Engineers Unveil Survival Mechanisms of a Singularly Durable Life Form, the Spore

Bacterial spores are some of nature’s most adept survivors. Subject to extreme environments – blazing and freezing temperatures, drought and even the vacuum of space – they coat themselves in a thick husk and lie dormant until conditions improve.

In studying the way these single-cell organisms respond to an environmental change – an uptick in humidity, Gennady Gor, an associate professor of chemical and materials engineering at New Jersey Institute of Technology, noticed anomalous behaviors.

“They swell significantly and quickly. One of their amazing properties is just how fast they respond, faster even than hydrogels. They also retract quickly when humidity declines,” he said. “This is not typical of most materials. I believe it’s related to their mechanisms for survival.”

Gor noted that spores’ outer structure, which is composed of peptidoglycan, a polysaccharide, behaves similarly to rubber with respect to its swelling, elasticity and relaxation times.

Earlier experimental work suggested that moisture enters pores in these layers, expanding them. His research, however, pointed to a different swelling mechanism: water penetrating between the flexible molecular chains of the peptidoglycan, pushing them apart, as it does it does in hydrated polymer networks such as hydrogels. He compared the process to combining spaghetti with sauce, noting “there are no pores in spores.”

The structure of hydrogels and peptidoglycan is similar in that both are composed of cross-linked molecular chains. With collaborators at Princeton University, Gor published these findings in the journal Proceedings of the National Academy of Sciences.

“There is a lot to be learned about what natural materials are capable of doing,” noted Howard Stone, the Donald R. Dixon '69 and Elizabeth W. Dixon Professor in Mechanical and Aerospace Engineering at Princeton and a co-author of the paper. “Getting more insights is valuable, especially in drawing analogies with other similar materials.”

From a materials science perspective, understanding the physical properties of spores may help in creating nature-inspired materials with similar characteristics. For example, since their response to humidity is fast and reversible, the materials that comprise spores may be promising materials for actuators, which convert energy into mechanical forces such as movement and are used in many types of machines.

Gor added, “If we understand the unique materials properties of peptidoglycan, we may better understand how bacterial spores survive harsh conditions, and figure out how to kill the spores of pathogenic bacteria, such as anthrax.”

In his Laboratory for Materials Interfaces, he focuses on nanoporous materials, solids with pores of 100 nanometers and below. Such materials play a significant role in both nature and technology. Synthetic varieties, for example, are widely used in the chemical industry as adsorbents, catalysts and separation membranes, among other uses. He conducts simulations of these materials at a molecular scale in order to predict their behavior, such as how they absorb water, hydrocarbons and other fluids.

 “Kids’ dinosaur eggs swell, but it takes hours. If the kinetics of the process can be improved, one can utilize such materials for energy harvesting, or as sensors,”Gor said.

He’s also interested in what happens at the interfaces of different phases, such as solids and liquids and how molecules interact with the surface of pores. He noted, “This can help us determine the best molecular structures for capturing CO2 or designing gas masks and protective clothing.”