Environmental
Microbiology
1
,Microbial Communities and Ecosystem
Ecological hierarchy of microorganisms:
Ecosystem
↑
Community
↑
Guild
↑
Population
↑
Individual
Guild: Populations that use the same resources are called guild. They occur within a community. Guilds are defined
according to their locations, attributes or activities of their component species. For example, the mode of acquiring
nutrients, the mobility and the habitat zones that the species occupy or exploit can be used to define a guild.
Community: It is the highest biological unit in an ecological hierarchy made up of individual and populations.
Or Highest biological unit in and ecological hierarchy composed of interacting populations is called community.
Habitat: Populations within a community interact with each other in an integrated manner. They do so at a physical
location called habitat.
Population: A population consists of individuals of the same species that live, interact and migrate through the same
niche and habitat. It is a group/aggregation of related individuals (same species) capable of interbreeding and living
(occupying) a continuous area that contain no potential breeding barrier.
Criteria of population:
1. The organisms are of the same kind.
2. They occupy a particular area.
3. The population is the structural component of an ecosystem which develops and maintains itself by
reproduction i.e., it is a self-regulating system.
4. The basic characteristic of a population is its size or density (numbers per unit area or per unit volume).
Niche: The functional role of an organism within an ecosystem; the combined description of the physical habitat,
functional role and interactions of the microorganisms occurring at a given location is called niche.
Biome: Several interacting communities are called biome.
Population selection within communities:
• r strategies r = rate of increase in population
• k strategies k = carrying capacity of the environment
2
,r strategies
Characteristics:
1. Dominates in resourceful environment
2. Occurs at low population density / uncrowded condition
3. High reproduction rate
4. Unstable environment where change is unpredictable
5. Subject to extreme fluctuations
6. When resources scarce, population crash (i.e. rapid reduction in growth rate). In long inactive period, they
produce spores.
Example: Saccharomyces, Pseudomonas, Archeae, Aspergillus, Bacillus etc.
K strategies:
Characteristics:
1. Dominates in resource limited environment
2. Occurs at high population density
3. Optimal utilization of environmental resources
4. Have physiological adaptations
5. Reproduction rate is slow
6. Usually stable and are permanent members of the community
Example: Soil Streptomyces, Desmids in oligotrophic lakes, Agrobacterium, Basidiomycota.
Differences between r and k strategies:
r strategies k strategies
1. Dominates in resourceful environment. 1. Dominates in resource limited environment.
2. Occurs at low population density/uncrowded 2. Occurs at high population density.
condition.
3. High reproduction rate. 3. Low reproduction rate.
4. Unstable environment where change is 4. Relatively stable environment where change is
unpredictable. predictable.
5. Subject to extreme fluctuations. 5. Usually do not subject to extreme fluctuations.
6. When resources scarce, population crash. 6. Normally resources do not scarce and
population also do not crash.
7. In long inactive period members produce spores. 7. There is no long inactive period and no
production of spores.
8. Do not have physiological adaptations. 8. Have physiological adaptations.
9. Example: Saccharomyces, Pseudomonas, 9. Example: Soil Streptomyces, Desmids in
Archeae, Aspergillus, Bacillus etc. oligotrophic lakes, Agrobacterium,
Basidiomycota.
Succession within microbial communities
Succession: It is the process of orderly, sequential change in the species structure in a community over time. Succession
may be of primary and secondary.
Primary succession: Colonization of a virgin habitat is called primary succession. The first colonizers are known as
pioneer organisms. All pioneer organisms must be able to reach the virgin environment, so a common feature of pioneer
microorganisms is effective dispersal mechanisms. Primary succession alters environment which discourage further
succession.
Example: The gastrointestinal tract of newborn animals.
3
, Secondary succession: When succession occurs in a habitat with a previous colonization and succession history, it is
called secondary succession. It is the consequence of some catastrophic event that has disrupted and altered the course
of primary succession.
Preemptive colonization: It occurs by secondary invaders, when pioneers alter the condition of the habitat. They may
extend the regions of pioneers or replace them.
Climax community: After the invasion of secondary invaders, habitat undergoes additional changes and succession
ends with a stable assemblage of populations called the climax community.
Autotrophic succession: When gross production (P) exceeds the rate of community respiration (R), organic matter
accumulates. (In many ecosystems, production is equivalent to photosynthesis, but in some, such as deep - sea
hydrothermal vent communities, production is the result of chemolithotrophic metabolism).
𝑃
Autotrophic succession occurs in cases where is initially greater than 1. As long as P is greater than R, biomass will
𝑅
𝑃
accumulate during the autotrophic succession. As the ratio approaches 1, succession toward a stable community is
𝑅
occurring.
Example: Terrestrial cyanobacteria, Lichens.
Properties:
1. An autotrophic succession of microorganisms occurs in environments largely devoid of organic matter when
there is a non-limiting supply of solar energy.
2. Autotrophic succession occurs in young pioneer communities, such as on newly exposed volcanic rock.
3. In autotrophic succession within a mineral environment, such as on bare rock, the photosynthetic pioneer
organisms have minimal nutritional requirements and high tolerance to adverse environmental conditions.
4. The ability to use atmospheric nitrogen is an advantage of this type of succession. Terrestrial cyanobacteria
and lichens are good examples of pioneers in this type of environment.
𝑃
Heterotrophic succession: Heterotrophic succession occurs in cases where is less than 1, because consumption is
𝑅
greater than production. Succession in such a situation is called heterotrophic succession.
Example: Gut community.
Characteristics:
1. In heterotrophic succession, the energy flow through the system decreases with time, there is insufficient
organic matter input, and the community gradually uses its stored chemical energy.
2. Heterotrophic succession is usually temporary, because it culminates in the extinction in the community when
the stored energy supply is exhausted.
3. Many microbial communities involved in decompositional processes exhibit such temporary heterotrophic
succession. For example, the microbial communities on a fallen log disappear after the log is completely
decomposed.
4. It is possible for heterotrophic succession to lead to a stable community if there is a continuous source of
allochthonous organic matter (i.e. organic matter from an external source).
5. Pioneers in a heterotrophic succession need to have above all, high metabolic and growth rates in order to stay
ahead of secondary invaders.
Differences between autotrophic and heterotrophic succession:
Autotrophic succession Heterotrophic succession
1. When gross production (P) exceeds the rate of 1. When rate of community respiration (R)
community respiration (R) and succession exceeds gross production (P) and succession
occurs, it is called autotrophic succession. occurs, it is called heterotrophic succession.
2. Autotrophic succession occurs in cases where
𝑃 2. Heterotrophic succession occurs in cases where
𝑅 𝑃
> 1. < 1.
𝑅
3. It occurs in environments when there is a non- 3. It occurs in environments when there is a limited
limiting supply of solar energy. supply of solar energy.
4. It is usually not temporary. 4. It is usually temporary.
4
Microbiology
1
,Microbial Communities and Ecosystem
Ecological hierarchy of microorganisms:
Ecosystem
↑
Community
↑
Guild
↑
Population
↑
Individual
Guild: Populations that use the same resources are called guild. They occur within a community. Guilds are defined
according to their locations, attributes or activities of their component species. For example, the mode of acquiring
nutrients, the mobility and the habitat zones that the species occupy or exploit can be used to define a guild.
Community: It is the highest biological unit in an ecological hierarchy made up of individual and populations.
Or Highest biological unit in and ecological hierarchy composed of interacting populations is called community.
Habitat: Populations within a community interact with each other in an integrated manner. They do so at a physical
location called habitat.
Population: A population consists of individuals of the same species that live, interact and migrate through the same
niche and habitat. It is a group/aggregation of related individuals (same species) capable of interbreeding and living
(occupying) a continuous area that contain no potential breeding barrier.
Criteria of population:
1. The organisms are of the same kind.
2. They occupy a particular area.
3. The population is the structural component of an ecosystem which develops and maintains itself by
reproduction i.e., it is a self-regulating system.
4. The basic characteristic of a population is its size or density (numbers per unit area or per unit volume).
Niche: The functional role of an organism within an ecosystem; the combined description of the physical habitat,
functional role and interactions of the microorganisms occurring at a given location is called niche.
Biome: Several interacting communities are called biome.
Population selection within communities:
• r strategies r = rate of increase in population
• k strategies k = carrying capacity of the environment
2
,r strategies
Characteristics:
1. Dominates in resourceful environment
2. Occurs at low population density / uncrowded condition
3. High reproduction rate
4. Unstable environment where change is unpredictable
5. Subject to extreme fluctuations
6. When resources scarce, population crash (i.e. rapid reduction in growth rate). In long inactive period, they
produce spores.
Example: Saccharomyces, Pseudomonas, Archeae, Aspergillus, Bacillus etc.
K strategies:
Characteristics:
1. Dominates in resource limited environment
2. Occurs at high population density
3. Optimal utilization of environmental resources
4. Have physiological adaptations
5. Reproduction rate is slow
6. Usually stable and are permanent members of the community
Example: Soil Streptomyces, Desmids in oligotrophic lakes, Agrobacterium, Basidiomycota.
Differences between r and k strategies:
r strategies k strategies
1. Dominates in resourceful environment. 1. Dominates in resource limited environment.
2. Occurs at low population density/uncrowded 2. Occurs at high population density.
condition.
3. High reproduction rate. 3. Low reproduction rate.
4. Unstable environment where change is 4. Relatively stable environment where change is
unpredictable. predictable.
5. Subject to extreme fluctuations. 5. Usually do not subject to extreme fluctuations.
6. When resources scarce, population crash. 6. Normally resources do not scarce and
population also do not crash.
7. In long inactive period members produce spores. 7. There is no long inactive period and no
production of spores.
8. Do not have physiological adaptations. 8. Have physiological adaptations.
9. Example: Saccharomyces, Pseudomonas, 9. Example: Soil Streptomyces, Desmids in
Archeae, Aspergillus, Bacillus etc. oligotrophic lakes, Agrobacterium,
Basidiomycota.
Succession within microbial communities
Succession: It is the process of orderly, sequential change in the species structure in a community over time. Succession
may be of primary and secondary.
Primary succession: Colonization of a virgin habitat is called primary succession. The first colonizers are known as
pioneer organisms. All pioneer organisms must be able to reach the virgin environment, so a common feature of pioneer
microorganisms is effective dispersal mechanisms. Primary succession alters environment which discourage further
succession.
Example: The gastrointestinal tract of newborn animals.
3
, Secondary succession: When succession occurs in a habitat with a previous colonization and succession history, it is
called secondary succession. It is the consequence of some catastrophic event that has disrupted and altered the course
of primary succession.
Preemptive colonization: It occurs by secondary invaders, when pioneers alter the condition of the habitat. They may
extend the regions of pioneers or replace them.
Climax community: After the invasion of secondary invaders, habitat undergoes additional changes and succession
ends with a stable assemblage of populations called the climax community.
Autotrophic succession: When gross production (P) exceeds the rate of community respiration (R), organic matter
accumulates. (In many ecosystems, production is equivalent to photosynthesis, but in some, such as deep - sea
hydrothermal vent communities, production is the result of chemolithotrophic metabolism).
𝑃
Autotrophic succession occurs in cases where is initially greater than 1. As long as P is greater than R, biomass will
𝑅
𝑃
accumulate during the autotrophic succession. As the ratio approaches 1, succession toward a stable community is
𝑅
occurring.
Example: Terrestrial cyanobacteria, Lichens.
Properties:
1. An autotrophic succession of microorganisms occurs in environments largely devoid of organic matter when
there is a non-limiting supply of solar energy.
2. Autotrophic succession occurs in young pioneer communities, such as on newly exposed volcanic rock.
3. In autotrophic succession within a mineral environment, such as on bare rock, the photosynthetic pioneer
organisms have minimal nutritional requirements and high tolerance to adverse environmental conditions.
4. The ability to use atmospheric nitrogen is an advantage of this type of succession. Terrestrial cyanobacteria
and lichens are good examples of pioneers in this type of environment.
𝑃
Heterotrophic succession: Heterotrophic succession occurs in cases where is less than 1, because consumption is
𝑅
greater than production. Succession in such a situation is called heterotrophic succession.
Example: Gut community.
Characteristics:
1. In heterotrophic succession, the energy flow through the system decreases with time, there is insufficient
organic matter input, and the community gradually uses its stored chemical energy.
2. Heterotrophic succession is usually temporary, because it culminates in the extinction in the community when
the stored energy supply is exhausted.
3. Many microbial communities involved in decompositional processes exhibit such temporary heterotrophic
succession. For example, the microbial communities on a fallen log disappear after the log is completely
decomposed.
4. It is possible for heterotrophic succession to lead to a stable community if there is a continuous source of
allochthonous organic matter (i.e. organic matter from an external source).
5. Pioneers in a heterotrophic succession need to have above all, high metabolic and growth rates in order to stay
ahead of secondary invaders.
Differences between autotrophic and heterotrophic succession:
Autotrophic succession Heterotrophic succession
1. When gross production (P) exceeds the rate of 1. When rate of community respiration (R)
community respiration (R) and succession exceeds gross production (P) and succession
occurs, it is called autotrophic succession. occurs, it is called heterotrophic succession.
2. Autotrophic succession occurs in cases where
𝑃 2. Heterotrophic succession occurs in cases where
𝑅 𝑃
> 1. < 1.
𝑅
3. It occurs in environments when there is a non- 3. It occurs in environments when there is a limited
limiting supply of solar energy. supply of solar energy.
4. It is usually not temporary. 4. It is usually temporary.
4
