Back in the 1990s, three scientists from West Chester University discovered a tiny brine pocket within a salt crystal in the Permian Salado Formation at the border between the US and Mexico. This pocket contained a droplet of water with trapped bacterial spores. These spores turned out to represent two bacterial species: Bacillus marismortui and Virgibacillus pantothenticus. Their isotope dating analysis indicated that these spore specimens were approximately 250 million years old. The most remarkable fact was that, when transferred to growth media, these spores could rapidly germinate and produce actively growing bacteria. Thus, these species have literally slept through the rise and fall of dinosaurs and the subsequent rise of mammals. To date, these spore samples hold the documented record of how long a living cell can remain viable in a state of dormancy.
Although some scientists have expressed skepticism about this discovery, noting that reports of ancient bacteria found in rock, coal, and Egyptian temples have not stood up to scientific scrutiny, similar findings have been made for other organisms. For instance, in one subsequent study, 100-million-year-old samples of dormant aerobic bacteria from ancient sea-floor sediments were successfully brought to life—providing another demonstration of the exceptional longevity of dormant microbial cells.
The question, however, stands regardless of any imaginable skepticism: For how long can an organism remain viable in a state of dormancy? If we find a way to protect biological molecules from damage caused by oxygen or radiation, can “simple” organisms, such as bacteria, remain viable forever?
While the answer to this question remains to be found (ironically, supported by research funded through grants that typically last about 5 years), let’s consider several documented examples of this longevity:
– A human oocyte in a female body can remain dormant but viable for over 30 years.
– A plant seed, such as that of a cucumber, retains its ability to germinate for up to 5 years—however, the oldest viable seed that has grown into a full plant was a roughly 2,000-year-old Judean date palm seed (germinated in 2005).
– Bacterial spores, like the ones mentioned above, can likely remain viable for hundreds of millions of years—a time span that greatly exceeds the age of most modern species (E. coli, for instance, are estimated to be about 20 million years old, ad we humans, for instance, are likely only about 200,000 to 300,000 years old as species).
The key question is: how do dormant cells die? What happens to the molecular structures comprising a living cell that transform a dormant cell into a dead one? And what are the major factors that catalyze this transition? Is it related to the UV radiation of genomic DNA that prevents DNA from replicating? Is it about the damage to all or a few key proteins caused by oxygen molecules? Is it about the stability of membranes? Or is it something else, perhaps exceeding our current understanding of the phenomenon of a living cell?
Perhaps some answers to these questions are written within the cells themselves—in factors that protect dormant cells from “premature” death. In all the aforementioned examples of dormancy, dormancy represents not mere inactivity but a genetically encoded program that has been evolving and reinventing itself from the very dawn of life to the present day. All these species, for instance, express special protective proteins, which include so-called hibernation factor proteins, LEA proteins, and others.
(to be continued)