Conjectures about microbial slimes

Slime thoughts inspired by a site visit to the Biofilm Center at Montana State University, Bozeman, Feb. 1996 :

Why do microorganisms attach to surfaces ?

Consider a bare surface in a stream that is low in nutrients. It makes sense that adsorption will increase local concentration and attract microorganisms. They attach and feed on nutrients more concentrated than those in the bulk. This advantage disappears because after these nutrients are depleted, the colony or slime covers the adsorption sites and prevents the arrival of new nutrients. Furthermore, these organisms have poorer mass transfer than a suspended organism that moves freely and can transfer in 3 dimensions. The potential mechanisms for the slime are:
  • deposition by sedimentation
  • adsorption, but a smooth slime would not be expected to have sites anywhere near as active as those in activated carbon
  • facilitated transport, this usually involves membranes, ion pumps, and the like. However, lectins or similar biochemicals that bind organic molecules might be excreted by slime organisms into their slime to aid the driving forces for mass transfer. If something binds the organic nutrient, it could be more concentrated than in the bulk. This binding would have to be broken easily by the organisms.

    Weak point: Concentration in the slime is very low, and this alone should be the driving force for mass transfer. Binding can't help unless the binding agent is positioned better along the route of mass transfer, e.g., on the surface of the slime. This is far-fetched because no organisms should expend its resources making the slime better for all the others. Conclusion: No active transport explanation.

    Further reflections: If the transport is by passive diffusion, the concentration in the slime approaches the concentration in the bulk asmyptotically. An organism in the bulk has the advantage. This leads to the conclusion that attachment is solely for the purpose of keeping the organism in the system. Those in the bulk go elsewhere to survive or die

  • Gradients in microbial slimes.
    last effort on 26-June-96