CASE STUDIES OF CLIMATE CHANGE EFFECTS ON MICROBIAL COMMUNITIES

Introduction           

In this study, we wanted to know if there are effects of climate change on microbial communities. As we know, microorganisms can live in any ecosystem regardless of habitat conditions; they are really flexible and able to adapt under adverse conditions. The competition in areas with little biological availability of resources is very high, for this reason, the microorganisms have different adaptations that make them gain an advantage over others. Therefore, these adaptations represent an evolution for their survival. The greenhouse effects are changing the natural habitats of these microorganisms, because bacteria can adapt and survive. This fact indicates that they may be able to survive under conditions of climate change.

Microorganisms and microbiological mechanisms

Influence of climate change on communities of microorganisms

Global warming is associated with carbon dioxide (CO₂) emissions, the result of the burning of fossil fuels or the abundant aerobic respiration of our planet. However, there are other gases whose impact on the greenhouse effect is much more important than CO₂. One of them is methane (CH₄), a product of the metabolism of certain microorganisms in digestion, from some organic matter in the absence of oxygen. Another is nitrous oxide (NO₂), which releases bacteria from the soil when there is an excess of nitrogen fertilizers in the environment. These are clear examples of the intervention of microorganisms in the emission of greenhouse gases.

The increase in these greenhouse gas emissions over the past 150 years, resulting from human activities, is leading to major changes in the climate. These changes are altering the functioning and composition of ecosystems and the goods and services they provide.

However, since climate models have not taken into account the role of microorganisms, both in the capture of CO2 and in the production of methane or nitrous oxide, their predictive capacity is reduced. This is why the development of molecular techniques, which help us to know biodiversity, and even the abundance of certain microorganisms in any ecosystem, is essential to understand the fate of the planet and possibly change its course through some strategies to reduce greenhouse gas emissions.

The image below represents the direct and indirect effects of climate change, such as high CO₂ or N deposition, and alteration of temperature or precipitation. It can be observed how a feedback is made to the atmosphere or to the growth of the plant.

Although we do not know with certainty the consequences of climate change in microbial communities, it has been estimated that the increase in temperature can move the epidemiological range of several diseases associated with warmer climates. Likewise, the surface of the oceans, just by increasing their temperature by a couple of degrees, becomes a great breeding ground for the formation of bacterial communities, including some dangerous species such as Vibrio, which is responsible for food poisoning, gastroenteritis and cholera. Also some cyanobacteria, a type of photosynthetic bacteria releasing toxins that affect human health, causing damage to the nervous system, dermatitis or allergic reactions.

The effect of climate change on the microbial communities of glaciers

Global warming is also producing important changes in the microbial communities of the Arctic and Antarctica. Glaciers have been successfully colonized by numerous microorganisms, including representatives of bacteria, archaea, unicellular eukaryotes and viruses. These communities are the most important microorganisms in the polar areas because they accumulate the greatest diversity of life known there, and cover large ice-free areas during polar summers.

The increase in temperature is causing an increase in toxin-producing cyanobacteria, which destroy microorganism communities in polar areas. The effects of these toxins are lethal to the organisms that inhabit these microecosystems, such as viruses, bacteria, protozoa, fungi, nematode worms, among others, that feed on cyanobacteria and play a crucial role in the global biogeochemical cycles of the planet.

These microorganisms are highly vulnerable to climate change and are especially adapted to extreme environments. This characteristic makes them favorable for adaptation and speciation. Therefore, the consequences of climate change on these microbial communities can have important repercussions on the functioning of different areas of the planet, and therefore on the regulation of the terrestrial climate.

Can small microorganisms provide large situations?

There are two clear examples, shown in Figure 2, of how these tiny microorganisms help us combat climate change. One of them is certain planktonic microorganisms, which are found on the surface of the oceans. They intervene in the regulation of the Earth's temperature by releasing an organic compound into the air, dimethyl sulfide, hereafter called DMS, which is also responsible for the characteristic smell of the sea.

In the atmosphere, ultraviolet (UV) radiation breaks down the DMS, forming aerosols that accumulate in the clouds, which prevent radiation from reaching the Earth's surface. The decrease in atmospheric temperature, caused by this event, drops to -3 or -4 º C.

Dimethylsulfonium propionate (DMSP) is found in plankton's unicellular algae, a compound used by algae as an osmotic regulator against salt in seawater. When algae die, they release the DMSP, which is used by bacteria for energy and nutrients.

The residue from this process is the DMS that goes into the atmosphere only if the marine ecosystem is healthy. When there is an excess of organic matter, for example, that which comes from the waters of a river contaminated by waste such as fertilizers, industrial waste or fecal water, dead zones are generated where large quantities of CO₂ are produced and DMS is not released.

On the other hand, in response to methane production, there are methanotrophic bacteria, which consume methane naturally and are abundant in many ecosystems, including the surface of leaves. Undoubtedly, if these bacteria did not exist, the methane present on the bottom of the ocean and in the marshes would come to the surface, producing immediate climate change. This effect would probably be far greater than that caused by human activity over a century ago.

Conclusion

There are many physicochemical parameters that affect the growth and activity of microorganisms, such as: temperature, Oxygen and Red-Ox potential, pH, water activity, osmotic pressure, salinity, hydrostatic pressure, irradiance and nutrients. Bacterial growth is achieved through a chemical process in which temperature is the strongest parameter, nutrients are also related to all types of bacteria. The other parameters are more related to spaces and their metabolism, such as the presence of oxygen in respiration. Global warming has great consequences on temperature, so the communities of microorganisms will be influenced by it at different levels. Depending on the species, the impact will be positive, increasing the number of colonies of microorganisms, or causing a negative denaturation of proteins.

Also climatic persecution and pollution help the reproduction of microorganisms, for example, the presence of nitrates in water favors the reproduction of microorganisms. These contaminations provide essential elements for bacteria, which use nitrates to obtain energy, eliminating the limit of energy for growth.

Climate change affects microbial colonies. This affectation can be good or bad, creating great problems for the habitat in general. Also the incredible capacity of evolution of the microorganisms, makes them easily adaptable to the greenhouse effect.

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