Bacterial cells are far simpler than animal cells - bacterial cells don't even have membrane-bound organelles like mitochondria or a nucleus. But a new study has suggested that bacterial cells are able to form something like a memory when it comes to the orchestrated behavior or function of microbes, like what might be seen in some infections or antibiotic resistance. This study found that iron can work like a chemical signal that is used by bacteria to generate and pass down memories over multiple generations. The findings, which used non-pathogenic E. coli cells, have been reported in the Proceedings of the National Academy of Sciences (PNAS).
Previous studies have shown that bacteria can move as one, in a kind of swarm, and that subsequent swarms have better performance. Since bacterial cells are nothing like neurons or nervous systems, scientists wanted to know how they collectively improved.
"Bacteria don't have brains, but they can gather information from their environment, and if they have encountered that environment frequently, they can store that information and quickly access it later for their benefit," said lead study author Souvik Bhattacharyya of the Department of Molecular Biosciences at The University of Texas at Austin.
The researchers found that iron levels can allow the bacteria to form memories, sort of like a computer does. Iron is one of the most plentiful elements on the planet, and it is commonly found in bacterial cells. When iron levels are lower, the swarming function, in which the bacteria's flagella propels them around, is better. But bacterial cells in places like sticky biofilms that often stay in place have higher iron levels. In bacteria that are antibiotic resistant, iron levels are neither low nor high. The researchers found that these characteristic levels remained the same in bacterial cells and their progeny for at least four generations. By seven generations, they disappeared.
"Before there was oxygen in the Earth's atmosphere, early cellular life was utilizing iron for a lot of cellular processes. Iron is not only critical in the origin of life on Earth, but also in the evolution of life," said Bhattacharyya. "It makes sense that cells would utilize it in this way."
The study suggested that bacterial memories might trigger a rapid migratory swarm when iron levels are low, for example, to look for iron in the environment. But if iron levels are high, the environment is a probably a great place to hang out and form a biofilm, as indicated by their so-called memory.
"Iron levels are definitely a target for therapeutics because iron is an important factor in virulence," Bhattacharyya said. "Ultimately, the more we know about bacterial behavior, the easier it is to combat them."
Sources: University of Texas at Austin, Proceedings of the National Academy of Sciences (PNAS)