Researchers revive bacteria from the era of the dinosaurs The bugs that time forgot
FAR FROM the life-sustaining light of the sun, the deep sea floor appears barren and desolate. Its appearance, however, belies a thriving bacterial ecosystem that may contain as much as 45% of the world’s biomass of microbes. This ecosystem is fuelled by what is known as marine snow—a steady shower of small, nutrient-rich particles that fall like manna from the ocean layers near the surface, where photosynthesis takes place.
Not all of the snow is digestible, though. And the indigestible parts build up, layer upon layer, burying as they do so the bugs in the layer below. To look at how well these bacteria survive entombment a group of researchers led by Morono Yuki of the Japan Agency for Marine- Earth Science and Technology and Steven D’hondt of the University of Rhode Island studied samples collected in 2010 by the Integrated Ocean Drilling Programme, a decade-long international expedition of which they were part. Their results, just published in Nature Communications, are extraordinary. They seem to have brought back to life bacteria that have been dormant for over 100m years.
For many microbes, burial is an immediate death sentence. Some, however, are able to enter a state of dormancy—slowing their metabolisms down almost, but not quite, to zero. They can remain in this state for considerable periods. But precisely how long has been a subject of debate.
The samples Dr Morono and Dr D’hondt chose for examination came from a place in the Pacific Ocean where the sea bed is nearly 6,000 metres below the surface. That made drilling a challenge. But the expedition was able to recover sediment cores stretching all the way down to the underlying rock— a thickness of 100 metres in some cases. The oldest material in these cores dated back 101.5m years, to the middle of the Cretaceous period, the heyday, on land, of the dinosaurs.
Examination of the sediments showed that even the oldest still contained a few bacteria. The question was, were these organisms dead or alive? To find out, the researchers incubated the samples, slowly feeding them compounds rich in carbon and nitrogen in order to coax any still-living microbes out of their dormancy.
The results shocked Dr Morono, “At first I was sceptical, but we found that up to 99.1% of the microbes in sediment deposited 101.5m years ago were still alive.” And there was quite a variety of them, too. The team found representatives of phyla called Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria, all of which are familiar to microbiologists. In one sample (admittedly from a mere 13.5m years ago) they also discovered representatives of the archaea, a group of organisms that resemble bacteria under a microscope, but have a biochemistry so different that they are regarded as a separate domain of life.
Cretaceous Park
To find such living fossils from as far back as the Cretaceous is extraordinary. It is not possible to be sure, given the length of time involved, that they have undergone no growth and cell division whatsoever. But if they have, it will have been minimal given the lack of nutrients in the ooze they were found in. Nor is it likely that they migrated there from layers above. The ooze in question was sealed off by a bacteria-proof layer of chertlike material called porcellanite. measures. On July 27th Antwerp, Belgium’s most populous province, announced a night curfew for nonessential movement and made masks mandatory in public spaces; people were told to stay at home as much as possible. Covid clusters have emerged across Germany, in care homes, workplaces and private parties, forcing officials to impose localised lockdowns. In mid-july the Catalan authorities reimposed a strict lockdown in Lleida, a city of 140,000. Nightclubs in Barcelona and other hotspots in Spain were recently shut or ordered to close early.
Varying covid-19 rates across Europe have prompted countries to make some tough choices. In a normal year, some 18m Britons seek fun in the sun in Spain, along with lots of other northern Europeans. But as cases in Spain notched up, Britain and Norway swiftly brought back quarantine for people coming from Spain. Vacationers to Greece from some Balkan countries must now show proof of a negative covid-19 test to enter the country. That has dealt a blow to whatever remained of the foreign tourist season in much of southern Europe. But there has been a collective sigh of relief among health officials watching with trepidation clubs and beaches crowded with drunk foreigners.
That, however, still leaves the matter of intensifying local transmission. A pattern that cuts across Europe is that new cases have been mostly among people in their 20s and 30s; clusters linked to large parties have become a recurring theme across the continent. German politicians have warned that citizens are growing complacent about the dangers; surveys confirm suspicions that fewer people are avoiding crowded public spaces or private gatherings. Dr Kluge says that the priority in Europe now is to ensure that young people comply more with such precautions. If that fails, he says, it won’t be long before infections spread to older, vulnerable people.