Environmental Microbiology GATE

Prokaryotic and Eukaryotic Microorganisms

Prokaryotic Microorganisms:

1. Cell Structure: Prokaryotes lack a true nucleus and membrane-bound organelles. Their genetic material is found in a single, circular DNA molecule in the nucleoid region.
2. Size: Generally smaller in size, with a diameter ranging from about 0.5 to 5 micrometers.
3. Reproduction: Reproduce asexually through processes like binary fission, where the parent cell divides into two identical daughter cells.
4. Organelles: Lack membrane-bound organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus.
5. Ribosomes: Smaller ribosomes (70S) compared to eukaryotic cells (80S).
6. Cell Wall: Present in many prokaryotes, with diverse compositions. For instance, bacteria have cell walls containing peptidoglycan.
7. Examples: Bacteria and archaea are the two main domains of prokaryotic microorganisms.

Eukaryotic Microorganisms:

1. Cell Structure: Eukaryotic microorganisms have a true nucleus, which houses their genetic material, and membrane-bound organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus.
2. Size: Typically larger than prokaryotic cells, with diameters ranging from a few micrometers to several millimeters.
3. Reproduction: Eukaryotes reproduce both sexually and asexually, depending on the species. Sexual reproduction involves the fusion of gametes (sex cells) to form offspring.
4. Organelles: Possess various membrane-bound organelles that carry out specialized functions within the cell.
5. Ribosomes: Larger ribosomes (80S) compared to prokaryotic cells (70S).
6. Cell Wall: Some eukaryotic microorganisms, such as fungi and plant cells, have cell walls. Fungal cell walls are composed of chitin, while plant cell walls are primarily made of cellulose.
7. Examples: Fungi, protists (e.g., amoebas, algae), and some microscopic forms of plants and animals are eukaryotic microorganisms.

Characteristics of Diverse Groups of Microorganisms

Bacteria:

• Cell Type: Prokaryotic
• Shapes: Varied shapes including cocci (spherical), bacilli (rod-shaped), and spirilla (spiral)
• Metabolic Diversity: Some bacteria can photosynthesize, while others are heterotrophic
• Roles: Participate in nutrient cycling, some are pathogens causing diseases

Archaea:

• Cell Type: Prokaryotic
• Extreme Environments: Many are extremophiles, thriving in extreme conditions like high temperatures, acidity, or salinity
• Biochemistry: Differ from bacteria and often have unique metabolic pathways

Fungi:

• Cell Type: Eukaryotic
• Cell Wall: Made of chitin
• Feeding: Heterotrophic, absorb nutrients from their environment
• Forms: Include yeasts (unicellular) and molds (multicellular)

Protists:

• Cell Type: Eukaryotic
• Diversity: Unicellular to simple multicellular forms
• Lifestyles: Range from photosynthetic algae to parasitic forms

Classification of Microorganisms

Microorganisms are classified into several taxonomic groups:

Domain:

• Bacteria
• Archaea
• Eukarya (includes all eukaryotic microorganisms)

Kingdoms (Eukarya):

• Protista (for unicellular eukaryotes like protists)
• Fungi (for fungi including yeasts and molds)
• Plantae (for plant-like microorganisms such as algae)
• Animalia (for microscopic animals)

Additional Classification Levels:

• Phylum
• Class
• Order
• Family
• Genus
• Species

Microorganisms are organized into these hierarchical categories based on their evolutionary relationships and shared characteristics.

Microbial Diversity

Microbial diversity refers to the incredible variety of microorganisms that exist on Earth. These microorganisms are found in virtually every habitat, from the depths of oceans to the most extreme environments. The diversity of microorganisms is observed in their:

Genetic Diversity:

Microbes have diverse genetic material, allowing them to adapt to various conditions and carry out unique functions.

Metabolic Diversity:

Microorganisms exhibit a wide range of metabolic processes, including photosynthesis, chemosynthesis, and various forms of nutrient uptake.

Ecological Roles:

Microbes play essential roles in ecosystems, such as nutrient cycling, decomposition, and symbiotic relationships.

Adaptations:

Microbes have evolved specific adaptations to thrive in extreme environments, including high temperatures, acidity, and high pressure.

Applications:

Microbial diversity has led to applications in biotechnology, medicine, and environmental management, including bioremediation and biofuel production.

Unexplored Diversity:

Despite advances in research, much of microbial diversity remains unexplored, with many species yet to be discovered and characterized.

Studying microbial diversity provides insights into the fundamental processes of life and the potential for harnessing microorganisms for various beneficial purposes.

Plant-Microbe and Soil-Microbe Interactions

Plant-Microbe Interactions:

Microbes and plants engage in various interactions that have profound impacts on both parties:

Symbiotic Relationships:

• Mycorrhizal Associations: Beneficial fungi called mycorrhizae form symbiotic relationships with plant roots, enhancing nutrient uptake, especially phosphorus.
• Nitrogen-Fixing Bacteria: Certain bacteria convert atmospheric nitrogen into a form plants can use, benefiting both the plants and the microbes.

Disease and Defense:

• Pathogens: Some microbes are plant pathogens, causing diseases that can impact agricultural productivity.
• Plant Defense: Plants have evolved mechanisms to recognize and defend against pathogens, often involving complex interactions with beneficial microbes.

Soil-Microbe Interactions:

Soil is a complex ecosystem where microorganisms play crucial roles:

Nutrient Cycling:

Microbes decompose organic matter, releasing nutrients that plants can use for growth. This process supports the biogeochemical cycling of elements like carbon and nitrogen.

Bioremediation:

Some microbes have the ability to degrade pollutants in soil, contributing to the cleanup of contaminated environments.

Soil Structure:

Microbial activities influence soil structure and aggregation, which affects water retention, aeration, and nutrient availability for plants.

The interactions between plants, microbes, and soil are complex and crucial for ecosystem health and stability.

Role of Microorganisms in Wastewater Treatment

Microorganisms play a vital role in the process of wastewater treatment, helping to remove contaminants and pollutants from water before it's released back into the environment:

Biological Treatment Processes:

Microorganisms are used in various biological treatment methods:

Activated Sludge Process:

Microbes in activated sludge tanks break down organic matter in wastewater through aerobic digestion, producing biomass flocs that settle out.

Trickling Filters and Rotating Biological Contactors (RBCs):

Microbes form biofilms on media, where they degrade organic matter as wastewater trickles over them.

Sequencing Batch Reactors (SBRs):

Microorganisms treat wastewater in batches, with alternating periods of aeration and settling.

Nutrient Removal:

Microbes play a role in removing nutrients, like nitrogen and phosphorus, from wastewater:

Nitrification:

Ammonia is converted to nitrate through the activity of nitrifying bacteria.

Denitrification:

Denitrifying bacteria convert nitrate to nitrogen gas, reducing nitrogen levels in wastewater.

Sludge Treatment:

Microorganisms are also involved in the treatment of sludge produced during wastewater treatment:

Anaerobic Digestion:

Microbes break down organic matter in sludge in the absence of oxygen, producing biogas and stabilizing the material.

Aerobic Digestion:

Microorganisms degrade remaining organic matter in sludge under aerobic conditions.

Microbial communities in wastewater treatment systems perform essential roles in breaking down pollutants and facilitating the purification of water for safe release into the environment.

Bioremediation and Biogeochemical Cycling

Bioremediation:

Bioremediation is the use of microorganisms to clean up pollutants and contaminants from the environment:

Microbial Degradation:

Microbes are used to break down organic pollutants in soil, water, and air into simpler, less harmful compounds.

Oil Spill Cleanup:

Oil-degrading bacteria can help mitigate the environmental impact of oil spills by breaking down hydrocarbons.

Biogeochemical Cycling:

Biogeochemical cycles involve the movement of elements through living organisms and the environment:

Carbon Cycle:

Microbes play key roles in carbon cycling, both as producers (photosynthetic bacteria and algae) and decomposers (bacteria and fungi).

Nitrogen Cycle:

Nitrogen-fixing bacteria convert atmospheric nitrogen into a form usable by plants, while other microbes facilitate nitrification and denitrification processes.

Sulfur Cycle:

Microbes mediate the conversion of sulfur compounds, releasing sulfur dioxide and hydrogen sulfide into the atmosphere.

Phosphorus Cycle:

Microorganisms aid in the cycling of phosphorus by breaking down organic matter and releasing phosphate ions for plant uptake.

Microbes are essential drivers of biogeochemical cycles, shaping the movement and availability of elements in ecosystems.

Bioremediation and Biogeochemical Cycling

Bioremediation

Aspect	Explanation
Microbial Degradation	Microorganisms break down organic pollutants in soil, water, and air into simpler, less harmful compounds.
Oil Spill Cleanup	Oil-degrading bacteria help mitigate environmental impact by breaking down hydrocarbons in oil spills.

Biogeochemical Cycling

Element	Microbial Role
Carbon Cycle	Microbes act as producers (photosynthetic bacteria and algae) and decomposers (bacteria and fungi) in the cycle.
Nitrogen Cycle	Nitrogen-fixing bacteria convert atmospheric nitrogen into plant-usable forms, while others facilitate nitrification and denitrification.
Sulfur Cycle	Microbes mediate the conversion of sulfur compounds, releasing sulfur dioxide and hydrogen sulfide into the atmosphere.
Phosphorus Cycle	Microorganisms break down organic matter and release phosphate ions for plant uptake in the cycle.