Who nose why skin's the way it is

Today I read about an interaction between two occupants of the human microbiome. The authors really do their findings a disservice by repeatedly referring to them in the context of the "nostril microbiome". What they really discuss is Staphylococcus aureus and various species of Propionibacterium. Both can be found in a variety of skin locations and especially on the face. Propionibacterium - and especially P. acne - is famous for causing the inflammation associated with all manner of nasty skin conditions. S. aureus is famous for causing many similar but often more medically worrisome infections. This paper shows how they might work together.*

Long story short: it's coproporphyrin IIIPropionibacterium produces it and S. aureus uses it as a sign to start making biofilms.  A biofilm phenotype can improve survival in the face of the immune system, antibiotics, or even just physical stress.

Wollenberg, M. S., Claesen, J., Escapa, I. F., Aldridge, K. L., Fischbach, M. A., and Lemon, K. P. (2014). Propionibacterium-Produced Coproporphyrin III Induces Staphylococcus aureus Aggregation and Biofilm Formation. mBio 5, e01286-14-.

*Anthropomorphism is to be avoided when discussing microbes. The English language, unfortunately, offers many opportunities for anthropomorphism-based rhetoric. In this case, "work together" is a bit misleading as this may not be a coordinated biological phenomenon. It may simply result from one species releasing a molecule and another species noticing it.