10- Microorganisms in natural environments

Question 1

Explain the general ecological concepts; ecosystem; habitat

Answer 1

• Ecosystem: The sum of all organisms and abio?c factors in a particular environment. An ecosystem is a dynamic complex of plants, animals, microbial communities and the nonliving surroundings, which interact as a functional unit.

• Habitat: Portion of an ecosystem where a community could reside. Many habitats
are unsuitable for plants and animals, and some habitats are almost exclusively microbial.

• An ecosystem contains many different habitats.
• Microbes account for ~50% of all biomass on Earth. They are ubiquitous on the surface and deep within the earth. Microbes show great metabolic diversity and are the major players in nutrient cycles.

Question 2

Explain the general ecological concepts; population; community; species richness; species abundance

Answer 2

• Population: a group of microorganisms of the same species residing in the same
place at the same time.

• Community: a group of populations.

• The diversity of microbial species in an ecosystem is expressed in two ways:
– Species richness: the total number of different species present
– Species abundance: the proportion of each species in an ecosystem

• Microbial species richness and abundance are a function of the kinds and amounts of nutrients available in a given habitat.

Question 3

Explain the general ecological concepts; guilds; niche; energy inputs

Answer 3

• Guilds: Metabolically
related microbial populations. Sets of guilds form microbial communities that interact with macroorganisms and abiotic factors in the ecosystem.

• Niche: Habitat shared by a
guild. Supplies nutrients as
well as conditions for growth.

• Energy inputs: sunlight,
organic carbon, reduced
inorganic substances.

Question 4

Explain microenvironment

Answer 4

• The growth of microbes depends on resources and growth conditions.
• Difference in the type and quantity of resources and the physiochemical conditions of a habitat define the niche for each microbe.
• For each organism there exists at least one niche in which that organism is most successful (prime niche).

• Microenvironment
– The immediate environmental surroundings of a microbial cell or group of cells
– Soil particles contain many
microenvironments

Question 5

Explain microenvironment; competition; cooperation; relationships

Answer 5

• Physiochemical conditions in a microenvironment are subject to rapid change,
both spatially and temporally.

• Resources in natural environments are highly variable and many microbes in
nature face a feast-or-famine existence (storage is important).

• Growth rates of microbes in nature are usually well below maximum growth rates defined in the laboratory.
• Competition and cooperation occur between microbes in natural systems and between microbes and higher organisms.

• Many microbes establish relationships with other organisms
– Parasitism: one member in the relationship is harmed and the other benefits.
– Mutualism: both species benefit (symbiosis).
– Commensalism: one species benefits and the other is neither harmed nor helped.

Question 6

Explain biogeochemistry

Answer 6

• Biogeochemistry: the study of biologically mediated chemical transformations.

• A biogeochemical cycle defines the transformations of a key elements by biological
and chemical agents.

• Typically proceed by oxidation–reduction reactions
• Microbes play critical roles in energy transformation and biogeochemical processes that result in the recycling of elements to living systems.
– Carbon cycle (CO2 à Organic compounds à CO2)
– Nitrogen cycle (N2 à NH3 à NO2à NO3 à NO2- à NO à N2O à N2)
– Sulfur cycle (H2S à SO42- à H2S)