"Holos" means whole in Greek and genome is of course all of the DNA in an organism. Thus, hologenome is the term that captures the intergenomic networkism present in every animal and plant and parallels the term holobiont - the sum of all organisms present in an animal or plant.
Microbe magazine published my book review of the Hologenome Concept: Human, Animal and Plant Microbiota. As good friend Dr. Laura Williams pointed out to me, the review is unfortunately under a paywall. I believe this book will strike a chord with everyone interested in the life sciences. It is a form of heightened pattern recognition in biology. Hence, I'm posting the original text of the review here.
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Eugene Rosenberg and Ilana
Zilber-Rosenberg (ed.). Springer, New York, 2014, 178 p., $149 (eBook) or
$189 (hardcover).
“So, like it or not, microbiology
is going to be in the center of evolutionary study in the future—and vice
versa.” -Carl Woese, The Hologenome Concept, pg. 109
In The
Hologenome Concept: Human, Animal and Plant Microbiota, Eugene Rosenberg
and Ilana Zilber-Rosenberg methodically advance the postmodern synthesis in
which the holobiont — the host plus its associated microorganisms— forge a
unique biological entity subject to the fundamental tenets of biological
evolution. This book is based on the popular idea that no “individual” plant
or animal, including Homo sapiens, exists independently of microbes.
The authors were in fact among the fırst serious advocates of this view and
have published a number of conceptual papers on the hologenome. Now backed by
a symphonic-like arrangement of hard evidence, The Hologenome Concept is
poised to be an influential piece of literature that encompasses biology’s
most signifıcant developments in the last decade. What has led Rosenberg and
Zilber-Rosenberg to this inflection point?
Looking back in history, the germ
theory of disease is a perfect starting point to put The Hologenome
Concept in context. The germ theory left two lasting legacies on biology.
First, it massively widened the focus of biology on diagnosing, treating, and
eradicating infectious diseases. Second, it narrowed biology’s focus on
microbes to such an extent that all host-associated microbes were essentially
viewed as harmful and thus extrinsic entities to animals and plants. Today,
there are of course a myriad of reasons to doubt that all microbes are bad
(indeed quite the opposite), and this shift in thinking gained notable
momentum in the mid- 20th century. Ivan Wallin’s and Lynn Margulis’s plights
in convincing biologists that mitochondria were bacterially derived were
among the seminal turning points in adjusting perceptions toward the broader
nature of evolution.
In the last few decades, microbiology has made
revolutionary contributions to all disciplines of biology. From Carl Woese’s
evolutionary tree of life to the universality of microbiomes in plants and
animals, there is a tangible sense that something substantial is affecting
how we study, understand, apply, and teach the life sciences. More than just
advances in technology and more than realizing the central importance of
microbiology in shaping life, the postmodern synthesis that we are now
witnessing is tackling additions and upgrades to theories that seem
untouchable, including the Darwin and Wallace theory of evolution by natural
selection.
Rosenberg and Zilber-Rosenberg demonstrate with precision that
this inflection point in the history of biology is not just a common sense
issue, but one that is scientifıcally grounded in a treasure of data.
Chapters are devoted to illustrating how the canonical mechanisms of
evolutionary change seamlessly fıt into a hologenomic unit of selection,
namely genetic variation in the hologenome, maternal transmission between
holobiont generations, and multi-level selection theory and fıtness. They
bring together a vivid recipe for how variation in plants and animals exists
beyond the nuclear genome, spanning microbial amplifıcation, acquisition of
novel microbes, and horizontal gene transfer. In particular, genetic
variation of complex organisms is not restricted to the nuclear genome and
cytoplasm, but to the general microbiome as well. This variation encodes
phenotypes subject to natural selection. Thus, the central tenet of the book
is that the hologenome is a newly appreciated unit of variation and evolution
in which the amalgam of genomes in the host and symbionts collectively are a
target of natural selection.
For those that have seen the central role of
symbiosis in biology, this book will be an essential reference of key papers,
defınitions, teaching, inspiration, and future discourse. It was for me. For
others that doubt the emerging horizon of the microbiome’s role in evolution,
this book will fuse their familiarities with frontier research to form a new
appreciation on how variation and selection on the host-associated microbiota
is equal to these same forces acting on the nuclear genome. Indeed in my own
analysis of the book, I have found it most helpful to ask, when are the
evolutionary properties of a nuclear gene any different than those of a
microbe in the microbiome? I have not yet been able to discriminate the two,
and this simple exercise is the essence of The Hologenome Concept.
The
book is written exceptionally clearly and provides bullet points at the end
of each chapter to emphasize key themes in the text. The fırst chapter is one
of the most important of the book because it frames the concepts and
definitions in such a clear manner that confusion over nomenclature, which
can be widespread in the early phases of introducing new concepts, is erased
in favor of a vibrant appreciation for a hologenomic level of selection. What
is and is not the hologenome makes the rest of the arguments seamlessly fall
into place. The hologenome is not a metagenome, superorganism, organ, or the
singular unit of selection in evolution. It is a body of scholarship that fıts
squarely into genetics and multilevel selection theory in which the genome,
DNA-containing organelles, and microbiome cooperate and clash to forge a
source of variation for evolution by natural selection and the origin of
species. The Hologenome Concept: Human, Animal and Plant Microbiota brings
forth an upgraded “grandeur in this view of life.”
Seth Bordenstein
Vanderbilt University
Nashville, Tenn. |
