At some point, most of us have probably been told by the dentist that we need to brush more as we have dental plaque building up. But what is dental plaque and what could it tell us about ancient humans?
Dental calculus (plaque) is ubiquitous on modern human teeth; it forms when a biofilm of oral bacteria builds up on the teeth and calcifies. As calcium phosphate mineral salts deposit on the tooth surface the biofilm becomes ‘trapped’ and preserved (Weyrich et al. 2015). This happens constantly over the individual’s lifetime trapping layer upon layer of bacteria. While dental plaque is often discarded from both live and dead individuals it is now recognised that this plaque contains bacteria that can be identified. Luckily for us ancient (and modern) hunter-gatherer groups don’t brush their teeth!
Image credit: http://www.sciencedaily.com/releases/2012/05/120502184838.htm
As this dental plaque is in a pre-fossilised state when the individual dies it is well preserved, resisting decomposition processes in the soil (Warinner et al. 2015). Scanning microscopy of dental calculus has shown the presence of whole bacteria from a number of taxa (Dobney and Brothwell 1988), but this microscopy is not good enough to determine species, so genetic sequencing must be employed.
The field of paleomicrobiology is rapidly advancing thanks to recent advances in biomolecular sequencing. Next generation sequencing, developed in the 90s, has allowed for culture free analysis of bacterial assemblages (Warinner et al. 2015) meaning that dead cells can be analysed, as found in this ancient dental plaque. This sequencing has revolutionised the view we have on the microorganisms found in our bodies (known as the human microbiome). The development of PCR in the 80s was the first major step in being able to characterise our microbiome.
The human microbiome contains a vast amount of bacterial cells (~1014) even outnumbering our own (~1013) and bacterial genes also outnumber our own (Warinner et al. 2015). It has been known for a long time that the human microbiome is implicated in human health (see Table for a summary of research on microbiome and health), and is often described as another ‘organ’. Despite this, the evolution of the microbiome is poorly understood. Knowing just how intrinsically linked our health is to our microbiome it could be suggested that to truly study and understand the physiology, development, behaviour and evolution of humans we must also study the evolution of our microbiome.
The successful characterisation of past oral microbiomes, and perhaps a determination of the gradual change over life time (possible due to the build up and lack of remodelling of dental calculus), could redefine questions on human health, disease transition, bacterial evolution, diet and overall health of past human communities.
Table. Brief summary of just some of the research into the link between human health and our microbiome
|Ruth (2010)||Review article summarising findings||Obesity associated with a shift in the representation of dominant phyla of microbiome||Gut microbiota impact inflammation and adipiosity via interactions with gut cells|
|Yatsunenko et al. (2012||Characterised the microbiome of humans at different ages||Found that there is a shift in bacterial assemblages and differences between ethnic and societal groups||That there is a need to consider the microbiome when evaluating human development, nutrition and physiological variations|
|Devaraj et al. (2013)||Review article looking at current evidence for link between diabetes and microbiome||Gut microbiota affect nutrient acquisition, energy harvest and a myriad of host metabolic pathways||Advances in the human microbiome project and metagenomics research will pave the way towards a greater understanding|
|Cryan et al. (2012)||Variations in the composition of the microbiome influence physiology and contribute to disease||Gut microbiota can also interact with the CNS and influence brain function and behaviour||The emergence of a microbiome-brain axis suggests modulation of the microbiome is a possible treatment for complex CNS disorders|
|Possemiers et al. (2011)||Incorporation of microbial metabolism as an important variable in the evaluation of bioactivity of molecules||Intestinal bacteria is closely involved in the metabolism of dietary compounds with a metabolic capacity that exceeds the liver with a factor of 100 for disposal of waste materials||Knowledge of this will improve the use of targeted product development, crucial for proper interpretation of the body’s response to chemicals (and drugs)|
|Grice and Segre (2013)||Considered the microbiome genome as a ‘second’ human genome||Source of genetic diversity, modifier of disease, essential component of immunity and affects metabolism||Microbiome and human genomes should be integrated if you are to get a ‘true representaiton’|
|Aas et al. (2008)||Used molecular methods to detect bacterial species associated with dental carries||Bacterial profiles changed with disease status and differ between primary and secondary dentitions||Oral microbiome implicated in the health of the teeth|
|Aas et al. (2005)||Characterise the bacterial diversity in a healthy human oral cavity||141 predominant species found, of which 60% have not been cultivated, 13 new species found||Distinctive predominant bacterial flora to the oral cavity that is highly diverse and subject specific, important to define oral microbiome before ful understanding of dental disease is possible|
|Grossi and Genco (1998)||Link between periodontal disease and diabetes||Found that upregulation of cytokine synthesis amplify the magnitude of glycation end product operative in diabetes mellitus||Controlling chronic periodontal infection is critical if long-term diabetes is to be control/treated|
|Schwabe and Jobin (2013)||Link between microbiome and cancer||Alterations (through environmental, dietary or lifestyle changes) of the microbiome may disturb the symbiotic relationship||Disturbances in the microbiome can promote diseases like cancer|
Aaa J, Paster B, Stokes L et al. (2005) Defining the normal bacteria flora of the oral cavity, Vol. 43, p5721-5732
Aas J, Griffen A, Dardis S et al. (2008) Bacteria of dental caries in primary and permanent teeth in children and young adults, Vol. 46, p 1407-1417
Cryan J and Dinan T (2012) Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour, Neuroscience, Vol. 13, p 701-712
Devaraj S, Hemarajata P and Versalovic (2013) The human microbiome and body metabolism: implications for obesity and diabetes, Vol. 59, p 617-628
Dobney K and Brothwell D (1988) A method for evaluating the amount of dental calculus on teeth from archaeological sites, Journal of archaeological science, Vol. 14, p343-351
Grice E and Segre J (2012) The human microbiome: our second genome, Annual review of genomics and human genetics, Vol. 13, p 151-170
Grossi S and Genco R (1998) Periodontal disease and diabetes mellitus: a two-way relationship, Nature, Vol. 3, p 51-61
Possemiers S, Bolca S, Verstraete W and Heyerick A (2011) The intestinal microbiome: a separate organ inside the body with the metabolic potential to influence the bioactivity of botanicals, Vol. 82, p 53-66
Ruth E (2010) Obesity and the human microbiome, Gastroenterology, Vol. 26, p 5-11
Warinner C, Speller C, Collins M et al. (2015) Ancient human microbiomes, Journal of human evolution, Vol. 79, p125-136
Weyrich L, Dobney K and Cooper A (2015) Ancient DNA analysis of dental calculus, Journal of human evolution, Vol. 79, p119-124
Schwabe R and Jobin C (2013) The microbiome and cancer, Nature reviews cancer, Vol. 13, p 800-812
Yatsunenko T, Rey F, Manary M et al. (2012) Human gut microbiome viewed across age and geography, Nature, Vol. 486, p 222-227