You know those videos where people open (or even eat?) World War II rations? It is shocking to see how well these “foods” can be preserved after all these decades. Somehow, Yuki Morono and his team of researchers from the Japan Science and Technology Agency for the Sea and Earth transfer this experience by giving modern food to some old organisms. But their case involved removing ancient mud from the seabed and adding some food to see if anything was alive there.
In fact, there were bacteria in the mud, which probably doesn’t sound surprising. But given the environment and the age of these things – 100 million years – that’s actually quite remarkable.
In the deep
Life deep underground or under the seabed is not studied, nor is the easily accessible surface world. Sampling has shown that seabed mud in different parts of the ocean differs greatly in species and abundance of microbial life. But in this case, the researchers took samples of deep sediments in the middle of the South Pacific, where there is very little organic matter for life to grow.
They grabbed sediment plugs up to about 70 meters below the seabed. Very little sediment accumulates here, so a pile of clay 70 meters thick is about 100 million years old. The mud at the bottom of lakes or swamps often lacks oxygen, as the respiration of bacteria that break down organic matter consumes everything. But food is so scarce that oxygen, nitrates and phosphate are present in even the deepest mud.
The researchers took these small stoppers from sludge and injected substances that bacteria can use for growth, such as sugar and ammonia. And bacteria certainly grow and absorb them – they even analyze isotopes of carbon and nitrogen in individual cells to see if they have ingested these substances. The initial abundance of microbial cells was far lower than found in more productive areas of the ocean, but they were available and viable.
The thing is, researchers don’t think it’s just modern bacteria that have dug deep into the mud. In fact, they should not be able to move at all in this mud The average space between the particles in the clay should be significantly less than the size of the bacterium. The presence of microbes in the oldest sediments are communities that are almost as old as the sediments themselves, the researchers concluded.
DNA analysis shows slightly different combinations of bacterial species present at different depths. However, almost all of them consumed oxygen aerobic bacteria. Some experiments did not add extra oxygen beyond what was already present in the mud, and the bacterial activity from the added food quickly consumed all the oxygen. In these experiments, there was very little growth after the disappearance of oxygen, suggesting that there were few anaerobic bacteria. This is in contrast to sea-rich food-rich areas where anaerobic bacteria predominate.
This leads to a remarkable statement: “Our results suggest that microbial communities, widespread in low-organic additives, consist mainly of aerobes, which retain their metabolic potential under extremely low-energy conditions up to 101.5 [million years]. “
There are several links in the chain where this can obviously go wrong. If the microbes have some mobility in the sediment, the eyelids go out the window. But the argument against this, based on the diameter of the pores and the space of hard, impermeable layers, is reasonable. The other potential stone is contamination, as bacteria enter the sludge sample from elsewhere. But the team took a number of precautions here, including DNA samples taken during the collection of each sample. If ungodly bacteria are found during sampling, they should appear in later DNA samples, but not in the original – and this has not happened.
This does not mean that there is nothing special in the data. Cyanobacteria – photosynthetic microbes, better known as “blue-green algae” – create a species that is certainly strange given the complete lack of sunlight on (and under) the seabed. The specific genus of cyanobacteria is the one that grows at least in extreme conditions. And their growth during the experiment also occurred in the absence of light, so the microbes may simply have some secrets to give up.
So if researchers are right about what they’ve found, it’s evidence that life is nothing, if not permanent. By delaying living in extremely limited means, these bacterial communities may have survived for just an incredible amount of time.
Nature Communications, 2020. DOI: 10.1038 / s41467-020-17330-1 (Regarding DOI).