Similar genes had mutated in the different cultures, but not always by the same
mutations (Blount et al. 2018). Six populations even developed mutator phenotypes,
which, in some cases, later reverted (Good et al. 2017). The later invention of
genome sequencing allowed more thorough examinations of the extent and course
of mutation pathways in the populations. Examining the frozen stocks of past
generations allowed his group to delineate the course of evolution to a degree
never before seen. He compared this to having a complete fossil record of a lineage,
a dream of Darwin’s that had now come true (Lenski and Travisano 1994).
One of the most important developments of the LTEE was the evolution of a
strain that could grow on citrate, a carbon source that E. coli strains typically do not
use because they lack the ability to transport it into their cells. Citrate was being
produced by the cells in the cultures. This strain showed a diminished ability to use
glucose, so it could evolve independently of its parent strain (Blount et al. 2008).
Some have contended that this gave the first example of seeing a new species evolve.
Shorter cultivations can also yield important insights into evolutionary processes.
In 1998 Paul Rainey and Michael Travisano examined the phenomenon of adaptive
radiation to determine what mutational events underlay sudden adaptations to fill
new niches (Rainey and Travisano 1998). Using an extraordinarily simple system to
create different niches, they inoculated a culture of Pseudomonas fluorescens into
small flasks of liquid medium and simply left them unshaken. The cells rapidly
consumed the dissolved oxygen in the medium setting up an oxygen gradient in each
flask. Cells growing dispersed in the medium differed from those growing in mats on
the surface. P. fluorescens was chosen for these experiments because it shows
differences in colony morphology that are correlated with their niche preference,
specifically based on oxygen availability (Rainey et al. 1993). Their work showed
that the heterogenous environment provided competition that drove adaptive
radiation.
The spectrum of mutations available to a population to allow evolutionary
divergence has been shown to be a function of contingency, evolutionary history,
and the environment (Blount et al. 2018; Maharjan and Ferenci 2017). All of these
influences had been envisioned by Darwin as important factors in evolution.
Darwin thought that the question about how life started was beyond the purview
of science and was the basis of his contention that he could not call himself an
atheist, but, instead, an agnostic, a term coined by his friend Thomas Henry Huxley
(Barlow 1958). Using new sequencing technologies, investigators are examining
biological events very near that origin of life, so perhaps it is a question amenable to
scientific investigation after all. New metagenomes have found Archaea that have
several molecular traits in common with eukaryotes supporting the idea that eukaryotes arose through a fusion of archaeal and bacterial cells (Fournier and Poole 2018;
Spang et al. 2015), though this theory is highly controversial (Nasir et al. 2015;
Imachi et al. 2020). The application of Darwinian principles of evolution to cells as
they evolved to form multicellular entities is also being examined using microbes
(see review in Rainey et al. 2017).
Darwin’s Natural Selection can also be examined in detail using microbial
cultures. The mode of cultivation can be used to examine the effects of different
48
K. M. Noll
mutations (Blount et al. 2018). Six populations even developed mutator phenotypes,
which, in some cases, later reverted (Good et al. 2017). The later invention of
genome sequencing allowed more thorough examinations of the extent and course
of mutation pathways in the populations. Examining the frozen stocks of past
generations allowed his group to delineate the course of evolution to a degree
never before seen. He compared this to having a complete fossil record of a lineage,
a dream of Darwin’s that had now come true (Lenski and Travisano 1994).
One of the most important developments of the LTEE was the evolution of a
strain that could grow on citrate, a carbon source that E. coli strains typically do not
use because they lack the ability to transport it into their cells. Citrate was being
produced by the cells in the cultures. This strain showed a diminished ability to use
glucose, so it could evolve independently of its parent strain (Blount et al. 2008).
Some have contended that this gave the first example of seeing a new species evolve.
Shorter cultivations can also yield important insights into evolutionary processes.
In 1998 Paul Rainey and Michael Travisano examined the phenomenon of adaptive
radiation to determine what mutational events underlay sudden adaptations to fill
new niches (Rainey and Travisano 1998). Using an extraordinarily simple system to
create different niches, they inoculated a culture of Pseudomonas fluorescens into
small flasks of liquid medium and simply left them unshaken. The cells rapidly
consumed the dissolved oxygen in the medium setting up an oxygen gradient in each
flask. Cells growing dispersed in the medium differed from those growing in mats on
the surface. P. fluorescens was chosen for these experiments because it shows
differences in colony morphology that are correlated with their niche preference,
specifically based on oxygen availability (Rainey et al. 1993). Their work showed
that the heterogenous environment provided competition that drove adaptive
radiation.
The spectrum of mutations available to a population to allow evolutionary
divergence has been shown to be a function of contingency, evolutionary history,
and the environment (Blount et al. 2018; Maharjan and Ferenci 2017). All of these
influences had been envisioned by Darwin as important factors in evolution.
Darwin thought that the question about how life started was beyond the purview
of science and was the basis of his contention that he could not call himself an
atheist, but, instead, an agnostic, a term coined by his friend Thomas Henry Huxley
(Barlow 1958). Using new sequencing technologies, investigators are examining
biological events very near that origin of life, so perhaps it is a question amenable to
scientific investigation after all. New metagenomes have found Archaea that have
several molecular traits in common with eukaryotes supporting the idea that eukaryotes arose through a fusion of archaeal and bacterial cells (Fournier and Poole 2018;
Spang et al. 2015), though this theory is highly controversial (Nasir et al. 2015;
Imachi et al. 2020). The application of Darwinian principles of evolution to cells as
they evolved to form multicellular entities is also being examined using microbes
(see review in Rainey et al. 2017).
Darwin’s Natural Selection can also be examined in detail using microbial
cultures. The mode of cultivation can be used to examine the effects of different
48
K. M. Noll