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Symbionts, Commensals and Facultative Pathogens
Certainty Style Key
Hover over keys for definitions:
True
Likely
Speculative
Human Uniqueness Compared to "Great Apes":
Speculative DifferenceMOCA Domain:
EcologyChimpanzees are omnivorous primates. The composition of their gut microbial communities generally reflects their diet. However, it should be noted that to date, the molecular-based study of the diversity of bacteria inhabiting the chimpanzee gut has been performed on captive animals only (two individuals housed at the St Louis Zoological Society). The gut microbes of chimpanzees, as assessed by sequencing of 16S rRNA genes (a phylogenetic marker for microbes) derived from fecal samples, are dominated by members of two phyla of Bacteria: the Firmicutes and Bacteroidetes. This is the same pattern as seen in mammals overall, and in humans in the same proportion. In addition to these two groups, which constitute the majority of bacteria present, other phyla detected in chimpanzee feces include Spirochaeates, Actinobacteria, and most surprisingly, members of a "candidate" phylum DSS1. This latter phylum is known from its 16S rRNA genes only: members of this phylum have not been cultured in the laboratory and thus their role and physiology are totally unknown. Apart from the DSS1 bacteria, the other phyla are also found in humans and other omnivorous primates, although the exact bacterial species represented in each animal species may be different. This reflects both the tremendous diversity of the gut microbiotas of mammals in general, and the very small number of samples that have been studied.
Background Information:
The gut bacteria of mammals are highly diverse and generally the composition of a mammal's gut microbes reflects their diet. For instance, herbivores harbor more similar suites of bacteria compared to carnivores. The richness of the gut microbiota is also related to diet, with herbivores generally harboring the most complex microbial assemblages (highest number of "species" of microbes), and carnivores the least. This presumably reflects the need for microbial assemblages to work together to break down complex polysaccharides from plants, whereas richer, simpler diets comprised of meats are more easily broken down and do not require specialized enzymes or thermodynamically-based microbial symbioses. There is an additional force shaping the gut microbial communities of mammals: animals with similar gut physiologies tend to have similar microbial communities (eg, foregut fermenters vs hindgut fermenters). In this context, chimpanzees and humans have similar diet, gut structures and thus both species have grossly similar gut microbial assemblages typical of omnivorous primates.
The Human Difference:
To date, very little information is available to compare the gut microbes of chimpanzees and humans. What data do exist to not reveal any major differences between the bacterial assembales of humans and chimpanzees. From the standpoint of the microbial ecology of the gut, humans and chimpanzees both appear to be fairly typical omnivorous primates. The chimpanzees microbiotas that have been studied are a little more similar to those of folivorous monkeys than the human samples are, which might reflect the higher fiber content of the chimpanzee diet relative to the average Western human.
Universality in Human Populations:
Humans are by far the most studied animal, and this is true for the characterization of the microbial assemblages in the gut as well. So far, DNA-based studies of the human gut microbes indicate that 2-3 phyla are dominant in people (Firmcites, Bacteroidetes, Actinobacteria) but that the specific suite of bacteria from these phyla varies greatly from person to person, such that there isn't a single "species" (as defined by 16S rRNA gene phylogeny) that is at 0.5% or higher in all people ( this is based on approx 150 people studied). What people do have in common is the functional genes represented by these bacteria: although the specific lineages of bacteria present my differ, the genes they encode are similar between people. Thus, the gut bacteria have a tremendous amount of functional redundancy and many different mixes of "species" appear to be able to carry out the same tasks for the host, such as degradation of the diet, vitamin production, etc.
Mechanisms Responsible for the Difference:
Not known
Implications for Understanding Modern Humans:
To date there is very little information on the microbiology of the wild chimpanzee. Since the gut microbes are implicated in energy balance, and in contributing to the body weight of the host, a greater understanding of the differences between humans and their close relatives may shed light on whether gut microbes helped shape the evolution of humans and in particular if they played a role in the proposed trade-off bewteen large gut and large brain.
References:
Ley RE, Hamady M, Lozupone C, Turnbaugh PJ, Ramey RR, Bircher JS, Schlegel ML,Tucker TA, Schrenzel MD, Knight R, Gordon JI.Science. 2008. Evolution of mammals and their gut microbes.Jun 20;320(5883):1647-51.
Occurrence in Other Animals:
As stated above, the gut microbes of chimpanzees studied to date are typical of those of other omnivorous primates. However, studies of wild chimpanzees in their native habitats are required to gain a more realistic view of the diversity of their gut microbes in comparison to humans.