Chapter 4 th Microbial Functions in Ecosystems and Global Cycles.pptx

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1. Lecture Notes on Microbial Functions in Ecosystems and Global Cycles Chapter 4 th Microbial Functions in Ecosystems and Global Cycles By Dr.Khawaja Shakeel Ahmed

2. Introduction to Microbes in Ecosystems Microbes are microscopic organisms that include bacteria, fungi, algae, viruses, archaea, and protozoa. Despite their tiny size, they play essential roles in ecosystems by contributing to nutrient cycling, soil health, climate regulation, and overall ecological balance.

3. Microbial Functions in Ecosystems Microbes are crucial for maintaining the functioning of ecosystems. Their roles can be categorized into the following key functions: 1. Decomposition : Microbes break down organic matter (dead plants, animals, and other organic materials) into simpler compounds. This process is vital for recycling nutrients and maintaining soil fertility. Key microbes : Bacteria (e.g., Bacillus , Pseudomonas ) and fungi (e.g., Aspergillus ). Products : Carbon dioxide (CO₂), methane (CH₄), ammonia (NH₃), and other nutrients

4. 2 . Nutrient Cycling : Microbes play a central role in cycling essential nutrients, such as carbon (C), nitrogen (N), sulfur (S), phosphorus (P), and oxygen (O). Examples include: Nitrogen Cycle : Nitrogen-fixing bacteria (e.g., Rhizobium ) convert atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can use. Carbon Cycle : Microbes decompose organic carbon, release CO₂ during respiration, and contribute to the formation of organic carbon in soil. Sulfur Cycle : Sulfate -reducing bacteria play a role in sulfur transformations.

5. 3. Symbiosis and Mutualistic Relationships : Mycorrhizal fungi form symbiotic relationships with plant roots, improving nutrient uptake (especially phosphorus) in exchange for sugars. Nitrogen-fixing bacteria (e.g., Rhizobium in legumes) form mutualistic relationships with plants, converting atmospheric nitrogen into a form the plants can use.

6. 4 . Bioremediation : Microbes are used to degrade environmental pollutants, such as oil spills, heavy metals, and pesticides. This process helps restore polluted environments. For example, Pseudomonas species can degrade hydrocarbons (oil spills).

7. 5. Energy Flow : Microorganisms are central to the food web. They serve as primary producers (photosynthetic microbes) and decomposers (breaking down organic matter). Some microbes, like cyanobacteria , are capable of photosynthesis , contributing to primary production in aquatic ecosystems.

8. Microbial Contributions to Global Biogeochemical Cycles Microbes are involved in several key global cycles that regulate the flow of elements and compounds through ecosystems. 1 Carbon Cycle Microbes play a central role in the carbon cycle by decomposing organic matter, releasing CO₂ into the atmosphere through respiration, and contributing to the formation of organic carbon in soils (as soil organic matter). Key microbes : Bacteria (e.g., Clostridium ), fungi (e.g., Penicillium ), and cyanobacteria. Important processes : Photosynthesis : Cyanobacteria and algae take in CO₂ and release oxygen, providing energy for other organisms. Respiration : Microbes break down organic material, releasing CO₂. Methanogenesis : Certain archaea (e.g., Methanogens ) produce methane (CH₄) in anaerobic conditions, such as in wetlands and the guts of ruminants.

9. 2. Nitrogen Cycle Nitrogen is essential for life as it is a component of amino acids, proteins, and nucleic acids. Microbes drive the nitrogen cycle through several processes: Nitrogen Fixation : Nitrogen-fixing bacteria (e.g., Rhizobium , Azotobacter ) convert atmospheric nitrogen (N₂) into ammonia (NH₃), which can be used by plants. Nitrification : Nitrifying bacteria (e.g., Nitrosomonas ) convert ammonia to nitrites (NO₂⁻) and then to nitrates (NO₃⁻), forms usable by plants. Denitrification : Denitrifying bacteria (e.g., Pseudomonas ) reduce nitrates to nitrogen gas (N₂), releasing it back into the atmosphere.

10. 3. Sulfur Cycle Sulfur is an important component of proteins and coenzymes. The sulfur cycle includes several microbial processes: Sulfur Oxidation : Sulfur bacteria (e.g., Thiobacillus ) oxidize hydrogen sulfide (H₂S) to sulfate (SO₄²⁻), contributing to soil fertility. Sulfate Reduction : Some bacteria (e.g., Desulfovibrio ) reduce sulfate to hydrogen sulfide in anaerobic environments, which can then be used by plants and other organisms.

11. 4. Phosphorus Cycle Phosphorus is vital for DNA, RNA, and energy transfer (ATP). Unlike other cycles, phosphorus has no gaseous phase and primarily cycles through terrestrial and aquatic environments. Phosphate Mineralization : Microbes decompose organic matter, releasing phosphate ions (PO₄³⁻) into the soil. Phosphate Solubilization : Some microbes (e.g., Bacillus , Penicillium ) solubilize insoluble phosphate, making it available to plants. 5 Oxygen Cycle Microbes also play a role in the oxygen cycle. Photosynthetic microbes (e.g., cyanobacteria and algae) produce oxygen as a byproduct of photosynthesis, while many other microbes consume oxygen through cellular respiration.

12. Habitat Characterization and Microbial Ecosystems Microbial habitats can vary greatly, but they share certain features that influence the types of microbes that thrive there. Key factors influencing microbial habitat include: Abiotic Factors : Temperature : Microbes can be classified based on their temperature preferences (e.g., psychrophiles for cold, thermophiles for heat). pH : Some microbes thrive in acidic (acidophiles), neutral (neutrophiles), or alkaline (alkaliphiles) environments. Oxygen Availability : Some microbes are obligate aerobes (require oxygen), obligate anaerobes (cannot tolerate oxygen), while others are facultative anaerobes (can survive with or without oxygen). Moisture and Nutrient Availability : Microbes require water and organic or inorganic nutrients to grow and reproduce. Biotic Factors : Inter-species Interactions : Microbial communities often interact with each other through competition, cooperation (e.g., in biofilms), and parasitism. Symbiotic Relationships : Microbes often form close relationships with larger organisms, such as plants, animals, or other microbes

13. 5. Microbial Communities in Various Habitats Soil Microbes : Soil is home to a vast diversity of microbial life. Microbes in soil help decompose organic material, recycle nutrients, and contribute to soil structure and fertility. Types of soil microbes : Bacteria, fungi, actinomycetes, and algae. Aquatic Microbial Ecosystems : Freshwater and marine ecosystems host diverse microbial communities, which are essential for nutrient cycling and supporting food webs. Phytoplankton (microscopic algae) and bacterioplankton are key primary producers in aquatic ecosystems. Symbioses in Plants and Animals : Microbial communities in the guts of animals (e.g., ruminants like cows) aid in digestion and nutrient absorption. Plant roots form symbiotic relationships with nitrogen-fixing bacteria, improving nitrogen availability. Extreme Environments : Extremophiles are microbes that thrive in extreme conditions such as high salinity (halophiles), high temperature (thermophiles), or high pressure ( barophiles ).

14. Conclusion Microbes are integral to ecosystem health and the functioning of global biogeochemical cycles. They regulate nutrient flow, facilitate energy transfer, and drive the recycling of elements. Understanding microbial processes is essential for managing ecosystems, improving agricultural productivity, mitigating pollution, and tackling environmental challenges.

15. Thank You