Symbiosis in Saliva

What am I looking at?

This is a cluster of Candida albicans fungus in blue (1) and Streptococcus mutans bacteria in green (2) from a sample of human saliva. You can also see bacteria-derived extracellular polymers known as alpha-glucans in red (3).

Biology in the background

Symbiotic relationships happen throughout the natural world, as well as within our own bodies. An example of symbiosis is the cooperative relationship between some species of shrimp, such as the scarlet cleaner shrimp, and larger fish. These shrimp swim into the mouths of larger fish and eat the food particles that get stuck in their teeth. So the shrimp get a meal and the fish get their teeth cleaned, helping them stay healthy.

These types of cooperative relationships happen in our bodies as well. The bacteria shown in this image are a major player in tooth decay and form complexes with fungi, held together by bacteria-produced polymers. The fungus helps the bacteria move throughout the mouth more quickly, and the bacteria help protect the fungus and enhance its access to food by breaking down sucrose (table sugar) into glucose and fructose, which the fungus can utilize more effectively.

The strands that compose this fungus are about 3 micrometers in diameter, or roughly 25 times smaller than the width of a human hair, but they can reach hundreds of micrometers in length. The bacteria seen here are very small, only about 0.5 micrometers long, or roughly 150 times smaller than the width of a human hair.

Technique

This image was created using confocal microscopy.