MICROBIAL ECOLOGY: HISTORY, OBJECT OF STUDY AND APPLICATIONS - BIOLOGY - 2025

The microbial ecology is a discipline of environmental microbiology arising from the application of ecological principles to microbiology (mikros: small, bios: life, logos: study).

This discipline studies the diversity of microorganisms (microscopic unicellular organisms from 1 to 30 µm), the relationships between them with the rest of living beings and with the environment.

Figure 1. Algae, bacteria and amoeboid protozoa interacting in untreated water samples. Source: CDC / Janice Haney Carr, at: publicdomainfiles.com

Since microorganisms represent the largest terrestrial biomass, their ecological activities and functions profoundly affect all ecosystems.

The early photosynthetic activity of cyanobacteria and the consequent accumulation of oxygen (O ₂) in the primitive atmosphere represents one of the clearest examples of microbial influence in the evolutionary history of life on planet Earth.

This, given that the presence of oxygen in the atmosphere, allowed the appearance and evolution of all existing aerobic life forms.

Figure 2. Cyanobacteria in a spiral shape. Source: flickr.com/photos/hinkelstone/23974806839

Microorganisms maintain a continuous and essential activity for life on Earth. The mechanisms that maintain the microbial diversity of the biosphere are the basis of the dynamics of terrestrial, aquatic and aerial ecosystems.

Given its importance, the possible extinction of microbial communities (due to contamination of their habitats with industrial toxic substances), would generate the disappearance of ecosystems dependent on their functions.

History of microbial ecology

Principles of ecology

In the first half of the 20th century, the principles of general ecology were developed, considering the study of “higher” plants and animals in their natural environment.

Microorganisms and their ecosystem functions were then ignored, despite their great importance in the ecological history of the planet, both because they represent the largest terrestrial biomass and because they are the oldest organisms in the evolutionary history of life on Earth..

At that time, only microorganisms were considered as degraders, mineralizers of organic matter and intermediaries in some nutrient cycles.

Microbiology

Scientists Louis Pasteur and Robert Koch are considered to have founded the discipline of microbiology by developing the technique of axenic microbial culture, which contains a single cell type, descended from a single cell.

Figure 3. Axenic bacterial culture. Source: pixabay.com

However, in axenic cultures the interactions between microbial populations could not be studied. It was necessary to develop methods that would allow the study of microbial biological interactions in their natural habitats (the essence of ecological relationships).

The first microbiologists to examine interactions between microorganisms, in the soil and interactions with plants, were Sergéi Winogradsky and Martinus Beijerinck, while the majority focused on studying axenic cultures of microorganisms related to diseases or fermentation processes of commercial interest.

Winogradsky and Beijerinck studied in particular the microbial biotransformations of inorganic nitrogen and sulfur compounds in the soil.

Microbial ecology

In the early 1960s, in the era of concern for environmental quality and the polluting impact of industrial activities, microbial ecology emerged as a discipline. The American scientist Thomas D. Brock, was the first author of a text on the subject in 1966.

However, it was at the end of the 1970s when microbial ecology was consolidated as a specialized multidisciplinary area, since it depends on other scientific branches, such as ecology, cell and molecular biology, biogeochemistry, among others.

Figure 4. Microbial interactions. Source: Public Health Image Library, at publicdomainfiles.com

The development of microbial ecology is closely related to methodological advances that allow studying the interactions between microorganisms and the biotic and abiotic factors of their environment.

In the 1990s, molecular biology techniques were incorporated into the even in situ study of microbial ecology, offering the possibility of exploring the vast biodiversity existing in the microbial world and also knowing its metabolic activities in environments under extreme conditions.

Figure 5. Microbial interactions. Source. Janice Haney Carr, USCDCP, at: pixnio.com

Subsequently, recombinant DNA technology allowed important advances in the elimination of environmental pollutants, as well as in the control of commercially important pests.

Methods in microbial ecology

Among the methods that have allowed the in situ study of microorganisms and their metabolic activity, there are:

• Confocal laser microscopy.
• Molecular tools such as fluorescent gene probes, which have allowed the study of complex microbial communities.
• The polymerase chain reaction or PCR (for its acronym in English: Polymerase Chain Reaction).
• Radioactive markers and chemical analyzes, which allow measuring microbial metabolic activity, among others.

Sub-disciplines

Microbial ecology is usually divided into sub-disciplines, such as:

• The autoecology or ecology of genetically related populations.
• The ecology of microbial ecosystems, which studies the microbial communities in a particular ecosystem (terrestrial, aerial or aquatic).
• Microbial biogeochemical ecology, which studies biogeochemical processes.
• Ecology of the relations between the host and the microorganisms.
• Microbial ecology applied to environmental contamination problems and in the restoration of ecological balance in intervened systems.

Study areas

Among the areas of study of microbial ecology are:

• Microbial evolution and its physiological diversity, considering the three domains of life; Bacteria, Arquea and Eucaria.
• Reconstruction of microbial phylogenetic relationships.
• Quantitative measurements of the number, biomass and activity of microorganisms in their environment (including non-culturable ones).
• Positive and negative interactions within a microbial population.
• The interactions between different microbial populations (neutralism, commensalism, synergism, mutualism, competition, amensalism, parasitism, and predation).
• Interactions between microorganisms and plants: in the rhizosphere (with nitrogen-fixing microorganisms and mycorrhizal fungi), and in plant aerial structures.
• Phytopathogens; bacterial, fungal and viral.
• Interactions between microorganisms and animals (mutualistic and commensal intestinal symbiosis, predation, among others).
• The composition, functioning and the processes of succession in microbial communities.
• Microbial adaptations to extreme environmental conditions (study of Extremophilic microorganisms).
• The types of microbial habitats (atmosphere-ecosphere, hydro-ecosphere, litho-ecosphere and extreme habitats).
• Biogeochemical cycles influenced by microbial communities (cycles of carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, iron, among others).
• Various biotechnological applications in environmental problems and of economic interest.

Applications

Microorganisms are essential in the global processes that allow the maintenance of environmental and human health. In addition, they serve as a model in the study of numerous population interactions (for example, predation).

The understanding of the fundamental ecology of microorganisms and their effects on the environment has made it possible to identify biotechnological metabolic capacities applicable to different areas of economic interest. Some of these areas are mentioned below:

• Control of biodegradation by corrosive biofilms of metallic structures (such as pipelines, radioactive waste containers, among others).
• Control of pests and pathogens.
• Restoration of agricultural soils degraded by over exploitation.
• Biotreatment of solid waste in composting and landfills.
• Biotreatment of effluents, through wastewater treatment systems (for example, using immobilized biofilms).
• Bioremediation of soils and waters contaminated with inorganic substances (such as heavy metals), or xenobiotic (toxic synthetic products, not generated by natural biosynthetic processes). These xenobiotic compounds include halocarbons, nitroaromatics, polychlorinated biphenyls, dioxins, alkylbenzyl sulfonates, petroleum hydrocarbons, and pesticides.

Figure 6. Environmental contamination with substances of industrial origin. Source: pixabay.com

• Biorecovery of minerals through bioleaching (for example, gold and copper).
• Production of biofuels (ethanol, methane, among other hydrocarbons) and microbial biomass.

References

1. Kim, MB. (2008). Progress in Environmental Microbiology. Myung-Bo Kim Editor. pp 275.
2. Madigan, MT, Martinko, JM, Bender, KS, Buckley, DH Stahl, DA and Brock, T. (2015). Brock biology of microorganisms. 14 ed. Benjamin Cummings. pp 1041.
3. Madsen, EL (2008). Environmental Microbiology: From Genomes to Biogeochemistry. Wiley-Blackwell. pp 490.
4. McKinney, RE (2004). Environmental Pollution Control Microbiology. M. Dekker. pp 453.
5. Prescott, LM (2002). Microbiology. Fifth edition, McGraw-Hill Science / Engineering / Math. pp 1147.
6. Van den Burg, B. (2003). Extremophiles as a source for novel enzymes. Current Opinion in Microbiology, 6 (3), 213–218. doi: 10.1016 / s1369-5274 (03) 00060-2.
7. Wilson, SC, and Jones, KC (1993). Bioremediation of soil contaminated with polynuclear aromatic hydrocarbons (PAHs): A review. Environmental Pollution, 81 (3), 229–249. doi: 10.1016 / 0269-7491 (93) 90206-4.