As I get older (I’m 43), I find myself coming back to my love of science (MSc in Electrical Engineering, but that was half my life ago….) in part, prompted by questions my children ask. As a sometimes sufferer of “IBS”, I’m interested in following the latest science in this area, and your work very much hits home. Please keep it up, and thank you for taking the time to respond to my modest questions.

These are insightful questions!

1) Although many bacterial strains and genes are common and shared among many of us, we do suspect that each person harbors their own, unique bacterial community (possibly enabling forensic use as described here: http://www.pnas.org/content/107/14/6477). Although we know this is true at the species level, we’re still unclear whether its true at the level of transferred genes – this is an active area of research in our lab at the moment. Your second question about the difficulty of defining bacterial species in the context of promiscuous HGT highlights a deep, open problem in the microbiology community. I’m afraid I don’t have much additional insight to offer here, although I’ll point out that its possible that a core set of genes are transferred much less than the mobile set that we studied. Although the promiscuous nature of HGT means that the concept of ‘species’ among bacteria is undoubtedly quite different from what we think of among vertebrates etc, it is possible to trace bacterial lineages from these core genes which are transferred much less frequently.

2) Bacterial communities are established quickly after birth (http://www.pnas.org/content/early/2010/07/27/1000081107) but are not believed to assemble in utero. This community assembly process is likely critical for proper immunological development and inadequate or inappropriate exposure underlies the so called ‘hygiene hypothesis’ for many immunological disorders observed in developed countries.

3) You’ve addressed another very important open question in the field here. This is an area of very active research in ours and other groups. You can expect some interesting results will be published to address these questions in the near future!

4) IgA is one of several important mechanisms by which our immune systems interact with our microbiota. Although it is almost certain that host immunity plays an important role in shaping our bacterial communities, we haven’t yet determined exactly what the implications are of these interactions.

These are great points – we’re happy to answer more questions as they arise!

All the best,
Mark

Some very interesting research. I do have some questions:

1. Does it follow from your findings that each human, in creating a unique “market-place”, could have a unique population/species of bacteria found no where else? Is it possible to define separable species in this context, when there is such widescale trading of genetic material?

2. How quickly in the life of a human does the “marketplace” get established? Does it happen in utero (and if so, how do they get there?), or, within the days and weeks after birth?

3. Do the residents change with changes in age and diet, or, do the existing residents adapt to the changing environment genetically, or, do they simply switch on/off existing protein catalysts (where they have them) to respond to shifts in food availability?

4. How does the production of IgA in the mucosal lining of the intestine influence the “marketplace”?