Heat shock protein protects bacteria from plasma treatment

A heat shock protein protects cells from protein aggregation. It degrades, however, over longer treatment periods.

Plasmas are used, for example, in wound treatment against pathogens that are resistant to antibiotics. However, bacteria can defend themselves: They use a heat shock protein that protects them. A research team led by Professor Julia Bandow and Dr. Tim Dirks from the Chair of Applied Microbiology at Ruhr University Bochum, Germany, showed that bacteria overproducing the heat shock protein Hsp33 can withstand plasma treatment more efficiently than others. The researchers also demonstrated which plasma components activate the heat shock protein. The team published their findings in the Journal of the Royal Society Interface on October 25, 2023.

All bacteria were inactivated after three minutes

When treated with plasma, proteins unfold, lose their natural functions and can clump together. Their accumulation is toxic to cells and can lead to their inactivation. The 33-kDa bacterial heat shock protein, referred to as Hsp33, prevents aggregation by binding unfolded proteins.

To find out whether excess Hsp33 protects cells from plasma, the researchers treated strains overproducing the protein with the plasma source Cinogy, which is already used in dermatology. These strains survived significantly better than wild-type bacteria after a short treatment of about one minute. “After a three-minute treatment, cells producing excess Hsp33 were also deactivated,” Tim Dirks points out.

Heat shock protein activating species

The researchers demonstrated that Hsp33 is activated by plasma by treating the purified heat shock protein with the plasma source. “This activation is related to the oxidation and unfolding of the protein and is actually reversible,” explains Tim Dirks. “However, we also showed that Hsp33 was completely degraded by longer plasma treatment times of one hour.” In addition, the ability of the protein to bind a zinc atom was negatively affected by plasma. This zinc atom reinforces the protein’s natural three-dimensional structure in its inactive state.

Since nothing was previously known about which plasma-produced species can activate Hsp33, the researchers created various stressors known to be produced in plasma and confronted Hsp33 with them one by one.

This showed that Hsp33 is activated by superoxide, singlet oxygen, and atomic oxygen, but is unresponsive to hydroxyl radicals and peroxynitrite.”

Tim Dirks, Chair of Applied Microbiology, Ruhr University Bochum, Germany

This gives an indication of the interaction of these species with bacterial cells. For example, superoxide is one of the first species created by oxidative stress in the body, such as by our immune system in macrophages. A rapid response of Hsp33 to one of these species generated early would therefore be beneficial to the bacterium for rapid protection against oxidative stress. “The superoxide appears to act as a signaling molecule for the bacteria, which further signals oxidative stress,” the research team concludes.