Two articles published in Science in microbial systems analyze the genetic changes that are necessary to incorporate new physical traits advantageous. In the first experiment analyzed the co-evolution of bacteriophage lambda and host regular, E. Coli, and the second response from the E. Coli to changes in temperature.
“Under the right conditions, the virus can develop new features quickly and repeatedly. The way in which their host evolves with them determines which traits are manifested,” says Justin Meyer, a researcher at Michigan State University (USA) and author of an article published in Science in which he examines the evolutionary forces responsible for the emergence of a new trait in the species.
To do this, Meyer and his team did an experiment with the virus that infects E. Coli (called bacteriophage lambda) and the bacteria itself. “We investigated how the virus develops a new ability that allows it to infect its host through an ancestral receptor that viruses could not use” described in the article.
Allowed the microbial system evolved together under laboratory conditions and found that after four key mutations, the organism developed the ability to adhere to a different bacterial host. Two of the changes were repeated in all experiments. The researchers also found that the bacteria responded with certain mutations in the virus changes, so that the evolution of bacteriophage lambda depends on its bacterial host.
Scientists regulated in certain laboratory conditions that caused the host bacteria develop resistance to the infectious agent, regulating the receptor OmpB, which ‘closed door’ to the virus. In these circumstances, the organism was forced to find a new route of entry: protein OmpF. “The virus develops many mutations to exploit a new receiver. All that found in the genome sequencing were in J protein, which is the key to ‘enter’ on your host,” says Meyer.
The researchers replicated the experiment in 25 different cases and noted that there had developed a new function: the bacteria could enter through a new path. Although viruses had reached this ability following different paths, in all cases had the same four kinds of mutations. “Therefore, four variations are needed to develop the new skill,” says Meyer. The role of natural selection in the adaptation process is very important, but the emergence of key innovations is less clear, because when the selection set certain variants that improve existing functions, you can limit the populations to reach their avoid local maxima and discover new skills. “Natural selection helped set the mutations in the recognition of the host protein, which improved the ability of the original recipient and paved the way for other mutations that allow infection by a new receiver,” say the researchers. After this experiment, the researchers said: “The selection process is important for the evolution of a new function, but requires many mutations.”
In the second experiment, the researchers exposed 155 populations of E. Coli at high temperatures and observed what changes caused the condition of the genome for 2,000 generations. They identified 1,331 mutations, most of them in the genes and protein complexes, and also a few in the nucleotides. “We cannot quantify the adaptation to high temperatures as a trait, is a continuum in which strains respond much better adapted to their environment,” said Olivier Tenaillon, study author and researcher at the University of California (USA.)
“There are an unlimited number of routes adaptive mutations, but only a few in the functions,” said Tenaillon. “Two strains that have evolved independently share almost all functional units without having the same mutations.” From these results, scientists say that the interaction between genes for a given feature-epistasis-is a key mechanism for organisms to adapt to their environment.