27.3.3 Viral Symbioses
Another good example of the importance of symbionts in the evolutive process can
be found in studying viruses and infectious subviral genetic parasites, which have
been drivers of speciation since the origin of life. These genetic elements are as well
key actors in RNA interactions and have been involved in the origin of group
identity (Villarreal 2004, 2009; Villarreal and Witzany 2019). They are also important drivers in host evolution and concomitant evolution of biodiversity as has
become clear from the content and regulation of chromosomes of host cells. There
are indications that viral symbioses may have contributed to the origins of nuclei and
might also be involved in chromosomal replication (Villarreal and Ryan 2011).
The discovery that part of the human genome and genomes of other mammals are
of viral origin leads us to consider the importance of horizontal gene transfer in
evolution and in the shaping of life on Earth. Since viruses can adapt rapidly to new
environments, viruses might allow for the host to adapt faster and efficiently to new
environmental conditions through the introduction of new genomic elements
(Villarreal 2004, 2009; Villarreal and Witzany 2019). We suggest that an important
evolutive interphase between new viruses and the human body as a host can be found
at our gastrointestinal system, where a permanent and well-adapted community of
microbial organisms coexist, allowing for the sharing and incorporation of new
genetic information and adaptation by the viruses when they attempt to communicate
and to establish a stable symbiotic relationship with human populations via
symbiogenic mechanisms. Probably this is the case of the new coronavirus responsible for the disease Covid-19 and we are experiencing in this first phase of the
outbreak the establishment of a genetic relationship which is, for now, temporarily
more lethal for the host.
27.3.4 The Human Gut Microbiome
To understand the global importance of symbionts in relation to their host organism,
we must refer to and discuss the gastrointestinal microbiome in humans.
The human microbiome consists of all microbial organisms and their genetic
content in and on the human body and can be considered an intricate and complex
ecosystem in which symbiotic bacteria, archaea, fungi, protists, and viruses coexist
in the gastrointestinal system, on the skin and within others parts of the body. The
gut microbiota represents the largest number and concentration of microorganisms in
the human body, with the colonization of the intestinal tract starting at birth
(Haahtela 2019; Salazar et al. 2017; Sender et al. 2016).
In 1886, Theodor Escherich (1857–1911), a German born physician, published a
postdoctoral thesis as a monograph entitled The intestinal bacteria of the infant and
their relation to the physiology of digestion, where he describes his findings on
Bacillus coli commune (later named Escherichia coli) present in healthy infants and
604
F. Carrapiço
Another good example of the importance of symbionts in the evolutive process can
be found in studying viruses and infectious subviral genetic parasites, which have
been drivers of speciation since the origin of life. These genetic elements are as well
key actors in RNA interactions and have been involved in the origin of group
identity (Villarreal 2004, 2009; Villarreal and Witzany 2019). They are also important drivers in host evolution and concomitant evolution of biodiversity as has
become clear from the content and regulation of chromosomes of host cells. There
are indications that viral symbioses may have contributed to the origins of nuclei and
might also be involved in chromosomal replication (Villarreal and Ryan 2011).
The discovery that part of the human genome and genomes of other mammals are
of viral origin leads us to consider the importance of horizontal gene transfer in
evolution and in the shaping of life on Earth. Since viruses can adapt rapidly to new
environments, viruses might allow for the host to adapt faster and efficiently to new
environmental conditions through the introduction of new genomic elements
(Villarreal 2004, 2009; Villarreal and Witzany 2019). We suggest that an important
evolutive interphase between new viruses and the human body as a host can be found
at our gastrointestinal system, where a permanent and well-adapted community of
microbial organisms coexist, allowing for the sharing and incorporation of new
genetic information and adaptation by the viruses when they attempt to communicate
and to establish a stable symbiotic relationship with human populations via
symbiogenic mechanisms. Probably this is the case of the new coronavirus responsible for the disease Covid-19 and we are experiencing in this first phase of the
outbreak the establishment of a genetic relationship which is, for now, temporarily
more lethal for the host.
27.3.4 The Human Gut Microbiome
To understand the global importance of symbionts in relation to their host organism,
we must refer to and discuss the gastrointestinal microbiome in humans.
The human microbiome consists of all microbial organisms and their genetic
content in and on the human body and can be considered an intricate and complex
ecosystem in which symbiotic bacteria, archaea, fungi, protists, and viruses coexist
in the gastrointestinal system, on the skin and within others parts of the body. The
gut microbiota represents the largest number and concentration of microorganisms in
the human body, with the colonization of the intestinal tract starting at birth
(Haahtela 2019; Salazar et al. 2017; Sender et al. 2016).
In 1886, Theodor Escherich (1857–1911), a German born physician, published a
postdoctoral thesis as a monograph entitled The intestinal bacteria of the infant and
their relation to the physiology of digestion, where he describes his findings on
Bacillus coli commune (later named Escherichia coli) present in healthy infants and
604
F. Carrapiço