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Tiny BubblesOldest evidence yet formethane makers

Analyses of the gases dissolved in watertrapped in ancient minerals suggest thatmethane-generating microbes have beenaround almost 3.5 billionyears, more than 700 mil-lion years longer than pre-vious geologic evidencehad indicated. Becausemethane prevents the lossof heat from Earth, thegas generated by thosemicrobes could explainhow the planet kept warmduring the Archaean eraeven though the sun thenproduced less than three-fourths the radiation thatit does today.

Methane is a minorconstituent of Earth’satmosphere, today mak-ing up only about 1.8parts per million of air.There are three majorsources of atmosphericmethane: some types ofmicrobes that live in oxy-gen-poor environments,the heat-induced degradation of organicmatter trapped in sediments, and the chem-ical reactions of simple inorganic compoundssuch as carbon dioxide and hydrogen.

Although methane produced via onemethod is chemically indistinguishablefrom that produced by the others, theratio of carbon isotopes found in a sam-ple of methane provides a clue to itssource, says Yuichiro Ueno, a geochemistat the Tokyo Institute of Technology inYokohama, Japan. Methane from biolog-ical sources contains less carbon-13 thandoes methane from nonbiological sources.

Ueno and his colleagues analyzed sam-ples of transparent quartz taken from theDresser formation in Western Australia.Radioactive dating of those samples, as wellas of the volcanic layer deposited directlyatop them, suggests that the Dresser quartz

formed between 3.49 billion and 3.46 billionyears ago, says Ueno. When the quartz crys-tallized, it trapped tiny droplets of water.

Spectral analyses revealed minusculeamounts of methane dissolved in thosedroplets. The researchers then ground upsmall samples of fluid-bearing quartz andanalyzed the methane that was released.

Because the escaping methane con-tained much less carbon-13 than is nor-mally found in atmospheric methane, thecarbon in the gas probably had a biologicorigin, say the researchers. The dearth ofpropane and other long-chain hydrocar-bon gases coming from the droplets indi-cates that the methane didn’t derive fromthe thermal degradation of organic mat-ter. Therefore, the researchers propose inthe March 23 Nature that the methanetrapped in the quartz must have been pro-duced by microbes.

Ueno and his colleagues “have probablyuncovered the oldest-known samples of bio-

logically produced gas,”says Don E. Canfield, abiogeochemist at theUniversity of SouthernDenmark in Odense.

“It’s wonderful newsif they’ve measured apreserved sample [ofmethane],” says James F.Kasting, a geochemist atPennsylvania State Uni-versity in University Park.Most theories aboutEarth’s early atmospherepresume concentrationsof methane more than500 times as great asthose in today’s atmos-phere, he notes.

Previous studies hadidentified microorgan-isms that used sulfateto fuel their metabo-lism 3.5 billion yearsago, but those microbes

produced no methane. The new researchadds a methane producer to the mix ofmicrobes known to be active then, saysCanfield. —S. PERKINS

Mood Meds’Second WindDepression drugs aided byextra treatment step

A second, modified course of drug treat-ment fosters recovery in a substantialminority of depressed adults who don’t feelbetter after treatment with a commonlyprescribed antidepressant, according to afederally funded investigation.

Among depressed patients who didn’timprove on the antidepressant citalopram(Celexa), one in four became virtually symp-tomfree by switching from citalopram to asecond antidepressant. In another test, onein three patients improved comparablywithin 14 weeks of adding another antide-pressant to their citalopram regimen.

The researchers had earlier reported thatabout a third of patients get relief fromcitalopram alone. With the effect of the sup-plemental drugs, about half of the 4,041depressed patients participating in the proj-ect shed most or all of their symptoms.

“A 50 percent remission rate is extraor-dinarily good given major depression’schronic nature,” says psychiatrist A. JohnRush of the University of Texas South-western Medical Center at Dallas, directorof the Sequenced Treatment Alternativesto Relieve Depression (STAR*D) trial.

The researchers studied outpatients withmajor depression at 41 U.S. psychiatric andprimary care facilities. Participants initiallyreceived citalopram for an average of 47 days. The drug increases serotonin activ-ity in the brain. About 30 percent of peopledisplayed symptom remission, Rush’s groupreports in the January American Journal ofPsychiatry. Results for still-depressedpatients who chose a second treatmentappear in two reports in the March 23 NewEngland Journal of Medicine.

A team led by Rush studied 727 patientswho switched medications. Each volunteerwas randomly assigned to receive either ser-traline, another serotonin-enhancing drug;bupropion, a dopamine-and-norepineph-rine booster; or venlafaxine, which raisesavailability of serotonin and norepineph-rine to brain cells. Each medication yieldedremission in 25 percent of patients.

A group led by University of Texas psy-chiatrist Madhukar H. Trivedi studied 565patients who continued taking citalopramalong with either bupropion or the sero-tonin-enhancing drug buspirone. In eachgroup, 33 percent of the patients becamesymptomfree.

Another 369 patients opted for a formof psychotherapy called cognitive therapy,either alone or with medications. Theresults of those treatments will be pub-lished later this year. In other studies, cog-nitive therapy has worked as well as anti-depressants as a primary treatment (SN:11/5/05, p. 299).

Certain genetic traits may identify indi-viduals likely to benefit from specific anti-depressants, Trivedi says. A genetic analy-sis of 1,953 STAR*D patients, slated toappear in the May American Journal ofHuman Genetics, shows that many peoplewho responded well to the initial treatmentwith citalopram possess a specific versionof a gene critical to serotonin transmission.

The new findings are “illuminating anddisconcerting,” says psychiatrist David R.

GAS FROM ROCK Microbesprobably produced the methanedetected in micrometer-size dropletsof water trapped within these grainsof quartz (colored by polarized light).

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