Bacterial Conjugation, Transformation, and Transduction

Posted on Nov 30, 2024 in Biology

A) Conjugation
It is a process by which a donor bacterium transmits DNA through its pili to a recipient bacterium.
Plasmid

The ability to give or receive DNA is a property determined by the presence of episomes, fragments of DNA in donor bacteria that transfer to other bacteria during conjugation.
2) Transformation
It is a process by which bacteria incorporate DNA from the lysis of other bacteria in their surrounding environment. Bacteria capable of capturing environmental DNA are termed competent.

a) Conjugation b) Transduction c) Transformation

3) Transduction
This DNA exchange phenomenon requires a vector: a virus that carries DNA fragments from previously parasitized bacteria.
The phage-carrying bacterial DNA is recombined with the recipient bacterium’s chromosome, creating a new strain.
These phenomena increase bacterial variability and underpin the evolutionary process.

Classification of Bacteria

The types of eubacteria classified by their metabolism are:

a) Autotrophic Eubacteria (capable of producing organic matter)
Phototrophic Eubacteria:

Cyanobacteria: They possess chlorophyll a in cytoplasmic membranous sacs, similar to specialized thylakoid mesosomes. They perform oxygenic photosynthesis (2 photosystems).
Green Bacteria: They contain bacteriochlorophyll in the plasma membrane and attached sacs called chlorosomes. They perform anoxygenic photosynthesis (using compounds without oxygen).
Red Bacteria: They have bacteriochlorophyll in membrane invaginations of varying shapes. They perform anoxygenic photosynthesis. In sulfurous water, sulfur compounds (H₂S) play a key role.

Chemolithoautotrophic Eubacteria:
These bacteria do not use light and obtain energy from the oxidation of inorganic molecules, requiring the presence of oxygen.
This group includes nitrifying bacteria that oxidize soil NH₃ to nitrites and nitrates. Other groups oxidize sulfur to sulfuric acid or ferrous carbonate to ferric hydroxide, fixing CO₂.

b) Heterotrophic Eubacteria
These bacteria use organic substrates, living or dead, as food sources, obtaining nutrients and chemical energy; hence, they are called chemoorganotrophic.
Heterotrophic bacteria can be saprophytic, parasitic, or symbiotic. The largest group, saprophytes, are responsible for decomposition and mineralization of organic remains in ecosystems: fermentation if the substrate is carbohydrate, and putrefaction if the substrate is protein, producing an unpleasant odor and cadaverine.

Archaea

Archaea are a heterogeneous group, phylogenetically distinct from both eubacteria and eukaryotes. Some authors do not consider them bacteria and refer to them as Archaea. Most are anaerobic.
They reproduce by binary division, fragmentation, or budding. They share some molecular features with eukaryotes, such as tRNA introns and similarities in RNA polymerase.
Based on metabolic and ecological properties, they are divided into:

Methanogens: Live in strictly anaerobic environments, producing methane by reducing carbon dioxide with H₂ (swamp gas). Found in environments rich in decaying organic matter, stagnant water, sewage tanks, the digestive tract, hot springs, and the deep ocean.
Extreme Halophiles: Require high salt concentrations, inhabiting reddish, salt-saturated waters like the Red Sea and salt flats.
Thermoacidophiles: Isolated from acidic hot springs, withstanding temperatures above 90°C, such as sulfur geysers. They can live at pH below 2, despite their cytoplasm being near neutral.

Archaea are considered dominant organisms in the primitive biosphere.

Protists

Protists are a diverse group of eukaryotic organisms, primarily unicellular, filamentous, or colonial, except for large algae. They can be:

Oxygenic-photosynthetic: algae or protophytes
Heterotrophic: protozoa

They are aquatic (freshwater or marine) or live in moist environments, like inside plants and animals, acting as parasites or symbionts.
Reproduction can be sexual or asexual, sometimes with complex life cycles.
Many are mobile, moving via undulipodia (cilia or flagella), amoeboid movement, or flexuous motion.

Protozoa

Fungi

Fungi include single-celled organisms (yeasts responsible for industrial fermentation) and multicellular organisms composed of filamentous hyphae, forming the mycelium (mold). They sometimes produce macroscopic reproductive structures: sporophores (mushrooms). They are heterotrophs.
Their cells have rigid chitin-covered walls, and their energy reserve is glycogen.
Asexual reproduction, the most common type, occurs via conidia, asexual spores formed at the end of hyphae called conidiophores. These conidia germinate and form a new vegetative mycelium. Some fungi reproduce sexually.
Based on nutrition, fungi can be:

Saprophytes: Feed on dead organic matter.
Parasites: Mycelium grows on other living organisms, plants, and animals.
Symbionts: Live in close relationships with plants, benefiting both. Examples include lichens (algae perform photosynthesis, and the fungus provides moisture) and mycorrhizae (the plant photosynthesizes, and the fungus absorbs water and minerals).

Fungi are decomposers.

Microorganisms: Biological Interest

Geochemical Activity of Microorganisms
When plant and animal remains are incorporated into the soil, microbial activity begins, digesting and oxidizing organic compounds. Microorganisms also play a role in rock breakdown and topsoil formation. They are actively involved in biogeochemical cycles and act as decomposers in ecosystem food chains.

Cycles of Matter
The recycling of elements in living matter is called the cycle of matter or biogeochemical cycles. While many agents are involved, microorganisms play a major role. The major cycles are:

The carbon cycle
The nitrogen cycle

Microorganisms as Agents of Infectious Diseases

In 1876, Robert Koch studied anthrax, an infectious disease affecting cattle and sheep, transmissible to humans. He inoculated mice with the blood of infected animals, and they contracted the disease and died. His experiments demonstrated that a specific pathogenic bacterial species causes a defined disease. He later described the tuberculosis bacillus and Vibrio cholerae. Pathogenic microorganisms are responsible for certain diseases, invading animals through wounds and natural openings. Some pathogens, called opportunistic microorganisms, only cause disease when the animal’s defenses are weakened.
Key concepts related to infectious diseases:

Infectious Disease: A disease caused by a pathogen.
Infection: The growth of a microorganism within host tissues.
Hypersensitivity Reaction: Abnormal reactions of the host defense system.
Pathogenicity: The ability of a microorganism to produce disease.
Virulent Strain: A strain that causes illness.
Safe Strain: A strain that does not cause disease.
Carrier Individual: Individuals in whom the organism is in the incubation or latent phase, after overcoming the illness.
Quarantine: Contagion time.
Epidemic: Many cases of a disease in a small geographic area.
Pandemic: An infectious disease spread over a wide area of the Earth.
Endemic Disease: Consistently affects a particular community, but its occurrence is not very high.
Toxigenicity: The ability to produce toxins (proteins or polysaccharides) that cause damage in the host.