Gut-Level Census Surprises

Scientists have discovered a trove of life-forms lurking in the human gut -- 395 different bacteria, 60% of which had never been described, according to a report published Thursday in the online edition of the journal Science.

The study analyzed samples of stool and mucous from six parts of people’s colons. The results were surprising and “a bit sobering,” said the paper’s lead author, Stanford University researcher Dr. Paul Eckburg.

Eckburg and his team used DNA analysis to identify the bacteria in samples harvested from three middle-aged Canadians during colonoscopy examinations.

About 80% of the bacteria had never been cultured in a laboratory, probably because they need the oxygen-free conditions of the gut to grow.

The scientists also found that the species of bacteria varied from one gut to the next, perhaps because of dietary differences or because people are exposed to different microbes when their guts -- sterile at birth -- are first colonized.

Most of the bacteria belong to two groups known as Firmicutes and Bacteroidetes. Some of the bacteria are thought to feed the gut wall, stimulate the growth of nutrient-supplying blood vessels and prevent disease-causing germs from taking up residence in the colon.

Samples from more than 300 people remain to be analyzed, so the census may be far from complete, Eckburg said.

“You can think of it as the tip of the iceberg,” he said.

The findings are part of a larger study, which is seeking links between microbes in the gut and bowel disorders such as Crohn’s disease and ulcerative colitis.