13.2 Applications and skills

13.2.3 Environmental consequences of biofilms

  • Biofilms can form on solid surfaces, but also on the surfaces of fluids, or even suspended in stagnant fluids.
  • How quickly a biofilm develops depends on the species and population density, as well as abiotic factors such as surface porosity, humidity, pH and temperature. 

Using biofilms for sewage treatment

  • Sewage water must be stripped of nutrients in order to prevent eutrophication of ponds and lakes.
  • Eutrophication is an environmental hazard because excess nitrogen and phosphorus cause harmful algal blooms – a rapid accumulation of algae on the surface of water bodies.  

Figure 13.2.3a Biofilms in a trickle filter bedFigure 13.2.3a Biofilms in a trickle filter bed

  • Sewage wastes are irrigated over trickle beds, onto which biofilms of aerobic bacteria develop.
  • The solid layer has a large surface area for biofilm attachment, and the large air spaces between stones allows for good oxygen penetration.
  • Spraying increases aeration. As the wastewater trickles down through the biofilm slime, organic nutrients are removed.
  • The effluent liquid undergoes further treatment before being released.
  • Biofilms are effective at removing nutrients from sewage waste because they cannot easily be washed away.

Problems caused by biofilms

  • Accumulation of biofilms can cause environmental problems including:
    • clogging or corroding of pipes and drains
    • transfer of microorganisms in ballast water
    • contamination of surfaces in food production
    • contamination of hospital equipment and tools

Try it!

  • Suggest a reason for each of the following observations:
    • Contact lens solution contains antibacterial agents as well as surfactants, which are mildly abrasive.
    • Treating bacterial colonies with traditional antibiotics can stimulate biofilm formation.
    • In the presence of Lactococcus lactis (a non-pathogenic bacteria), the rate at which Listeria monocytogenes (a bacteria that causes gastrointestinal infections) forms biofilms is reduced.

Nature of Science: Improvements in apparatus

  • The image below was made using a confocal laser-scanning microscope. The microscope is able to capture images from different depths in a biofilm.
  • Developments in scientific research follow improvements in apparatus: a deeper understanding of the structure of biofilms is now possible because of improvements to apparatus.

Figure 13.2.3b – Laser scan of biofilmFigure 13.2.3b – Laser scan of biofilm
Confocal laser scan of biofilm development on surfaces with varying porosity. (Source: Gouping Feng et al. Bacterial attachment and biofilm formation. Retrieved: www.nature.com/articles/npjbiofilms201522)

Skill: Evaluating evidence for problems caused by biofilms

All of the bacteria shown in Figure 13.2.3b are species that cause infection in humans.

1. Outline the relationship between surface porosity and biofilm depth for all species.

As the porosity of the surface increases, the depth of the biofilm increases. Positive correlation.

2. Predict which species is a common contaminant of food production surfaces.

  • S. epidermis – forms the thickest biofilms of all species, even on the smoothest surface.

or

  • L. monocytogenes – forms thick biofilms on some surfaces and is not part of the normal human flora (whereas S. epidermis / S. aureus are normally found on skin and in nasal cavities).

NB: the command term 'predict' requires a reason. Answers that mention antibiotic-resistance are not appropriate.

Figure 13.2.3c – Ballast waterFigure 13.2.3c – Ballast water
Ballast tanks transfer potentially harmful biofilms around the world

Figure 13.2.3d – Surgical toolsFigure 13.2.3d – Surgical tools

Did you know?

Biofilms of virulent strains of  Staphylococcus that form on medical equipment and tools are responsible for the majority of infections acquired in hospitals.

Figure 13.2.3e – Overview sewageFigure 13.2.3e – Overview sewage
A typical water treatment facility

Figure 13.2.3f – CLIMFigure 13.2.3f – CLIM
The confocal laser scanning microscope has allowed researchers a deeper understanding of the structure of biofilms.

TOK

Emergent properties are the outcome of the interaction of the elements of a system. In what context is a reductionist approach to science productive and in what context is this approach problematic?