For a few species of microbe, DNA is more than a library of genetic information: it鈥檚 also lunch. Some聽bacteria聽that live in the mud below the seafloor聽appear to survive by eating DNA trapped in the dirt.
鈥淭his is one of the yummiest things to eat down there,鈥� says Gustavo Ram铆rez at the University of Southern California. 鈥淚t鈥檚 got the major macronutrients that you get in your lawn fertiliser 鈥� carbon, nitrogen and phosphorus.鈥�
Biologists have already established that 鈥� molecules no longer locked away inside biological cells. But the fact that this 鈥榚xtracellular鈥� DNA suggests it must be recycled, says Kenneth Wasmund at the University of Vienna, Austria. That could be because some of the bacteria living in the mud break it down and reuse its components, he says.
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To find out, Wasmund and his colleagues collected samples of mud from the bottom of Baffin Bay in the North Atlantic Ocean. Back in the lab, they placed the mud samples in anaerobic conditions at 4掳C 鈥� replicating conditions seen in the聽mud at the bottom of Baffin Bay.
DNA-eaters identified鈥�
鈥淲e incubated them for a few weeks to let the microbes do their thing,鈥� says Wasmund. Then they used lab equipment to separate out microbes that had broken down the DNA and incorporated it into their cells. Finally, the researchers used genetic sequencing techniques to identify these DNA-eating microbes and reconstruct their genomes.
The team found five different types of bacteria dined on the DNA. Four of the five seemed to be opportunistic DNA consumers, just taking advantage of the molecule because it was available.
But the fifth became particularly abundant after Wasmund and his colleagues added DNA to the mud, suggesting it might be a specialist DNA-eater. What鈥檚 more, its genome shows it produces several different enzymes specifically for聽breaking down key components of the extracellular DNA.
鈥nd named
The team named the DNA-eating specialist Candidatus Izemoplasma acidinucleici, a reference to its taste for DNA, which stands for deoxyribonucleic acid.
They say their findings have yet to be peer-reviewed, but an聽independent study聽 鈥� this time in the English Channel 鈥� and was published a few months ago.
Ram铆rez says he is impressed it was possible to identify specific microbes that eat the DNA, although he points out that these bacteria might behave differently in the seafloor because Wasmund and his colleagues didn鈥檛 perfectly replicate the extreme conditions in those environments, such as the extremely high pressure.
He also thinks we should consider the possibility that some of the microbes do more than simply break down and eat the DNA they find. 鈥淭here is potential for it to be used as genetic information rather than food,鈥� he says. Some of the mud at the bottom of the ocean contains so little food that microbial populations living there might struggle to find the energy to go through cell division and, ultimately, to evolve.
鈥淏ut there could be entire genes sitting in the sediment,鈥� he says. 鈥淐ells could potentially pick them up and change their genetic makeup 鈥� and therefore evolve without the need for reproduction.鈥�
BioRxiv
