A probe of the human microbiome has uncovered a wealth of novel and potentially useful bacterial proteins.

Biological surveys often overlook ‘small’ proteins of 50 or fewer amino acids. To probe this unexplored realm, Ami Bhatt at Stanford University in California and her colleagues used computational tools to identify small proteins that are made by the microbes in human skin, vaginas, guts and mouths.

The researchers found more than 400,000 molecules that fell into roughly 4,500 ‘families’, or groups that contain candidate proteins with similar compositions and lengths. Less than 5% of these proteins had been identified before.

The team’s haul includes ‘housekeeping’ proteins that are essential for cellular function. Some of these proteins are highly abundant, but had still escaped notice. Other proteins might protect bacteria from toxins that the bacteria use to kill viruses.

Small proteins could have applications in medicine or biotechnology, the authors say.