BY : K. Sai Manogna (MSIWM014)

The microbial ecology research covers subjects ranging from individual cells to complex structures and includes several different types of microbes. In studying pure cultures and unique microbial ecosystems, there is not only a visual difference, but there is a difference in the approach of analysis in each of these images.

Fig: Soil bacterium showing multiple flagella in SEM

Fig : Fruiting bodies of various molds.

Studies by scientists from many different research fields discussing ecosystems around the globe have benefited from microbial ecology. The great interest lies in understanding the structure of microbial communities in the ecosystem at this period. It is essential to classify microbes present to attain this understanding; this can be done by using molecular methods even if the microbes have not been cultivated in the laboratory. Microorganisms’ enzymatic processes and microbial adaptations to the environment contribute to our understanding of microorganisms’ physiological ecology.

Roots of Microbial Ecology:

For millennia and long before bacteria were identified, people from various regions around the world used selective procedures to control the production of desired foods.

1. To make fermented milk, starter cultures were passed within a population, and traditional processes were used for fruit juice fermentation.

2. For food preservation, pickling processes involving natural fermentations are customary.

3. Increased rice production has resulted from unique practises in different regions of the world that we now understand are chosen for the growth of nitrogen-fixing cyanobacteria.

4. Some claim that microbiology began in 1675 with the reports by Anton van Leeuwenhoek (1632-1723) describing “very tiny animalcules” in the form of bacteria, yeast, and protozoa.

5. Saliva, dental plaque, and polluted water were the conditions that van Leeuwenhoek investigated.

6. As scientists in different countries studied the environment through direct observations or experimentation, knowledge of microorganisms gradually emerged.

7. Scientists’ contributions to disproving the “spontaneous generation theory” had a significant influence on microbiology, and the presentation by Louis Pasteur at the Sorbonne in Paris in 1864 was particularly important.

8. Pasteur emphasised the significance of microorganisms in fermentation by studying the function of microorganisms in diseases and their effect on our lives.

9. Many consider that Sergei Winogradsky and Martinus Beijerinck were the pioneers of microbial ecology, they were the first people to demonstrate the role of bacteria in nutrient cycles and to formulate concepts of soil microbial interactions.

10. Beijerinck invented the enrichment culture technique to isolate many bacterial cultures, including those now known as Azotobacter, Rhizobium, Desulfovibrio, and Lactobacillus.

11. The early studies of Beijerinck also contributed to the tobacco mosaic virus demonstration and offered insight into virology concepts.

12. Winogradsky was a Russian soil microbiologist who while working with nitrifying bacteria, developed the principle of chemolithotrophy. Winogradsky developed the notion of nitrogen fixation resulting from his experiment with Clostridium pasteurianum, and also demonstrated that bacteria could grow autotrophically with CO2 as the carbon source.

With the prominent interest in microbiology, it became evident that the relationship between microorganisms and also between microorganisms with their environment was highly complex. The study of microbial ecology today covers many different areas.

Current perspectives:

The study of microbial ecology covers the effect of the environment on microbial production and growth. Not only are microorganisms selected for physical and chemical changes in the climate, but biological adaptation helps bacteria and archaea to maximise the use of available nutrients to sustain development.

1. For early life forms, the prokaryotic cell was the ideal device because it had the facility for rapid genetic evolution.

2. Horizontal gene transfer between prokaryotes serves as the mechanism for the cellular evolution of early life forms to generate progeny with different genotypes and phenotypes, as we now understand.

3. While fossils provide evidence of the evolution of plants and animals, they also provide evidence of extinct early animal forms.

4. It is an irony in biology that dinosaurs and other prehistoric forms have engaged in the decomposition of the same prokaryotic organisms that evolved to create eukaryotic organisms. Not only does the prokaryotic mode of life survive today, but it prospers and continues to evolve.

5. It has been calculated that the top one inch of soil has more living microbial cells than several eukaryotic species living above ground.

6. It was estimated by William Whitman and colleagues that there are 5 × 1030 (five million trillion) prokaryotes on earth, and over half of the living protoplasm on earth is made up of these cells.

7. In the human body, the amount of bacteria that develop exceeds the number of human cells by a factor of 10. Although the function of each of these prokaryotic cells cannot be assessed, collectively, groups of prokaryotic cells can have a significant impact on eukaryotic life.

8. Human microbiome analysis shows that although the microbial flora of the skin is identical, each human being has a unique bacterial biome for that individual.

9. Not only are microorganisms involved in nutrient cycling, but they play an essential role in the organisation of the community and interactions with other types of life.

10. Without microorganisms, it would be difficult to imagine life on earth. It is useful to focus on the production of microbes on earth before discussing important divisions in microbial ecology.


The formation of the earth took place around 4.5 billion years ago, followed by the creation of the crust and oceans of the earth.

1. The Earth’s volcanic and hydrothermal activities have emitted different gases into the atmosphere. Dinitrogen (N2), carbon dioxide (CO2), methane (CH4), and ammonia (NH3) were the primary greenhouse gases in addition to water vapour, while hydrogen (H2), carbon monoxide (CO), and cyanide hydrogen (HCN) were present at trace amounts.

2. Scientists have critically examined the chemical discoveries of prebiotic earth that are important to life evolution. The anaerobic climate on earth gave decreasing power for the formation of the first organic compounds.

3. Early life forms were anaerobes that included chemolithotrophs, methanogens, and various microbes using thermophilic H2-showing dissimilar mineral reduction.

4. One of the earliest life forms is suggested to have been hyperthermophilic prokaryotes, and has gathered over 1500 strains of these species from hot terrestrial and submarine environments.

5. There is a significant abundance of these microorganisms in the environment, with 107 Thermoproteus cells found in a gram of boiling mud near active volcanoes, 108 Methanopyrus cells found in a gram of hot chimney rock, and 107 Archaeoglobus and Pyrococcus cells found in deep subterranean fluids below the North Sea per millilitre.

6. Although hyperthermophiles typically grow at 80o-113o C with a pH range of 0-9.0, one archaeal cell, Pyrolobus fumarii, resists in an autoclave with a temperature of 121o C for one hour.

7. Around 90 species of microorganisms are hyperthermophiles at present. The majority of hyperthermophiles are chemolithotrophic species that use molecular hydrogen (H2) as an energy-yielding electron source for reactions.

8. Although S0 is used as an electron acceptor by hyperthermophilic archaea, some hyperthermophiles may combine growth with the use of Fe3+, SO42-, NO3-, CO2 or O2 as electron acceptors.

9. For a few hyperthermophilic archaea, molecular oxygen (O2) is an appropriate electron acceptor and in these situations, only under microaerophilic conditions.

10. To sustain their anaerobic or aerobic growth, hyperthermophilic bacteria typically need organic material. Many anaerobes have active structures that use H2 as the donor of electrons.

The biological synthesis of methane is considered an ancient mechanism and the following reaction would have been attributed to catalysing prokaryotes:

4H2 + CO2 → CH4 + 2H2O

Methanogens might have developed methane from methanol, formate, or acetate if organic compounds such as acetate had accumulated in the environment. Only members of the Archaea domain are capable of the development of methane.

Based on the following reaction, chemoautotrophic microbes may have evolved to expand on energy from molecular hydrogen oxidation and carbon dioxide reduction:

2H2 + CO2 → H2O + [CH2OH]

Ultraviolet radiation may have produced H2 according to the following reaction, in addition to the output of H2 from geological formations:

2Fe2+ + 4H+ → 2H2 + 2Fe3+

The radiolysis of water due to alpha radiation will be another cause of H2. Heterotrophic prokaryotes metabolising organic carbon materials would have emerged sometime after the chemoautotrophs were formed with the accumulation of diverse organic compounds in the ecosystem.

Approximately 3 billion years ago, anaerobic photo-driven energy activities may have been present, using light to cause bacteriorhodopsin-like proteins to pump ions through cell membranes. The bacteriorhodopsin type of photo-driven energetics would have accompanied Chlorophyll-containing anoxygenic bacterial photosynthesis involving purple and green photosynthetic bacteria where H2S was the electron source. Although microbial evolution was initially in the aquatic world, about 2.75 billion years ago, microorganisms may have migrated to dry land. Cyanobacteria formed the aerobic atmosphere with oxygenic photosynthesis, and this was called the “great oxidation case.” Since the photocatalytic process produced O2 from water, the rate of O2 released was not limited by water availability.

Once molecular oxygen was released into the atmosphere, it reacted by microbial and abiotic processes with reduced iron and sulphur compounds (i.e. FeS and FeS2) to create oxidised inorganic compounds. The O2 level in the earth’s atmosphere steadily increased and oxygen respiration may have been used to help the development of the first single-cell eukaryotes by around 1.78-1.68 billion years ago.

The production of ozone (O3) from O2 due to an ultraviolet light reaction was another significant development in the aerobic atmosphere. Ozone absorbs ultraviolet light and forms a protective layer in the atmosphere to shield the earth from ultraviolet radiation’s harmful activities. Microorganisms may have been developing only in subsurface areas or habitats covered by rocks before the creation of the ozone layer.

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