Followers of these pages will have noted the increasing intrusion of bugs — the microbes that co-habit our bodies, known as the microbiome. This has reflected the fact that their importance has been gradually revealed to the extent that we now know that they affect cancer, obesity and even how inclined you are to take physical exercise. Indeed in the previous blog we looked at new results showing how bacteria affect bowel cancer (in Mapping the bug army). Not surprising then that they are being referred to as ‘an organ in their own right’.
Now comes the next stage in highlighting the importance of the microbiome in the shape of a massive study that reveals what might have been predicted, though it’s still fascinating. ‘Our microbiome is shaped by family, friends and even neighbours.’ That’s the upshot and I’ve put the sentence in italics because it is the title of a Nature editorial describing the paper (Callaway, 2023).
Family, friends and pets shape our lives — and our microbiome.
It’s the work of Mireia Valles-Colomer, Nicola Segata and colleagues at the University of Trento and the European Institute of Oncology in Milan who analysed the ‘metagenomes’ of nearly 10,000 stool and saliva samples. A metagenome is what you get when you do complete sequencing of all the genetic material you extract — in this case from human tissue. And that means you get the bacterial genomes as well.
What they found was extensive strain sharing across individuals with distinct patterns between mothers and their infants, within households and between population groups (e.g., between villages).
Person-to-person strain-sharing rates for the gut microbiome. These are ‘box plots’: the box edges mark upper and lower quartiles, the centre line is the median and the ‘whiskers’ extend to 1.5 times the interquartile range. The y axis (% strain-sharing rate) shows the percentage of the same bacterial strains that is shared between the two sources. The percentage figures along the top show the percentage of pairs between which no strain-sharing event was detected. From Valles-Colomer et al., 2023.
The upshot of this multi-cohort study was that there is extensive person-to-person bug transmission — not surprising but interesting to have confirmed. Thus the percentage shared by mother and offspring is just over 30%. For co-habiting persons the figure is about 12%.
What this means is that long-lasting, close contact is a key factor in shaping the genetic makeup of our personal microbiomes — and this is true both for our gut and oral microbiomes. Again, as you might expect, strain sharing was greatest between mother and infant gut microbiomes during the first year of life (median of 50%). However, shared strains also accounted for 12% and 32% of the gut and oral microbiome species in common between cohabiting individuals, respectively.
The study included samples from all over the world and a notable finding was that sharing was rather similar between Western populations and those from elsewhere — perhaps surprising as one might suppose that microbiome transmission would be harder to detect in societies with better public-health infrastructure.
The take home message is that, although the microbial communities that live in and on our bodies are now thought of an a specific organ and they evolve continuously throughout our lives, their basic composition is heavily dependent on our nearest neighbours.
References
Callaway, E. (2023). How our microbiome is shaped by family, friends and even neighbours. Nature.
Valles-Colomer, M., Blanco-Míguez, A., Manghi, P. et al. The person-to-person transmission landscape of the gut and oral microbiomes. Nature (2023).
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