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Negative Interactions Among Microbial Populations in Soil Microbiology and Their Agricultural Impact

Explores types of negative microbial interactions like amensalism, competition, parasitism, and predation, their mechanisms, roles in soil health, and recent research on microbiome engineering for disease-suppressive soils.

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Submitted By: A. Karthika, II- M.Sc Microbiology, PG and Research Department of Microbiology, Sri Paramakalyani College, Alwarkurichi-627 412 Submitted To: PG and Research Department of Microbiology, Sri Paramakalyani College, Alwarkurichi-627 412 SUBJECT: SOIL MICROBIOLOGY AND MICROBIAL DIVERSITY SUBJECT CODE: 22MBPGCT7 SEMESTER: III TITLE: NEGATIVE INTERACTIONS AMONG MICROBIAL POPULATIONS
CONTENT • INTERACTIONS AMONG MICROBIAL POPULATIONS • TYPES OF MICROBIAL INTERACTION • NEGATIVE INTERACTION  AMENSALISM  COMPETITION  PARASITISM  PREDATION  MECHANISM OF NEGATIVE INTERACTION • RECENT RESEARCH
MICROBIAL INTERACTONS • Biological interactions are the effects that the organisms in a community have on one another. • There are completely different kinds of microbial interactions which incorporates interaction with different microbes, Plant- Germ interactions promoting plant growth, interaction with animals, interaction with humans, and interaction with water, etc. • Microbial interactions are ubiquitous, diverse, critically important in the function of any biological community, and are crucial in global biogeochemistry.
INTERACTIONS AMONG MICROBIAL POPULATIONS • The most common cooperative interactions seen in microbial systems are mutually beneficial. • The interactions between the two populations are classified according to whether both populations and one of them benefit from the associations, or one or both populations are negatively affected.
TYPES OF MICROBIAL INTERATIONS
NEGATIVE INTERACTIONS: AMENSALISM • When one microbial population produces substances that are inhibitory to other microbial population is known as “Amensalism” or “Antagonism”. • The first population which produces inhibitory substances are unaffected or may gain competition and survive in the habitat while other populations get inhibited. This chemical inhibition is known as antibiosis. • Examples of the antagonism (amensalism): • Skin normal flora: Fatty acid produced by skin flora inhibits many pathogenic bacteria in the skin • Thiobacillus thiooxidans: Thiobacillus thioxidans produces sulfuric acid by oxidation of sulfur which is responsible for lowering pH in the culture media which inhibits the growth of most other bacteria.
COMPETITION • The competition represents a negative relationship between two microbial populations in which both the population are adversely affected with respect to their survival and growth. • Competition occurs when both populations use the same resources such as the same space or same nutrition, so, the microbial population achieves lower maximum density or growth rate. • Microbial population competes for any growth-limiting resources such as carbon source, nitrogen source, phosphorus, vitamins, growth factors etc. • Competition inhibits both populations from occupying exactly the same ecological niche because one will win the competition and the other one is eliminated. • Example of competition: • Competition between Paramecium caudatum and Paramecium aurelia: Both species of Paramecium feeds on the same bacteria population when these protozoa are placed together. P. aurelia grow at a better rate than P. caudatum due to competition.
PARASITISM • It is a relationship in which one population (parasite) get benefited and derive its nutrition from other population (host) in the association which is harmed. • The host-parasite relationship is characterized by a relatively long period of contact which may be physical or metabolic. • Some parasite lives outside the host cell, known as ectoparasite while other parasite lives inside the host cell, known as endoparasite. • Examples of parasitism: • Viruses: Viruses are an obligate intracellular parasite that exhibits great host specificity. There are many viruses that are parasite to bacteria (bacteriophage), fungi, algae, protozoa etc. • Bdellovibrio: Bdellavibrio is ectoparasite to many gram-negative bacteria.
PREDATION • It is a widespread phenomenon when one organism (predator) engulf or attack other organisms (prey). • The prey can be larger or smaller than the predator and this normally results in the death of the prey. • Normally predator-prey interaction is of short duration. • Examples of Predation: • a. Protozoan-bacteria in soil: Many protozoans can feed on various bacterial population which helps to maintain the count of soil bacteria at optimum level.
NEGATIVE MICROBIAL INTERACTIONS
MECHANISMS OF NEGATIVE INTERACTIONS MECHANISM EXAMPLE Antibiotic production Streptomyces produces streptomycin - inhibits competing bacteria Bacteriocins Lactobacillus produces lactacin – inhibits closely related bacteria Siderophore-mediated iron competition Pseudomonas produces pyoverdine – captures iron and limits competitors Lytic enzymes Fungi producing chitinase – breaks down the cell wall of competing fungi Volatile Organic Compounds (VOCs) VOCs from Bacillus or Pseudomonas – suppress the competing fungal growth
ROLE IN SOIL HEALTH • Regulation of microbial populations: Competition and antagonism prevent any single microbial species from becoming dominant. • Disease suppression: Beneficial microbes inhibit soil pathogens by producing antibiotics, enzymes, siderophores, and other inhibitory compounds. • Nutrient cycling: Microbial interactions help decompose organic matter and release nutrients such as N, P, and S for plant uptake. • Maintenance of soil biodiversity: Interactions such as competition, predation, and amensalism maintain a diverse and balanced microbial community. AGRICULTURAL IMPORTANCE • Biological control of soil-borne pathogens: Beneficial microbes suppress pathogens through competition, antibiosis, and lytic enzymes. • Suppression of plant diseases: Microbial antagonism reduces the growth and spread of disease-causing organisms. • Improving crop productivity: Reduced disease pressure and better nutrient availability promote healthy plant growth and higher yields. • Sustainable agriculture: Microbial biocontrol reduces dependence on chemical pesticides and supports eco-friendly farming.
RECENT RESEARCH “Microbiome Engineering for Disease – Suppressive Soils” • Marín-Guirao et al. (2025) investigated the role of soil microbial communities in suppressing soil-borne pathogens. o Bacillus, Streptomyces and Trichoderma showed strong antagonistic activity against pathogens. o Biochar, biosolarization, crop rotation and intercropping promoted beneficial microbes. o Increased negative microbial interactions helped suppress soil-borne diseases. o These approaches improved soil health and crop productivity.
REFERENCE • Microbial interaction and its types with examples https://share.google/69ATxjLl0OpiG4Uos • micro-Microbial-Interactionn.pdf https://share.google/1jOYDtSrMEemneH77 • Microbial interaction - Mutualism ,amensalism | PPTX https://share.google/ZmHmWnI2ZcKxUkDOm • Microbiome-based agriculture: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmic b.2025.1677158/full?utm_source=chatgpt.com • Image source – Google and ChatGPT
MORAL STORY THE TWO SEEDS:
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