Biochemist Shigeru Deguchi is exploring the limits of life by giving bacteria rides on a laboratory centrifuge, a tabletop merry-go-round that can touch a top speed of 65,500 revolutions per minute (rpm).

Since the 1970s, scientists have found bacteria thriving in some of the most hostile places on earth — from boiling hot volcanic vents to frigid Antarctic ice to lakes with salts and acids — revealing a capacity to tolerate extreme environments.

Deguchi, a biochemist at the Institute of Biogeosciences in Yokosuka, Japan, has now shown that some bacteria, including one that is found in the human gut, can live and reproduce in extreme gravitational fields — up to 4,03,627 times the gravity experienced on earth. His findings suggest that the high gravity of giant planets detected outside the solar system need not be a limiting factor for at least microbial life.

“We can elucidate the limits of life by studying microbes in extreme environments. This knowledge is critical in assessing the probability of life in extraterrestrial environments — it helps us narrow down possible targets to search,” Deguchi told Knowhow. Deguchi and his colleagues have described their observations of microbes in hypergravity in the journal Proceedings of the National Academy of Sciences.

But bacteria that can survive extreme environments — also called extremophiles — aren’t just scientific curiosities. Laboratory experiments indicate that housekeeping enzymes produced by some extremophiles may have real world applications.

Five years ago, chemist Mala Rao and her colleagues at the National Chemical Laboratory (NCL), Pune, showed that a bacteria picked up from Barabanki in Uttar Pradesh that survives alkaline environments can help in the biopolishing of denims — a potential boon for the textile industry. Another alkali-loving bacteria isolated from a hot spring in Vajreshwari, a tourist site in Maharashtra, has been shown by the NCL researchers to be useful in the pulp and paper industry. About a decade ago, defence researchers developed a cocktail of waste-digesting bacteria that could function in extreme cold — to tackle human waste in Siachen. The waste-digesters were even pitched to Indian Railways as a way to avoid dropping human waste on tracks.

“Extremophiles show promise for applications in industry and research,” Rao told Knowhow. “But the economics of using them on an industrial scale has yet to be worked out.”

Before Deguchi began his experiments, there had been little research on how microbes respond to extreme gravity. Most studies on gravity had involved the study of microbes ferried into outer space — where gravitational forces are weaker. A study of the bacteria, E.coli, for instance, in the 1990s had shown that the duration of growth and their final count doubled during space flights. Another study suggested that the production of antibiotics by some bacteria is suppressed in microgravity.

The only documented studies that had exposed E.coli to extreme gravity in the 1960s suggested that the bacteria showed typical growth patterns at 1,000g, 1,000 times the gravity on earth, but displayed disturbed growth at 1,00,000g.

Deguchi and his colleagues picked several microorganisms for their experiments. The microorganisms were suspended in vials with a broth of nutrients and spun around in a centrifuge — the speed increased to reach 65,500 rpm, equivalent to 4,03,627g.

The researchers studied the three obvious effects of hypergravity — sedimentation of cells, a condition in which the cells clump together to form pellets, mechanical deformation, and the effects of pressure. They found that all microorganisms they studied displayed normal growth up to 20,000g, but two species — E.coli, and Paracoccus denitrificans — continued to proliferate even at 4,03,627g.

Shigeru Deguchi

Scientists believe a primitive class of microorganisms classified as prokaryotes can alone tolerate hypergravity environments. Eukaryotes — all other small and large organisms on earth — have internal structures such as nuclei and mitochondria in their cells. These tend to sediment easily, while prokaryotic cells which do not possess such tiny organelles are less vulnerable to sedimentation.

But why some prokaryotes survive 4,00,000g and others didn’t is still unclear.

“These findings open new real estate in the quest to locate habitable environments beyond our solar system,” said Jack Farmer, an astrobiologist at the Arizona State University, who was not connected with the study. “They provide important context information for the rapidly expanding field of extrasolar planet research and the growing inventory of potentially habitable extrasolar planets,” Farmer told Knowhow.

Most extrasolar planets discovered so far have masses much larger than Jupiter, with gravitational fields a lot stronger than Earth’s. While traditional strategies to look for potentially habitable environments have emphasised the search for basic requirements such as liquid water, nutrient and energy sources, Farmer said, the effects of high gravity on the viability of simple living systems has not been studied until now.

Deguchi points out that hypergravity microbes may also have practical applications. The suppression of antibiotics production by microbes observed in microgravity environments may be enhanced in high gravity environments.

Hypergravity could then be a route to higher efficiency in antibiotic production.