Microbial Population and Community Dynamics

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Questions and Answers

What does species richness refer to in a microbial community?

The proportion of each species in the community

The environmental conditions impacting microbial growth

The genetic diversity within a single species

The total number of different species present (correct)

How does nutrient availability affect species abundance in microbial habitats?

More nutrients lead to lower species abundance

Nutrient scarcity encourages high species abundance

Nutrient abundance can result in dominance by a few species (correct)

Nutrient levels do not impact species abundance

What is typically observed in organic-rich soils regarding species richness?

High species richness with most species at moderate abundance (correct)

Low species richness with few dominant species

A constant number of species regardless of conditions

Uniform abundance across all species

What term describes the tiny local environment that microorganisms experience?

Microenvironment Signup and view all the answers

How do extreme environments typically affect microbial species richness?

They often result in very low species richness but may have high abundance of a few species Signup and view all the answers

What effect do the metabolic activities of a microbial community have on its habitat?

They can modify the physicochemical conditions of the habitat Signup and view all the answers

What is the typical challenge microorganisms face in their natural ecosystems?

An intermittent supply of resources leading to feast-or-famine conditions Signup and view all the answers

In terms of microbial community structure, what is species abundance?

The proportion of each species in the community Signup and view all the answers

What is the primary reason for microorganisms to produce storage polymers?

To serve as reserve materials when resources are abundant or scarce Signup and view all the answers

What factor influences the competition among microorganisms in a habitat?

Rate of nutrient uptake Signup and view all the answers

What is syntrophy in the context of microbial interactions?

Cooperation between different microbes to achieve transformations they can't perform alone Signup and view all the answers

How do surfaces impact microbial habitats?

They offer greater protection from environmental disturbances Signup and view all the answers

How does the growth rate of microorganisms in nature typically compare to laboratory conditions?

It is usually lower due to suboptimal conditions Signup and view all the answers

What is a characteristic of planktonic cells compared to surface-associated cells?

They exist in a floating state with less nutrient access Signup and view all the answers

What role do surfaces play in microbial accumulation?

They provide a substrate for cell attachment and resource modification Signup and view all the answers

In which environment can microbial accumulation on a surface reach significant thickness?

Hot springs lacking small animal grazers Signup and view all the answers

What is the primary characteristic of a mutualistic relationship?

Both members are metabolically dependent on each other. Signup and view all the answers

Which of the following is NOT an example of a mutualistic relationship?

Microbial populations causing secondary infections. Signup and view all the answers

In a mutualistic relationship, how does the benefit to each partner influence their survival?

It allows them to inhabit environments they couldn't occupy alone. Signup and view all the answers

Which of the following organism associations is identified as a type of mycorrhizae?

Ectomycorrhizae with tree roots. Signup and view all the answers

What is the primary difference between ectoparasites and endoparasites?

Ectoparasites live outside the host, while endoparasites live inside. Signup and view all the answers

What distinguishes commensalism from mutualism?

One partner benefits while the other remains unaffected in commensalism. Signup and view all the answers

How do microbial populations, like those of Mycobacterium leprae, influence other species in commensal interactions?

They create new entry points for unrelated microbial populations. Signup and view all the answers

Which type of parasitism involves a fungus making contact with a host and excreting toxic substances?

Necrotrophic mycoparasitism Signup and view all the answers

What characteristic feature distinguishes viruses as parasites?

They exhibit great host specificity and are obligate intracellular parasites. Signup and view all the answers

Which organism is NOT typically considered a benefactor in a mutualistic relationship?

Pathogenic bacteria causing disease. Signup and view all the answers

What is the main purpose of predation in a biological context?

To regulate population levels of prey organisms. Signup and view all the answers

What role does the dominant partner play in lichen symbiosis?

It provides most characteristics of the lichen. Signup and view all the answers

Which statement about Bdellovibrio is accurate?

Bdellovibrio acts as an ectoparasite by penetrating the outer membrane of its bacterial host. Signup and view all the answers

What distinguishes proto-cooperation from mutualism?

The association is beneficial but not obligatory. Signup and view all the answers

In syntrophism, what is a crucial aspect of the interaction between two microorganisms?

The growth of one organism improves due to the substrate from another. Signup and view all the answers

Which of the following examples illustrates proto-cooperation?

Desulfovibrio provides hydrogen sulphide to Chromatium. Signup and view all the answers

What is the primary benefit organisms gain from syntrophic interactions?

Improved metabolic functions collectively achieved. Signup and view all the answers

Which metabolic process is dependent on interspecies hydrogen transfer in a methanogenic ecosystem?

Methane production by methanogenic bacteria. Signup and view all the answers

How do Lactobacillus arobinosus and Enterococcus faecalis support each other's growth?

They produce essential amino acids for one another. Signup and view all the answers

What is the role of fermentative bacteria in a syntrophic relationship with methanogenic bacteria?

They generate CO2 and H2 for methanogenic bacteria. Signup and view all the answers

In proto-cooperation, what type of products do the interacting microbial populations create?

Cellular material more than they could alone. Signup and view all the answers

Study Notes

Microbial Population vs Community

Microbial population: One species living in association with others
Microbial community: Consists of multiple microbial populations

Key Factors Influencing Microbial Species Richness and Abundance

Species richness: Total number of different species present
Species Abundance: Proportion of each species in the community
Habitat conditions: Factors like available nutrients and prevailing conditions directly impact richness and abundance

Microbial Habitats

Microorganisms thrive in diverse environments including common habitats like soil and water, extreme environments, and on/within other organisms.
Each environment has defined physicochemical conditions shaped by the microbial community’s metabolic activities

Microenvironments

Microbes experience a limited local environment called their microenvironment.
Microenvironments can change rapidly within a single habitat.

Microbial Nutrient Levels & Growth Rates

Microorganisms often face a “feast-or-famine” existence.
Extended periods of exponential growth are rare in nature.
Growth rates are usually lower than laboratory maximum rates.

Microbial Competition & Cooperation

Competition for resources is intense with factors like nutrient uptake rate, metabolic rates, and growth rates impacting the outcome.
Syntrophy: Microbes working together in metabolic transformations that are not possible individually.
Examples of complementary metabolisms: Nitrifying bacteria and archaea.

Microbial Surfaces

Surfaces provide important habitats offering:
- Greater nutrient access
- Protection from predation and environmental disturbances
- A way for cells to remain in favorable habitats, modify them, and avoid being washed away.
Flow across a surface increases nutrient transport.
Surfaces can be provided by other organisms or by nutrients like organic matter particles.

Surface Colonization

Can be sparse, with microcolonies invisible to the naked eye.
Can be so dense, that microbial accumulation is visible.
Thickness can reach centimeters in extreme environments without grazing animals.

Mutualism (Positive Interaction)

Mutualism is an obligatory relationship where both organisms benefit metabolically.
Mutualists are specifically dependent on each other, and cannot be replaced by other species.
Physical contact between organisms is required.
Allows organisms to thrive in habitats they could not occupy alone.
They act as a single organism.

Mutualism Examples

Rhizobium-legume association: Nitrogen fixation.
Mycorrhizae: Symbiosis between plant roots and fungal hyphae.
- Ectomycorrhizae, Endoomycorrhizae, and Ectendomycorrhizae.
Lichens: Symbiosis between a fungus and alga.
- Fungus (mycobiont) is the dominant partner.
- Alga (phycobiont) can be cyanobacteria.
Herbivore-microbial interactions: Intestinal bacteria in ruminants.
- Ruminococcus flavefaciens, Ruminococcus albus, and Fibrobacter succinogenes.

Commensalism (Positive Interaction)

Commensalism is a unidirectional relationship where one organism benefits, and the other is unaffected.
Examples:
- Disease-causing microbes opening lesions for other microbes.
- Staphylococcus: Some species are commensal skin flora, while others cause infections.
- Aspergillus: Lives in the gastrointestinal tract and can cause aspergillosis in immunocompromised individuals.

Proto-cooperation (Synergism) (Positive Interaction)

Both populations benefit from each other.
Allows for metabolic activities, with nutrient exchange between species.
Association is NOT obligatory.
Example 1: Desulfovibrio bacteria and Chromatium bacteria.
- Desulfovibrio supplies hydrogen sulfide and carbon dioxide.
- Chromatium provides sulfates and organic material.
Example 2: Azotobacter and Cellulomonas.
- Azotobacter fixes nitrogen.
- Cellulomonas provides glucose.

Syntrophism (Positive Interaction)

Special symbiosis between two metabolically different microorganisms.
Cooperation through short-distance metabolite transfer.
Both organisms can carry out a metabolic function that neither can alone
The growth of one organism depends on or is improved by another's substrate.
Example: Methanogenic ecosystem in sludge digester.
- Methanogenic bacteria produce methane using hydrogen transferred from fermentative bacteria.
- Anaerobic fermentative bacteria utilize carbohydrates for CO2 and H2, which Methanobacter uses for methane production.
Example: Lactobacillus arobinosus and Enterococcus faecalis
- E.faecalis requires folic acid from L.arobinosus.
- L.arobinosus requires phenylalanine from E.faecalis

Parasitism (Negative Interaction)

Characterized by a long-term physical or metabolic contact between host and parasite.
Ectoparasites live outside the host cell, while endoparasites live inside.
Examples:
- Fungi: Mycoparasitism (necrotrophic, biotrophic)
- Viruses: Obligate intracellular parasites with host specificity (bacteriophage, fungi, algae, protozoa).
- Bdellovibrio: Ectoparasite to gram-negative bacteria.
  - Penetrates the host's outer membrane, entering the periplasmic space (not the cytoplasm).

Predation (Negative Interaction)

One organism (predator) engulfs or attacks another (prey), resulting in the prey's death.
Short-duration interactions.
Examples:
- Protozoa-Bacteria in soil: Protozoa feed on bacteria.
- Predatory bacteria: Bdellovibrio, Vampirococcus, Daptobacter.

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Description

This quiz explores key concepts related to microbial populations and communities, including factors influencing species richness and abundance. Understand how microorganisms adapt to diverse habitats and examine the importance of microenvironments in their growth. Test your knowledge on microbial dynamics in various environments.