A Film of Bacteria

What am I looking at?

This is a composite image of multiple macro photographic images; it shows the structure of a biofilm created by Pseudomonas aeruginosa bacteria. The bacteria were treated with a dye called Congo red, which stains the extracellular matrix that links the bacteria together in a biofilm.

Biology in the background

Bacteria have an ability to communicate that’s impressive considering that they’re single-celled organisms. They use a process called quorum sensing to detect when other bacteria are near and to initiate cooperative behaviors within the group. This communication happens chemically, with each bacterium secreting specific signals to alert others to its presence. This is the first step in cooperative behaviors, in which groups of bacteria work together.

One of these behaviors is forming a biofilm. A biofilm is created when bacteria secrete long polymers that link individual bacteria to each other, creating an interconnected film, or coating, on all kinds of surfaces. Biofilms are common on your teeth – in a form that we call dental plaque – especially if you don’t brush often. In addition, biofilms can form in the lungs or intestines and in wounds. While brushing your teeth often rids your mouth of the bacteria that create biofilms there, it’s much harder to get rid of bacterial biofilms in the rest of the body, where they can cause serious illnesses.

A single bacterium in this composite image is about 1.5 micrometers long, or roughly 50 times smaller than the width of a human hair. However, an entire biofilm can grow up to a centimeter across (about half the width of a human thumbnail) or even larger in some cases.

Technique

This image was created using macrophotography.