Why is showering bad for our skin bacteria? (evolutionary questions)

After reading Alanna Collen’s 2015 book 10% Human: how your body’s microbes hold the key to health and happiness, I have become interested in, among other topics featured in the book, the work of the AOBiome company. Collen mentions this company in the context of aspects of our modern lifestyle which may be detrimental to the beneficial microbes that live on and in us. In this particular case, it is the practice of showering every day with body soap and deodorant that may be disproportionately displacing certain types of bacteria that process ammonia and help control the bacteria responsible for giving us body odor. AOBiome proposes that by replenishing these ammonia-oxidizing bacteria (AOBs) on our skin, we can reduce or eliminate the need for deodorants and showers. We can also replenish them through contact with soil or untreated (an unpolluted) water, according to Collen. I have read up on AOBiome a bit, and their scientific logic seems sound and is backed up by pilot studies they have done (see end for links). However, I have some questions about the evolutionary biology side of things:

  1. Are AOBs meant to permanently colonize our skin, or even if we never showered would their populations be naturally supplemented through our contact with water and dirt, where they reside? I.e. is there selection pressure for them to adapt to life on human skin versus life in soil or water?
  2. If AOBs have historically (pre showers) colonized human skin on a long-term basis, how have they adapted to the enrivonment and the other members of its bacterial community?
  3. Has our modern personal hygeine regimen been so extreme as to afford them no opportunity to adapt? This might be explained if their populations would otherwise be regularly replenished from the outside environment. Otherwise, I would be surprised if they have not adapted at least a little bit to the showering situation. Humans have been showering for longer than antibiotics have been in use, and resistance to antibiotics did not take long to crop up. Granted, Nitrosomonas eutropha, the particular AOB used by AOBiome, has a doubling time on the order of 10 or more hours (see end for links), which is much longer than that of the pathogens targeted by antibiotics. It’s even longer than my notoriously slow-growing bacterium, Myxococcus xanthus. This could be a definite downside when rapid adaptation is necessary. Also, it may be the case that adaptation within a species such as N. eutropha may not be possible becasue selection might first act on the standing genetic variation within the community, which includes some species better able to withstand a deluge of hot water. These species would then crowd out N. eutropha and other AOBs in competition for space and other shared resources.
  4. Has anyone done a growth rate vs temperature curve for AOBs, and N. eutropha in particular? How does their growth rate compare in human body temperatures versus typical soil or water temperatures?
  5. Would an experimental evolution type approach to culturing AOBs be able to produce adapted strains that can handle some aspects of modern hygiene, such as short warm showers?

Links to my sources:

AOBiome’s scientific logic (2 posts on their website about AOBs and their effect on skin): http://aobiome.com/aob-skin-conditions; http://aobiome.com/nitric-oxide

Info on AOBiome’s first pilot study from a participant, and generation time of N. eutropha (2014 New York Times article): https://www.nytimes.com/2014/05/25/magazine/my-no-soap-no-shampoo-bacteria-rich-hygiene-experiment.html

More generation time: Fujitani, Hirotsugu et al. “Selective Isolation of Ammonia-Oxidizing Bacteria from Autotrophic Nitrifying Granules by Applying Cell-Sorting and Sub-Culturing of Microcolonies.” Frontiers in Microbiology 6 (2015): 1159. PMC. Web. 2 July 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4607866/

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