Do you know those videos where people open (or even eat?) World War II military benefits? It is shocking to see how well these “foods” can be preserved after all those decades. Yuki Morono and his team of researchers from the Japan Marine Science and Technology Agency have in a way reversed this experience by providing some old organisms with modern food. However, their case involved raising ancient mud from the seabed and adding food to see if there was anything alive.
In fact, there were bacteria in the mud that probably didn’t sound surprising. But given the environment and the age of these things – 100 million years – it’s really remarkable.
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 varies greatly in terms of the types and abundance of microbial life present. In this case, however, scientists took samples of deep sediments in the middle of the South Pacific, where there are extremely few organic substances from which life can grow.
They caught sediment plugs up to about 70 meters below the seabed. Very little sediment accumulates here, so a 70-meter pile of clay represents about 100 million years of time. Sludges at the bottom of lakes or swamps often lack oxygen because the respiration of bacteria that break down organic matter consumes them. But the food here is so sparse that oxygen, nitrate and phosphate were present even in the deepest mud.
The researchers took these small plugs of sediment and injected substances that bacteria could use for growth, such as sugar and ammonia. And certainly, the bacteria grew and swallowed them – they even analyzed the isotopes of carbon and nitrogen in the individual cells to make sure they had taken up these substances. The initial amount of microbial cells was much lower than that found in more productive areas of the ocean, but they were present and viable.
The point is, scientists don’t think it’s just modern bacteria that have penetrated deep into the mud. In fact, they should not be able to move at all in that mud. The average space between the particles in the clay should be significantly smaller than the size of the bacteria. The researchers concluded that the presence of microorganisms in the oldest sediments represents communities that are about as old as the sediment itself.
DNA analysis shows slightly different combinations of bacterial types present at different depths. However, they were almost all oxygen-demanding aerobic bacteria. Some experiments did not add any more oxygen beyond what was already 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 oxygen removal, indicating that few anaerobic bacteria were present. This is in contrast to food-rich seabed sites, where anaerobic bacteria predominate.
This leads to the extraordinary statement: “Our results suggest that microbial communities widely distributed in organically poor permeable sediments consist mainly of aerobes that retain their metabolic potential under extremely low energy conditions up to 101.5. [million years]. “
There are several links in the chain that could, of course, break. If the microbes in the sediment have a certain mobility, the age comes out of the window. However, the argument against this, based on the diameter of the pores and the existence of hard, impermeable layers, is reasonable. Another possible decay is contamination, with bacteria entering the sediment sample from elsewhere. However, the team has taken several precautions here, including DNA samples taken at the time of each sample. If harmful bacteria got in during sampling, they should appear in later DNA samples, but not in the original samples – and this did not happen.
However, this does not mean that there is nothing special about the data. Cyanobacteria – photosynthetic microbes, better known as “blue-green algae” – have a look that is certainly strange given the general lack of sunlight on (and under) the seabed. A specific genus of cyanobacteria is one that thrives at least under extreme conditions. And they grew during the experiment even in the absence of light, so microbes can only have some secrets to give up.
So if scientists are right about what they have found, it is proof that life is nothing but perseverance. By slowing down their lives in extremely limited resources, these bacterial communities were able to survive an incredibly long time.
Nature Communications, 2020. DOI: 10.1038 / s41467-020-17330-1 (O DOI).