Bacterial Biofilms

This recent article in PLoS Biology gives a very readable review of bacterial biofilms and the kinds of problems they pose in medical settings. A familiar example of a bacterial biofilm is plaque on our teeth. Bacteria, when they reach a certain critical density on a surface, begin to aggregate and secrete a slimy polymeric matrix which aids further establishment and eventually builds up to a complex structure with channels and pores through which fluid can flow, carrying in nutrients and carrying away waste materials.

A few interesting points to think about:

• The means by which the bacteria detect the critical population density needed to form biofilms is called quorum sensing. How does it work?
  
• Previously it was thought that the slimy matrix protected bacteria by preventing them from being engulfed or attacked by other cells or substances, but the matrix has to be permeable to most substances because waste and nutrients must reach the bacteria. So how do they defend themselves?
  
• Biofilms usually form on surfaces over which there is regular fluid flow. Why would the biofilm growth form be advantageous?
  
• Bacteria living in biofilms reproduce at a slower rate than free living ones. How might this be understood by analogy to life-history trait selection in r- and K-selective environments?