Comprehensive Overview of Single Microbial Population Dynamics in Soil Microbiology

Comprehensive Overview of Single Microbial Population Dynamics in Soil Microbiology

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  SUBJECT: SOIL MICROBIOLOGY& MICROBIAL ECOLOGY SUBJECT CODE: 22MBPGT7 TOPIC: SINGLE MICROBIAL POPULATION SUBMITTED BY: A.DAISY BEULA 25081236511712102 II MSC MICROBIOLOGY SRI PARAMAKALYANI COLLEGE, ALWARKURUCHI SUBMITTED TO: PG AND RESEARCH DEPARTMENT OF MICROBIOLOGY SRI PARAMAKALYANI COLLEGE, ALWARKURUCHI
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  CONTENT  Introduction Characteristics • Quorum sensing • Cooperation • Competition • Biofilm formation • Resource sharing • Genetic exchange • Population density regulation
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  Introduction A single microbialpopulation is a group of microorganisms belonging to the same species that live in a common habitat, share similar genetic and physiological characteristics, grow and reproduce together, and interact with one another to ensure survival and adaptation.
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  Characteristics 1. Same Species:All microorganisms belong to the same species or strain and share common characteristics. 2. Genetic Similarity: Members have similar genetic makeup, with only minor variations due to mutations. 3. Habitat: They live in the same environment and experience similar physical and chemical conditions. 4. Uniform Growth Pattern: The population exhibits similar growth, metabolism, and reproduction under favorable conditions. 5. Similar Environmental Response: The microorganisms respond similarly to changes in temperature, pH, nutrients, oxygen, and moisture.
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  Growth kinetics –Growth curve Lag Phase – Cells adapt to the new environment, synthesize enzymes, and prepare for cell division. There is little or no increase in cell number. Log (Exponential) Phase – Cells divide rapidly at a constant rate, and the population doubles at regular intervals. This is the period of maximum growth. Stationary Phase – The rate of cell division equals the rate of cell death due to nutrient depletion and accumulation of waste products. The total population remains relatively constant. Death (Decline) Phase – Cells die faster than new cells are formed, causing a gradual decrease in the number of viable microorganisms.
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  1. Cell-to-Cell Communication Quorumsensing is a communication mechanism in which bacteria produce, release, and detect chemical signaling molecules (autoinducers). When the bacterial population reaches a certain density, these signaling molecules accumulate and trigger coordinated gene expression. Functions: Biofilm formation EPS production Virulence factor production Sporulation Nitrogen fixation regulation Example Rhizobium releases signaling molecules while colonizing legume roots. When enough bacteria are present, they coordinate root nodule formation and nitrogen fixation.
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  2. Cooperation Cooperation occurswhen microorganisms of the same species help one another, resulting in mutual benefit. How Cooperation Occurs: Sharing extracellular enzymes Sharing nutrients Producing protective substances Coordinated movement Joint biofilm formation Example: Pseudomonas aeruginosa communicate through quorum sensing and cooperate to produce extracellular enzymes and biofilms, allowing the entire population to obtain nutrients efficiently.
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  3. Competition Competition occurswhen microorganisms compete with members of the same species for limited resources. Types of Competition a) Competition for Nutrients When nutrients become limited, cells compete for available food sources. Example: Carbon source, nitrogen, phosphorus. b) Competition for Oxygen Aerobic bacteria compete for dissolved oxygen. Example: Bacillus species in liquid culture. C) Competition for Space Microorganisms compete for attachment sites on surfaces. Example: Root surface colonization by Rhizobium.
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  4. Biofilm Formation Biofilmis a community of microorganisms attached to a surface and surrounded by a protective layer called EPS (Extracellular Polymeric Substances). Biofilms help microorganisms survive under harsh conditions. Biofilm Formation Step: Step 1: Initial attachment to a surface. Step 2: Irreversible attachment. Step 3: EPS production. Step 4: Microcolony formation. Step 5: Mature biofilm development. Step 6: Dispersion of cells. Example: Rhizobium forms a biofilm on the surface of legume roots by producing EPS. This helps the bacteria attach firmly to the roots and promotes root nodule formation for nitrogen fixation.
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  5. Resource Sharing Resourcesharing is the process in which some microorganisms produce and release useful substances into the environment that benefit other members of the same microbial population. This cooperation improves the survival and growth of the entire population. Function: Digest complex nutrients Improve iron uptake Protect neighboring cells Increase community survival Example: Bacillus subtilis secretes extracellular enzymes that break down starch into simple sugars, which can be used by all nearby Bacillus cells.
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  6. Genetic Exchange Althoughmembers belong to the same species, they may exchange genetic material. Types: Transformation: Uptake of free DNA from surroundings. Conjugation: DNA transfer through a pilus. Transduction: DNA transfer by bacteriophages.
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  7. Population DensityRegulation The microbial population regulates its growth according to nutrient availability. When nutrients are abundant, bacteria divide rapidly. As nutrients decrease and waste accumulates, growth slows and the population enters the stationary phase. Example An E. Coli culture in a nutrient broth grows rapidly during the log phase. As nutrients become depleted, growth slows and the culture enters the stationary phase.
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  Reference 1. Madigan, M.T.,Bender, K.S., Buckley, D.H., Sattley, W.M., & Stahl, D.A. (2021). Brock Biology of Microorganisms (16th ed.). 2. Google scholar: Rachel J Whitaker, Jillian F Banfield Trends in Ecology & Evolution 21 (9), 508-516, 2006 3. Online source: science direct & SlideShare
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  Thank You!