It's a mouldy old world we live in. Every day we inhale tiny particles of the mould Aspergillus just like these, magnified 20,000 times under an electron microscope. While it doesn't cause problems for most people, Aspergillus can lead to serious or even life-threatening fungal infections (known as aspergillosis) in those with weak immune systems. But while there are many different species of Aspergillus growing in the environment, one of them – Aspergillus fumigatus (top) – causes 80 per cent of infections, while others – such as Aspergillus nidulans (bottom) hardly ever cause disease. The difference comes down to a sugary molecule on the surface of the fungus cells. Infectious Aspergillus nidulans particles are thickly covered in the stuff (arrowed), making them more resistant to the fungus-fighting powers of the immune system. Other species have much less of it, so they're quickly cleared away before an infection can take hold.
Written by Kat Arney
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.