Digest Of The. Economist. 2006(6-7)
A wealth of genetic information is to be found in the human gut
BACTERIA, like people, can be divided into friend and foe. Inspired by evidence that the friendly sort may help with a range of ailments, many people consume bacteria in the form of yogurts and dietary supplements. Such a smattering of artificial additions, however, represents but a drop in the ocean. There are at least 800 types of bacteria living in the human gut. And research by Steven Gill of the Institute for Genomic Research in Rockville, Maryland, and his colleagues, published in this week's Science, suggests that the collective genome of these organisms is so large that it contains 100 times as many genes as the human genome itself.
Dr Gill and his team were able to come to this conclusion by extracting bacterial DNA from t
醇醚燃料he faeces of two volunteers. Because of the complexity of the samples, they were not able to reconstruct the entire genomes of each of the gut bacteria, just the individual genes. But that allowed them to make an estimate of numbers.
What all these bacteria are doing is tricky to identify—the bacteria themselves are difficult to cultivate. So the researchers guessed at what they might be up to by comparing the genes they discovered with published databases of genes whose functions are already known.
This comparison helped Dr Gill identify for the first time the probable enzymatic processes by which bacteria help humans to digest the complex carbohydrates in plants. The bacteria also contain a plentiful supply of genes involved in the synthesis of chemicals essential to human life—including two B vitamins and certain essential amino acids—although the team merely showed that these metabolic pathways exist rather than proving that they are used. Nevertheless, the pathways they found leave humans looking more like ruminants: animals such as goats and sheep that use bacteria to break down otherwise indigestible matter in the plants they eat.
The broader conclusion Dr Gill draws is that people are superorganisms whose metabolism represents an amalgamation of human and microbial attributes. The notion of a superorganism has emerged before, as researchers in other fields have come to view humans as having a diverse internal ecosystem. This, suggest some, will be crucial to the success of personalised medicine, as different people will have different responses to drugs, depending on their microbial flora. Accordingly, the next step, says Dr Gill, is to see how microbial populations vary between people of different ages, backgrounds and diets.
Another area of research is the process by which these helpful bacteria first colonise the digestive tract. Babies acquire their gut flora as they pass down the birth canal and take a gene-filled gulp of their mother's vaginal and faecal flora. It might not be the most delicious of first meals, but it could well be an important one.
Zapping the blues
The rebirth of electric-shock treatment
财智老板通
ELECTRICITY has long been used to treat medical disorders. As early as the second century AD, Galen, a Greek physician, recommended the use of electric eels for treating headaches and facial pain. In the 1930s Ugo Cerletti and Lucio Bini, two Italian psychiatrists, used electroconvulsive therapy to treat schizophrenia. These days, such rigorous techniques are practised less widely. But researchers are still investigating how a gentler electric therapy appears to treat depression.
Vagus-nerve stimulation, to give it its proper name, was originally developed to treat severe epilepsy. It requires a pacemaker-like device to be implanted in a patient's chest and wires from it threaded up to the vagus nerve on the left side of his neck. In the normal course of events, this provides an electrical pulse to the vagus nerve for 30 seconds every five minutes.
This treatment does not always work, but in some cases where it failed (the number of epileptic seizures experienced by a patient remaining the same), that patient nevertheless reported feeling much better after receiving the implant. This secondary effe
ct led to trials for treating depression and, in 2005, America's Food and Drug Administration approved the therapy for depression that fails to respond to all conventional treatments, including drugs and psychotherapy. pamam
Not only does the treatment work, but its effects appear to be long lasting. A study led by Charles Conway of Saint Louis University in Missouri, and presented to a recent meeting of the American Psychiatric Association, has found that 70% of patients who are better after one year stay better after two years as well.
The technique builds on a procedure called deep-brain stimulation, in which electrodes are implanted deep into the white matter of patients' brains and used to “reboot” faulty neural circuitry. Such an operation is a big undertaking, requiring a full day of surgery and carrying a risk of the patient suffering a stroke. Only a small number of people have been treated this way. In contrast, the device that stimulates the vagus nerve can be implanted in 45 minutes without a stay in hospital.
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