These are a condensed and complete set of revision notes for the final exam of the S317 module: from genes to species. It covers EVERYTHING from EVERY topic you need to learn and is taken directly from the module material. I scored VERY highly on this exam and got a 1st overall. You wont need to d...
S317 Topic 8: Development and Aging Part 6: Aging and the Microbiota Condensed
1. The microbiota
The microbiota is the many communities of microbial symbionts living within, or on the surface of, organisms.
They may acquire nutrients, and in some cases protection, via their host organism.
Many microbial populations live in close association with other organisms, this issymbiosis.
Box 1.1 A note about symbiosis
The use and interpretation of the term ‘symbiosis’ vary considerably between different sources.
Symbiosis can mean relationship between different organisms of different
species that is of mutual benefit to both
Symbiosis can also be used in a broader sense to mean a relationship but
not one that it beneficial.
It is often more helpful to use more specific terms to describe the
relationship between ‘symbiotic’ organism
High throughput DNA sequencing and the increasing availability of reference sequences have allowed a recent
rapid expansion of knowledge of microbiota.
They have facilitated identification and characterisation of microbial species that constitute the microbiota.
The term ‘hologenome’ is used to describe the combined genomes of a host organism and its microbiota.
In the parasitic wasps there is evidence that the origin of new species through postzygotic isolation may involve an
interaction between not just genetic information in the host organism, but also the microbiome of the host
organism’s microbiota.
The microbiome: Collective genome of microbiota
Many studies on the microbiota have focused on humans and ruminant mammals and, to a lesser extent, on
laboratory mammals such as mice.
The gut microbiota has been a major focus of such research.
There is accumulating evidence that gut microbiota plays a role in early development of immune system and some
animal tissues, and influences development of some diseases.
Studies of the microbiota of non-model organisms are also increasingly being carried out.
Relatively few studies of microbiota have been performed in the model organisms used to study ageing, such
as C. elegans, but these have provided some unexpected and important information in support of the idea that the
microbiota can influence ageing and longevity.
Symbiotic microbial populations occur on, or in, many parts of the bodies of animals.
The gut microbiota
All animals that have a gut are host to populations of gut bacteria.
While all gut bacteria can be described as symbionts, living in close association with another organism of a
different species (the host), some more specifically derive benefits from the interaction (commensalism), and some
also confer a benefit to the host (mutualism).
Others, however, can be pathogenic.
Size and diversity of populations of gut bacteria vary according to host species, influenced by the environment.
Now that whole populations of microbiota in the gut (and other sites) can be analysed using molecular sequencing
techniques, it is also possible to investigate the effects of different environmental conditions on microbiota.
Factors that may cause a change in gut microbiota include the host’s diet, antibiotic use, ageing and exercise.
Diet has a large effect on the balance of different microbial species in the gut.
In mammals, the gut microbiota has also been shown to be linked to a number
of inflammatory conditions.
Changes to the gut microbiota also occur during the life course.
Studies have shown that the populations of microbes in the human gut change
throughout life, particularly in the first few years and in the elderly
From infancy to old age, the proportions of the intestinal microbiota that are
represented by Bacteroidetes and (to a lesser extent) Firmicutes increase at the expense of Proteobacteria.
There is little difference between childhood and adulthood, with the greatest changes occurring between infancy
and early childhood and in the elderly.
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