Phenotypic memory in Anthrax spores

Sindhuri Upadrasta

In a new study, researchers from the University of Delhi have shown how spores of the Anthrax bacteria store information in the form of a phenotypic memory”. This information ensures that when the conditions are favourable, the spores grow into robust, infectious agents.

Transmission electron micrograph of Bacillus anthracis
Transmission electron micrograph of Bacillus anthracis  (Photo: Richa Virmani)

Many bacteria can survive unfavorable conditions by developing into spores. These spores, like plant seeds, can remain in a dormant stage for years before getting reactivated. For the bacterium that causes the deadly disease Anthrax, the spore stage is critical for disease transmission. Now, researchers led by Yogendra Singh, Department of Zoology, University of Delhi, have shed light on the molecular pathways that allow Anthrax spores to re-activate when they enter the body of a host.

Anthrax is caused by a bacterium called Bacillus anthracis. This disease mainly affects animals but humans can get infected by inhaling the spores of the bacteria or by coming in contact with diseased animals. Dormant spores of B. anthracis are naturally found in the soil and get activated upon entering the body of the host. The activated bacteria multiply rapidly and spread through the body producing toxins. Spores are the only form of transfer of the disease and have been a subject of research for a long time.

The process by which a spore returns to an activated state on encountering favourable conditions is known as germination. Germination requires a set of cellular components that are deposited in the spore by the original cell that gave rise to it. This is known as phenotypic memory. Phenotypic memory is a relatively new concept and researchers have just started to understand it with respect to bacteria,” says Gunjan Arora, Post-Doctoral fellow at the National Institute of Health, USA, and one of the authors of the story.

While working on B.anthracis, the research team was surprised to find that the bacterial spore has a metabolic enzyme, enolase, carried over from the original cells that formed the spores. Enolase is one of the key enzymes which help the cell generate energy.

The researchers studied the levels of this enzyme at various stages of the bacteria’s life cycle. They found that the enzyme was expressed at high levels during the vegetative (activated) stage, but had reduced expression during the dormant spore stage. To test the role of enolase in the spore, the authors overexpressed this enzyme in the bacteria, which resulted in a ~75% decrease in spore germination.

Once the role of Enolase was clear, we tried to identify the regulators of this enzyme,” says Richa Virmani, the first author of the study. The researchers found that PrkC, a major cellular signaling agent and a known regulator of spore germination, regulates enolase by phosphorylating it. Phosphorylation of Enolase by PrkC helps the germination process by maintaining enolase quantity, localization, and its enzymatic activity. All of these, in turn, have an effect on the viability of the spores,” says Virmani.

Ulf Gerth, senior scientist at the University Of Greifswald, Germany, who was not associated with this research, considers this work to be an important contribution towards understanding the B. anthracis germination process. He says, This work describes a substantial role of enolase in spore germination, whose expression and protein activity is in turn influenced by the PrkC.”

This is the very first report which told the world that there is existence of PrkC mediated regulation of enolase activity, which ultimately leads to the imprinting of overall physiological memory of the spores in B .anthracis,” says Yusuf Akhter, Assistant professor at the Babasaheb Bhimrao Ambedkar University, Lucknow, who was not associated with this study.

Live or attenuated spores have been proposed for usage in vaccination against anthrax for a long time. Studies conducted on the anthrax vaccine have shown the presence of enolase, which has also been suggested to improve the effectiveness of the vaccine.

Our study not only shows the fine regulation of Enolase by PrkC but also proves that enolase is present on the surface of the spores and could help in the design of a live attenuated anthrax spore vaccine,” says Arora.

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