Social interactions are very important for humanity. We know that our friends, colleagues and family -those that we interact with regularly - help shape us as people, our beliefs, our education, and our lifestyles. But did you know they can even influence us at the microscopic level by helping to shape our microbiomes? And moreover, friends of friends and even their friends can help to shape our microbiomes, according to research published recently by Francesco Beghini and colleagues.

The team studied how social networks impacted the gut microbiomes of 1787 adults from 18 isolated villages. These villages are deep in the jungles of Honduras, and social interactions are conducted face to face. The diets of the people in these villages are traditional and these individuals rarely took medications such as antimicrobials – that would have otherwise impacted their gut microbiome. Over half of the participants (62%) were female and less than half of the people studied were married (41.8%). The average age of participants was 41 years.

The team mapped the social interactions of the participants at two time points(2019/2020 and then two years later) and  sequenced their microbiomes at these time points. The relationships identified within the participants were classed as: partner/spouse (410), father (303), mother (594), sibling (1,059), child (427), close friends (1,627), spend free time (1,749), and personal or private conversation (1,902).

Pairs of people with a diverse range of relationships with each other (spouse, father, mother, sibling, child, close friend, free time, personal or private conversations) shared more microbial strains than those that had no or little interactions. Spouses and those that shared a household had the highest strain-sharing rates (13.9% and 13.8%, respectively). And those that have non-kin relationships and are from different households share 7.8% of microbial strains.  The strain-sharing rate drops to 4% between individuals who have no interactions but live in the same village, implying that the strain-sharing came about due to shared environments or network-wide sharing of strains (friends of friends). The lowest strain-sharing rate of 2% was seen between people living in different villages.

The frequency and extent of interaction between two people can also impact the microbiome sharing rate. For instance, those that greet each other with a kiss on the cheek had a strain-share rate of 12.9%. Those friends or relatives that they did not live with each other but met on an almost daily basis had a strain-sharing rate (7.1%) as opposed to seeing them on a weekly basis (6%) or a couple of times a month (4.8%).

Mothers are more likely to share strains with their children than fathers, which may be due to women spending more time at home and around their children. However, apart from this instance, women did not generally share more strains with their social network than men.

All these observations are interesting from an academic perspective, but how could the microbiome sharing rate be utilised practically? My thoughts are: 

• This data could one day be used to identify people’s close networks as part of forensic investigations, to predict people’s relationships
• To trace disease transmission. 
• Potentially, shared microbiomes could be used (alongside other parameters) to predict how groups of people would respond physically to new infectious diseases, or predict the likelihood of non-communicable diseases in neighbourhoods.

These are only some of the applications that I could think of, but I am sure there could be more. However, of course, much more in-depth research needs to be carried out before microbiome strain-sharing rates can become a useful and accurate tool, especially as the villagers in this study were selected because that lived a lifestyle that eliminated other microbiome-altering factors such as  antimicrobial usage.  These factors will of course influence the gut microbiomes of most world populations, and so need to be incorporated into future studies..

(Poster image credit: Image by Gordon Johnson from Pixabay)