Climate change and the secret of hidden life in extreme environments

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Introduction

Climate change is a phenomenon caused by the combustion of fossil fuels such as oil, coal, and natural gas, resulting in the emission of greenhouse gases into the atmosphere. Exposure to extremely high or low temperatures causes stresses that are sometimes lethal to living cells. However, microorganisms in nature are very different from each other. Some of them can live happily in environments considered as “extreme” due to environmental conditions that would not allow the survival of many other species, even evolutionarily superior.

A clear example of this phenomenon is the discovery made by some researchers of the Foundation Edmund Mach (F.E.M.), with the University of Tuscia, the Joint Genome Institute and the University of California, who identified in Antarctica (Fig. 1) 269 new species of bacteria belonging to the class of Actinobacteria (also called Actinomycetes), Chloroflexi and Proteobacteria.

Figure 1 - Antarctica territory – [Credit: Focus.it]
Figure 1 – Antarctica territory – [Credit: Focus.it]

How do microorganisms manage to survive for thousands of years in extreme environments such as frozen ground?

According to Beat Frey, a researcher at the Federal Research Institute “WSL”, some microorganisms living in the permafrost have a metabolism that can be very active even at low temperatures and very particular cell structures that are difficult to find in other living beings. In particular, to use the scarce nutrient sources of the frozen soil, these organisms produce proteases, lipases, α-amylases and exploit an over-regulation of their natural biodegradative operons. An experiment related to over-regulation was performed by a direct assay of urocanase and histidase activity in wild-type cells of various Antarctic psychotropic strains, including P. syringae, P. fluorescens, and P. putida. The assay showed high expression of the hut operon at low temperatures. Additionally, other studies on mutants showed distinct genetic differences associated with the insertion in the gene for urocanase (hutU) of the histidine utilization operon (hut).

As observed, some species can activate their metabolism even under particular conditions while others remain dormant for long periods. The resumption of metabolic activity occurs in particular conditions determined, for example, by global warming. The last findings associated with dormancy date back to 2005, when some NASA scientists have been able to isolate, in Alaska, some bacteria dating back to 32.000 years ago while in Siberian tundra have been isolated, some “giant viruses” survived for 30.000 years. To understand the size of these prehistoric viruses is possible to consider the Mollivirus sibericum (Fig. 2) that has about 500 genes against, for example, the 8 genes possessed by influenza A virus.

Figure 2 – Giant virus: Mollivirus sibericum – [Credit: repubblica.it]
Figure 2 – Giant virus: Mollivirus sibericum – [Credit: repubblica.it]

Climate change and dormant species

The melting of ice occurs at a speed that man can hardly control. The major concern is the possible rise of the oceans and the consequent climatic changes around the globe, but not less important is the possibility of reawakening pathogens trapped in the ice. Consequently, it is thought that new or already eradicated diseases could be “dormant” and buried under thick layers of ice.

For this reason, some studies have been focused on the Arctic ice (Fig. 3). Researchers identified eight genes that confer the ability to survive and resist aminoglycoside, β-lactam, and tetracycline antibiotics naturally produced by microorganisms. Among these resistance genes, four also conferred resistance to a modern semi-synthetic antibiotic called amikacin that is not naturally possessed by currently known organisms.

Figure 3 – Artic ocean map – [Credit: ercantastorie.com]
Figure 3 – Artic ocean map – [Credit: ercantastorie.com]

Can reactivation of dormant microorganisms be dangerous to humans?

The problem of global warming could lead to the reactivation of some forms of life that are currently trapped in the ice spread across the globe. Unfortunately, there is no clear and certain answer to this question: all the theories are gathered in a great unknown. The main doubts revolve around the possible existence of many viruses still unknown, perhaps pathogenic, preserved in the old permafrost layers. However, microorganisms must not be only and necessarily harmful. Therefore, it’s possible to trust in discovering non-pathogenic life forms useful in the medical field and biotechnological development.

The potential hidden inside the ice

Psychotolerant bacteria can adapt to living at low temperatures by several strategies and were isolated at 7 °C from Arctic soil. These were differentiated from each other by analysis of the substrates that these were able to oxidize. In addition, 16s RNA sequence analyses revealed that most belonged to the genus Pseudomonas. The observations obtained from the studies by Master et al. suggested the presence of particular characteristics that allow these spectacular microorganisms to survive – a different composition of the cell membrane, the regulation of some genes and the modification of enzymes to act with great efficiency at low temperatures.

Cold-adapted enzymes are defined by their relative thermolability, greater flexibility, and higher activity at low temperatures than their mesophilic and thermophilic counterparts. The enzyme systems detected in the isolated species were essentially useful for the degradation of polychlorinated biphenyls (PCBs, Fig. 4).

Figure 4 – Polychlorinated biphenyls (PCB) chemical structure – [Credit: biomonitoring.ca.gov]
Figure 4 – Polychlorinated biphenyls (PCB) chemical structure – [Credit: biomonitoring.ca.gov]

Therefore, according to this investigation, it is possible to think about the possible use of bacteria still hidden inside the ices to remediate some environments through new bioremediation strategies then the use of microorganisms to reduce the environmental concentration of compounds such as PCB.

Conclusions

There is no reliable way to calculate the probability of other life forms in environments where it is already difficult to assume the survival of any living being. Still, research in this direction has innumerable evolutionary and biological implications. For example, detecting microscopic species unusually adapted to cold represents an important step to reconsider and re-evaluate the mechanisms that regulate the cycle of carbon and nutrients in the global ecosystem, understand the evolution of proteins, and develop new biotechnologies design new protocols for bioremediation.

Gennaro Velotto

References

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