Bacterial Spores May Grow on the Frigid Environment of the Icy Moons of Jupiter and Saturn, Could Hold the Key to Finding Extraterrestrial Life

Some microorganisms are susceptible to slight environmental changes, while some have learned to adapt to extreme conditions. For instance, some types of bacteria can retreat into a dormant stage, where they exist as biological spores. This ability is beneficial in cold habitats here on Earth.

What are Bacterial Spores?

Bacterial spore refers to the most dormant form of bacteria which serves as their coping mechanism with harsh environmental conditions. It is a life form that exhibits minimal metabolism, respiration, and reduced enzyme production.

Spores are considered one of the most resilient life forms on Earth. Although they do not replicate or grow, the genetic material of the microorganism is preserved. As the environment becomes favorable for the organism, the spores wake up and return to regular cells. In bacterial species, the spore phase involves a regular bacterial cell forming a tough coat surrounding its genetic material.

Can the Bacterial Spores Thrive on the Icy Moons?

A group of scientists at NASA's Jet Propulsion Lab are challenged by the possibility that bacterial spores may thrive in the frigid subsurface of the icy moons of Jupiter and Saturn. Led by planetary scientist Edith Fayolle, the research team chose a hard Earth microorganism named Bacillus subtilis and studied the behavior of its spores when irradiated by a sun-like light source in the laboratory.

The Bacillus subtilis bacteria is naturally present in almost every part of the Earth, including the human gut. It can turn into a spore when faced with unfavorable environmental conditions. This is why the researchers decided to conduct experiments on it and understand the limits for viability at the cold surface of icy moons.

In this study, Fayolle and her colleagues measured the amount of spores that could be reactivated and be functional again by counting the number of bacterial colonies that grew on the petri dish. It was observed that the spores were more viable after being irradiated at cryogenic temperatures than at room temperatures. In short, they have a greater capacity to wake up and return to a regular cell when exposed to very low temperatures. This is because the low temperatures slowed down the rate of damage brought by radiation.

Is there a possibility that bacterial spores on one of the icy moons could be reactivated? Fayolle believes that the microorganisms in the liquid layers beneath the icy moons could end up on the surface. However, the surfaces of these moons are exposed to solar radiation and charged particles with high energy. This decreases the likelihood that viable microorganisms will thrive on the top surface of the icy world.

When asked about the icy moon best suited for such kinds of spores, Fayolle identified Saturn's moon Enceladus. If there is a chance that microorganisms would form in the sub-surface ocean of Enceladus and make their way to the top surface, the moon's south pole will serve as the environment that will give them the best chance for survival. This region has a lower radiation level and a long winter season. Additionally, icy grains from the outgassing vapor plumes are redeposited and can protect the microorganisms from getting damaged.