3.1D: Microbial Environments and Microenvironments

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The extraordinary biological diversity among microbes reflects their ability to occupy every habitable environment on the planet.

Learning Objectives

Define microenvironments

Key Points

Microorganisms are found in practically every habitat present on the planet.
Microorganisms have evolved to survive in extraordinarily diverse environments, including extreme, hostile, or otherwise intolerant ecological systems.
In addition to occupying a unique niche within an ecosystem, microbes adapt to microenvironments (or microhabitats) that can be distinguished from the immediate surroundings by such factors as the amount of incident light, the degree of moisture, and the range of temperatures.

Key Terms

microenvironment: The very small environment in the immediate vicinity of an organism.
extremophilic: Of or pertaining to the extremophiles, a class of organism that thrives under extreme conditions of temperature, salinity, and so on; commercially important as a source of enzymes that operate under similar conditions.
ubiquitous: Being everywhere at once: omnipresent.

Microorganisms are found on practically every habitable square inch of the planet. They live and thrive in all parts of the biosphere where there is liquid water, including hostile environments such as the poles, deserts, geysers, rocks, and the deep sea. Additionally, while microbes are often free-living, many have intimate symbiotic relationships with other larger organisms. Clearly, microbes have adapted to extreme and intolerant conditions, and it is this adaptation that has yielded tremendous biological diversity among microorganisms.

Like all extant organisms, microbes have evolved to thrive within a given environmental context. Microorganisms are ubiquitous despite the fact that the planet is host to extraordinarily diverse environments. Therefore, microbes have adapted to fill every ecological niche on the planet. For example, extremophilic species have been found that can tolerate the following environmental extremes:

Temperatures as high as 130 °C (266 °F) and as low as −17 °C (1 °F)
Highly alkaline (pH 0) and highly acidic (pH 11.5) environments
Extremely saline environments (including those in which the salt concentration is saturating)
Extremely high (1,000-2,000 atm) and low (0 atm) pressures (some bacteria can survive for prolonged periods in a pressure-less vacuum, meaning they might even survive in space)
High ionizing radiation (up to 15,000 Gy; as a reference, a mere 5 Gy would kill a human! )

These evolutionary adaptations have allowed microbial life to extend into much of the Earth’s atmosphere, crust, and hydrosphere (the water found over, under, and on the surface of a planet).

In addition to occupying a unique niche within an ecosystem, microbes are potentially sensitive to subtle environmental differences between adjacent areas. These differences define so-called microenvironments (or microhabitats) that can be distinguished from the immediate surroundings by such factors as the amount of incident light, the degree of moisture, and the range of temperatures. For example, the side of a tree that is shaded from sunlight is a microenvironment that typically supports a somewhat different community of microorganisms than would be found on the side that receives regular light. Microbes, therefore, are not only adapted to their habitat, but also to the immediate environment, thus promoting increased diversity among microbial species within an ecosystem.