presumably their forebears accompanied the firstAmerican colonists 15,000 years ago when they crossed the Bering land bridge that linkedthe New and Old Worlds before the sea level rose to flood it at the end of the last ice age.Dogs’ division into four groups means one of two things.
Either domestication happenedmore than once, or each group is descended from post-domestication crosses between dogsand wolves that brought new mitochondrial DNA into the line. Regardless of which is true,this study seems both to pinpoint where dogs come from and to confirm that theirdomestication predates the invention of agriculture, about 10,000 years ago.For reasons yet unknown, wolves and humans first got together when people stillhunted and gathered for a living. Perhaps their similar ways of life both species then dwellingin small, mobile bands allowed the two to collaborate in hunting or defence. Or perhaps theyjust enjoyed each other’s company. Rather like today, in other words.
(From The Economist,November 16, 2013)Script 10. Fish farmingHigh-tech breedersYou do not have to use genetic engineering to benefit from geneticsThe japanese are great guzzlers of fish, but fish are in finite supply. And farming them toincrease that supply can be tricky, because many species are susceptible to disease whencrowded together.43That fact is the impetus behind a study led by Takashi Sakamoto of the TokyoUniversity of Marine Science and Technology. Dr Sakamoto is using a combination ofmodern genetic techniques and classical breeding to produce fish that can survive crowdingwithout falling ill.His first task was to establish genetic maps for each of the species involved - flounders,trout and amberjack.
Such a map is not a complete DNA sequence, which would beunnecessarily detailed, but rather a set of signposts, using which a geneticist can navigatehis way around an animal's chromosomes. The signposts are places where DNA routinelydiffers within a species from one individual to another, and does so in characteristic ways.When sperm and eggs form, blocks of DNA from a creature's mother and father are swappedaround, taking the signposts with them.
If you have enough signposts it is possible to followthese blocks through the generations.Dr Sakamoto now has genetic maps for hundreds of individual fish, and he also hasdata, collected in collaboration with Japan's three main fishery-research institutes, on howwell these fish did when faced with plague or pestilence. He has thus been able to tease outwhich versions of which signposts are associated with rude health.It is not the signposts themselves which confer protection from disease. That is done bynearby genes.
However, gene and signpost travel together from parent to offspring, so thepresence of the one can be inferred from the presence of the other. And that gives DrSakamoto an invaluable head-start when it comes to breeding disease-resistant fish. He isable to see how many resistance genes have ended up in each animal and then pick themost resistant to breed from. He thus gains much of the advantage that might come fromactual genetic engineering (ie, directly transplanting resistance genes into fish eggs) withouthaving to do the engineering itself. It also means he can breed healthier fish withoutnecessarily knowing what the health-giving genes are - though it would obviously be a bonusto have such knowledge, and he is indeed busy searching the DNA near the relevantsignposts to find the truth.Dr Sakamoto's research group has already managed to produce flounders which areresistant to virallymphocystis (a serious problem on flounder farms) and these are now in theshops.
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