Indeed, mammalian cells are also unable to digest most
polysaccharides of plant origin except starch, which therefore
depends on the human microbiota. Active anaerobic intestinal
bacteria in the gut, anoxic, are similar between humans and
animals. Recent work confirms the existence of mutualistic
bacteria in the human gut. Indeed, the genomes of the obligate
anaerobic bacteria Bacteroides, the dominant human gut bacterial genus, confirm the presence of genetic determinants and
proteins involved in the degradation of polysaccharide
compounds (Xu et al. 2003). In addition, inoculation to laboratory mice devoid of microbiota and maintained under axenic conditions, of strain Bacteroides thetaiotaomicron VPI5482 isolated from the human intestine, leads to a pleiotropic
effect: activation of carbon metabolism and storage of lipid
compounds (Ba ¨ckhed et al. 2004), stimulation of cells producing antimicrobial compounds, and microvilli of the intestinal wall (Stappenbeck et al. 2002; Hooper et al. 2003).
Another effect called probiotic* was supported by some
data. The concept of probiotics has been proposed by the
Russian Nobel Prize winner Elie Metchnikoff. It is defined
as any living microorganism which, when ingested at a certain
amount, exerts beneficial effects beyond basic nutritional
functions. The probiotic microorganisms most frequently
cited are lactobacilli and bifidobacteria, and the reported
effects range from changing the intestinal ecology to the
stimulation of the immune system or the decrease of the risk
of cancer (Ouwehand et al. 2002). The probiotic issue has
generated many controversies.
The prevalence and persistence across generations of
microbes that play an important role in nutrition, in immunity, and in development are clear proof of the mutualistic
nature of animal-microbe associations.
11.4.3.4 Commensalism, Parasitism, and Other
Interactions with Intermediate
Phenotypes
Overview
A large number of microorganisms that live on the surface
and in the internal organs of animals benefit from this habitat
without producing observable effects in their hosts. These
are microorganisms known as commensals, among which
are mainly bacteria such as Pseudomonas, Acinetobacter,
and Bacillus in insects or E. coli, Staphylococcus, Corynebacterium, and Lactobacilli in mammals. Some of these
bacterial taxa are also, as noted above, the pathogenic or
mutualistic flora. Commensal microbiota that colonizes the
surface of a given organ can prevent through a physical
barrier effect the colonization of other bacteria, including
pathogens. In contrast, the commensal microflora may represent a hazard to animal health as some groups carry genes
for antibiotic resistance that may be acquired by pathogens
by transformation, conjugation, or transduction. Transfer of
antibiotic resistance genes between bacteria of animal and
human origin has been identified in the gastrointestinal tract
of animals (Moubareck et al. 2003). It has been seen that
many commensal microbes colonize the skin or integument
of animals. Some of them are involved in the production of
volatile and odorous molecules that may have a direct or
indirect impact on health. This is particularly the case of
compounds of microbial origin that act as attractants toward
mosquitoes (Brady et al. 1997) whose bites cause viral or
parasitic infections.
Genomics can allow comparative research on the
differences and similarities at the genetic and functional relationship between commensal microbes, parasites, and mutualistic animals. The distinction between these interactions is
sometimes difficult to establish. Whether pathogenic or mutualistic, commensal or parasitic, microorganisms share common genetic determinants and adaptations that allow them to
colonize many environments (Hentschel et al. 2000; Goebel
and Gross 2001). The similarity of the processes involved in
the expression of a bipartite or multipartite symbiotic interaction can lead to intermediary phenotypes that are not always
obvious to position in traditional categories (pathogenesis,
parasitism, cooperation, mutualism, etc.).
Wolbachia and Phenotypic Pleiotropy
The case of bacteria of genus Wolbachia is exemplary
because they establish associations with their hosts yielding
multiple phenotypes (pleiotropy*) which lie in the
parasitism–mutualism continuum. These alphaproteobacteria of the order Rickettsiales infect filarial nematodes
of the family Onchocercidae and many arthropods such as
mites, crustaceans, and insects (Werren et al. 1995; Bandi
et al. 2001). Wolbachia is mutualistic of filarial nematodes
that include human pathogens such as Onchocerca volvulus
involved in human onchocerciais or river blindness or
Wuchereria bancrofti or Brugia malayi both responsible
for elephantiasis. Bacteria are located in the hypodermal
cells of the lateral chords of larvae but also in the ovaries
in adult females and are thus transmitted transovarially to
offsprings (Taylor et al. 1999; Fisher et al. 2011).
Polysaccharides of Wolbachia represent an aggravating factor in inflammatory processes associated with filariasis
(Saint Andre ´ et al. 2002). The elimination of Wolbachia by
antibiotics (rifampin, tetracycline) from infected nematodes
leads to inhibition of embryogenesis and larval development
(Bandi et al. 2001). Therapeutic trials combining antifilarial
drugs (albendazole and ivermectin) and antibiotics
(tetracyclines) have been conducted with some success
against infection with Wuchereria bancrofti (Turner et al.
2006; Johnston and Taylor 2007).
In arthropods, Wolbachia induces multiple effects to the
hosts. A pathogenic effect has been shown in drosophila;
Wolbachia strain wMelPop is able to grow at high densities in
nervous tissue and causes fatal bacteremia (McGraw et al.
2002). However, in most cases, Wolbachia manipulates the
reproduction of their arthropod hosts. Four effects of
432
Y. Moe ¨nne-Loccoz et al.
polysaccharides of plant origin except starch, which therefore
depends on the human microbiota. Active anaerobic intestinal
bacteria in the gut, anoxic, are similar between humans and
animals. Recent work confirms the existence of mutualistic
bacteria in the human gut. Indeed, the genomes of the obligate
anaerobic bacteria Bacteroides, the dominant human gut bacterial genus, confirm the presence of genetic determinants and
proteins involved in the degradation of polysaccharide
compounds (Xu et al. 2003). In addition, inoculation to laboratory mice devoid of microbiota and maintained under axenic conditions, of strain Bacteroides thetaiotaomicron VPI5482 isolated from the human intestine, leads to a pleiotropic
effect: activation of carbon metabolism and storage of lipid
compounds (Ba ¨ckhed et al. 2004), stimulation of cells producing antimicrobial compounds, and microvilli of the intestinal wall (Stappenbeck et al. 2002; Hooper et al. 2003).
Another effect called probiotic* was supported by some
data. The concept of probiotics has been proposed by the
Russian Nobel Prize winner Elie Metchnikoff. It is defined
as any living microorganism which, when ingested at a certain
amount, exerts beneficial effects beyond basic nutritional
functions. The probiotic microorganisms most frequently
cited are lactobacilli and bifidobacteria, and the reported
effects range from changing the intestinal ecology to the
stimulation of the immune system or the decrease of the risk
of cancer (Ouwehand et al. 2002). The probiotic issue has
generated many controversies.
The prevalence and persistence across generations of
microbes that play an important role in nutrition, in immunity, and in development are clear proof of the mutualistic
nature of animal-microbe associations.
11.4.3.4 Commensalism, Parasitism, and Other
Interactions with Intermediate
Phenotypes
Overview
A large number of microorganisms that live on the surface
and in the internal organs of animals benefit from this habitat
without producing observable effects in their hosts. These
are microorganisms known as commensals, among which
are mainly bacteria such as Pseudomonas, Acinetobacter,
and Bacillus in insects or E. coli, Staphylococcus, Corynebacterium, and Lactobacilli in mammals. Some of these
bacterial taxa are also, as noted above, the pathogenic or
mutualistic flora. Commensal microbiota that colonizes the
surface of a given organ can prevent through a physical
barrier effect the colonization of other bacteria, including
pathogens. In contrast, the commensal microflora may represent a hazard to animal health as some groups carry genes
for antibiotic resistance that may be acquired by pathogens
by transformation, conjugation, or transduction. Transfer of
antibiotic resistance genes between bacteria of animal and
human origin has been identified in the gastrointestinal tract
of animals (Moubareck et al. 2003). It has been seen that
many commensal microbes colonize the skin or integument
of animals. Some of them are involved in the production of
volatile and odorous molecules that may have a direct or
indirect impact on health. This is particularly the case of
compounds of microbial origin that act as attractants toward
mosquitoes (Brady et al. 1997) whose bites cause viral or
parasitic infections.
Genomics can allow comparative research on the
differences and similarities at the genetic and functional relationship between commensal microbes, parasites, and mutualistic animals. The distinction between these interactions is
sometimes difficult to establish. Whether pathogenic or mutualistic, commensal or parasitic, microorganisms share common genetic determinants and adaptations that allow them to
colonize many environments (Hentschel et al. 2000; Goebel
and Gross 2001). The similarity of the processes involved in
the expression of a bipartite or multipartite symbiotic interaction can lead to intermediary phenotypes that are not always
obvious to position in traditional categories (pathogenesis,
parasitism, cooperation, mutualism, etc.).
Wolbachia and Phenotypic Pleiotropy
The case of bacteria of genus Wolbachia is exemplary
because they establish associations with their hosts yielding
multiple phenotypes (pleiotropy*) which lie in the
parasitism–mutualism continuum. These alphaproteobacteria of the order Rickettsiales infect filarial nematodes
of the family Onchocercidae and many arthropods such as
mites, crustaceans, and insects (Werren et al. 1995; Bandi
et al. 2001). Wolbachia is mutualistic of filarial nematodes
that include human pathogens such as Onchocerca volvulus
involved in human onchocerciais or river blindness or
Wuchereria bancrofti or Brugia malayi both responsible
for elephantiasis. Bacteria are located in the hypodermal
cells of the lateral chords of larvae but also in the ovaries
in adult females and are thus transmitted transovarially to
offsprings (Taylor et al. 1999; Fisher et al. 2011).
Polysaccharides of Wolbachia represent an aggravating factor in inflammatory processes associated with filariasis
(Saint Andre ´ et al. 2002). The elimination of Wolbachia by
antibiotics (rifampin, tetracycline) from infected nematodes
leads to inhibition of embryogenesis and larval development
(Bandi et al. 2001). Therapeutic trials combining antifilarial
drugs (albendazole and ivermectin) and antibiotics
(tetracyclines) have been conducted with some success
against infection with Wuchereria bancrofti (Turner et al.
2006; Johnston and Taylor 2007).
In arthropods, Wolbachia induces multiple effects to the
hosts. A pathogenic effect has been shown in drosophila;
Wolbachia strain wMelPop is able to grow at high densities in
nervous tissue and causes fatal bacteremia (McGraw et al.
2002). However, in most cases, Wolbachia manipulates the
reproduction of their arthropod hosts. Four effects of
432
Y. Moe ¨nne-Loccoz et al.