Microbiology MCQs with Answer and Explnation | Chapter 5

Answer: Both Castaneda & Machiavello stains and Giminez stains

Ziehl-Neelsen stain is used to stain acid-fast bacteria, such as Mycobacterium tuberculosis and Mycobacterium leprae. Chlamydiae are not acid-fast bacteria, so they do not stain well with Ziehl-Neelsen stain.

Gimenez stain and Castaneda & Machiavello stains are both silver-based stains that are used to stain Chlamydiae. These stains bind to the DNA in the Chlamydiae cell, which gives them a characteristic red or pink color.

Gimenez stain is more commonly used than Castaneda & Machiavello stains. It is a simpler and more reliable stain, and it can be used to stain Chlamydiae in both cell culture and clinical specimens.

Answer: Elementary bodies and Reticulate bodies

Chlamydiae have a biphasic life cycle involving two distinct forms: elementary bodies (EBs) and reticulate bodies (RBs).

Elementary bodies (EBs) are the infectious, metabolically inert form of Chlamydiae. They are smaller, denser, and more durable, allowing them to survive outside host cells and facilitate transmission between hosts.

Reticulate bodies (RBs) are the non-infectious, metabolically active form of Chlamydiae. They replicate and multiply within host cells, converting back to elementary bodies before being released to infect other cells or hosts.

Therefore, Chlamydiae occur in both elementary bodies and reticulate bodies during different phases of their life cycle.

Answer: Between positive and negative

Rickettsiae are small, obligate intracellular bacteria that are generally difficult to stain using the Gram staining technique. When stained using the Gram stain, rickettsiae often respond as “between positive and negative” or “poorly staining.”

Due to their unique cell wall structure and properties, rickettsiae do not neatly fit into the categories of Gram-positive or Gram-negative staining. They may appear variably stained or inconsistently stained when subjected to Gram staining, leading to difficulty in classification. Therefore, the response of rickettsiae to Gram staining is often not distinctly positive or negative.

The correct answer is Elementary bodies and Reticulate bodies. Chlamydiae can exist in two distinct forms: elementary bodies and reticulate bodies.

• Elementary bodies are the infectious form of the bacterium. They are small, dense forms that are resistant to environmental factors.
• Reticulate bodies are the replicating form of the bacterium. They are larger, less dense forms that are metabolically active.

Chlamydiae typically exist as reticulate bodies within host cells. However, when they are ready to spread to new cells, they differentiate into elementary bodies. Elementary bodies are released from the host cell and can then infect new cells. Once inside a new cell, elementary bodies differentiate back into reticulate bodies and begin to replicate.

Here is a table summarizing the two forms of Chlamydiae:

Answer: 1-5 %

The lipid content in the cell wall of Gram-positive bacteria typically ranges from 1 to 5%. Gram-positive bacterial cell walls contain lower amounts of lipids compared to Gram-negative bacteria, whose cell walls have a higher lipid content due to the presence of an outer lipid membrane.

Answer: Thick in Gram positive than Gram negative

The cell wall in Gram-positive bacteria is generally thicker than in Gram-negative bacteria. Gram-positive cell walls contain a thick layer of peptidoglycan, providing structural support, while Gram-negative bacteria have a thinner peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides (LPS).

So, to answer your question, the statement “Thick in Gram positive than Gram negative” is correct regarding the thickness of the cell wall.

Answer: Gram negative bacteria

Gram-negative bacteria typically have a higher lipid content compared to Gram-positive bacteria. This difference primarily arises from the presence of an outer membrane in Gram-negative bacteria, which contains lipopolysaccharides (LPS) and phospholipids, contributing to a higher lipid content in their cell walls. Gram-positive bacteria have a thick peptidoglycan layer but lack the outer membrane seen in Gram-negative bacteria, resulting in a lower lipid content overall.

Answer: Decolorises the cells

During the Gram staining process, alcohol (or a similar decolorizing agent) serves to decolorize the cells. This step removes the crystal violet-iodine complex from the Gram-negative bacteria, making them colorless. In contrast, Gram-positive bacteria retain the crystal violet-iodine complex due to their thicker peptidoglycan layer and resist decolorization.

Answer: Pink

Gram-negative bacteria typically appear pink after Gram staining. The pink coloration is due to the counterstain (safranin or fuchsine) used in the staining process. During Gram staining, Gram-negative bacteria lose the initial crystal violet-iodine complex and take up the counterstain, giving them their characteristic pink color.

Answer: Violet

Gram-positive bacteria typically appear violet or purple after Gram staining. The retention of the crystal violet-iodine complex by the thick peptidoglycan layer in Gram-positive bacteria results in their characteristic violet or purple coloration.

Answer: 90%

In Gram staining, typically, a solution of 90% ethanol or isopropanol is used for the decolorization step. The concentration of alcohol used is around 90%, ensuring effective removal of the crystal violet-iodine complex from Gram-negative bacteria while preserving the stain in Gram-positive bacteria.

Answer: Crystal violet, Iodine solution, Alcohol, Saffranine

The correct answer is Crystal violet, Iodine solution, Alcohol, Saffranine. The order of stains in Gram-staining procedure is as follows:

1. Crystal violet. This is the primary stain, and it stains all bacteria purple.
2. Iodine solution. This is the mordant, and it helps to fix the crystal violet dye in the cell walls of Gram-positive bacteria.
3. Alcohol. This is the decolorizing agent, and it removes the crystal violet dye from the cell walls of Gram-negative bacteria.
4. Safranin. This is the counterstain, and it stains Gram-negative bacteria red.

Answer: D. pneumoniae

The correct answer is D. pneumoniae. Streptococcus pneumoniae is a Gram-positive bacterium that does not produce pigment. Pseudomonas aeruginosa, Serratia marcescens, and Staphylococcus aureus are all Gram-negative bacteria that produce pigments.

• Pseudomonas aeruginosa produces pyocyanin, a blue-green pigment.
• Serratia marcescens produces prodigiosin, a red pigment.
• Staphylococcus aureus produces carotenoids, which are yellow-orange pigments.

Streptococcus pneumoniae does not produce any pigments, so it is the exception to the list.

Here is a table summarizing the pigment production of the four bacteria:

Answer: Malachite green

The correct answer is Malachite green. Endospores can be stained with Malachite green. Malachite green is a basic dye that is used to stain the cytoplasm and endospores of bacteria. During endospore staining, the bacteria are first heated to break down the cell walls of vegetative cells. This allows the malachite green dye to penetrate the endospores. The vegetative cells are then decolorized, leaving the endospores stained green.

• Safranine is a counterstain that is used to stain Gram-negative bacteria red in Gram staining.
• Crystal violet is a primary stain that is used to stain all bacteria purple in Gram staining.
• Methylene blue is a basic dye that is used to stain bacterial cells as well as nuclear material.

Answer: Simple binary fission

Bacteria typically multiply through a process called binary fission. In binary fission, a single bacterial cell divides into two identical daughter cells, each containing a copy of the genetic material. This process allows bacteria to rapidly increase their population under favorable conditions.

Spore formation is a method some bacteria use to survive unfavorable conditions, where a single bacterial cell forms a resistant spore. Conjugation involves the transfer of genetic material between two bacterial cells, while gametes are specialized reproductive cells involved in sexual reproduction, a process not typical for bacteria.

Bacteria can also reproduce through other methods, such as conjugation, transformation, and transduction. However, these methods are less common than binary fission.

• Conjugation is a process in which bacteria exchange genetic material by direct cell-to-cell contact.
• Transformation is a process in which bacteria take up DNA from the environment.
• Transduction is a process in which bacteria exchange genetic material by means of a virus.

These methods of reproduction allow bacteria to exchange genetic material, which can lead to the development of new traits. This can be important for bacteria, as it can help them to adapt to new environments or to resist antibiotics.

Answer: Methylene blue

Metachromatic granules in bacteria can be stained with Methylene blue. These granules show metachromasia, appearing in a color different from the stain used. Methylene blue is commonly employed to visualize these granules within bacterial cells.

Incorrect options:

1. Saffranine: Saffranine is a stain used in Gram staining and is not typically used to stain metachromatic granules.
2. Crystal violet: Crystal violet is another stain used in Gram staining, but it is not specific for staining metachromatic granules.
3. Pienic acie: This term seems to be a misspelling; it might refer to penicillin or picric acid, neither of which is used to stain metachromatic granules.

Answer: Polymetaphosphates

Metachromatic granules are chemically composed of Polymetaphosphates. These granules are storage structures found in certain bacteria, primarily consisting of polymers of phosphate ions. They exhibit metachromasia, where they appear in colors distinct from the stain used due to their phosphate composition.

Incorrect options:

1. Lipids: Metachromatic granules are not primarily composed of lipids. They are predominantly phosphate-based.
2. Proteins: While proteins are essential components of cells, metachromatic granules are not primarily composed of proteins; their main constituents are phosphate compounds.
3. Polysaccharide: Although bacterial cells contain various polysaccharides, metachromatic granules are not primarily composed of polysaccharides. They are mainly phosphate-based structures.

Answer: Rhodococcus agilis

Staphylococcus is a genus of Gram-positive cocci that are commonly found on the skin and mucous membranes of humans and other animals. Staphylococcus aureus is the most important species in this genus and is the cause of a variety of infections, including skin infections, pneumonia, and blood infections.
Meningococcus is a genus of Gram-negative cocci that are the causative agents of meningitis and other meningococcal diseases. Meningococcus is a common inhabitant of the human nasopharynx.
Gonococcus is a genus of Gram-negative cocci that are the causative agents of gonorrhea. Gonorrhea is a sexually transmitted infection that can cause inflammation of the urethra, cervix, and other reproductive organs.
Rhodococcus agilis is a genus of Gram-positive cocci that are found in the environment. Rhodococcus agilis is a motile coccus and is capable of degrading a variety of hydrocarbons.

Answer: Shigella flexneri

• Salmonella typhi bacteria are motile bacteria and they use their flagella to move around.
• Klebsiella pneumoniae bacteria are also motile bacteria, and it too uses flagella for movement.
• Bacillus anthracis bacteria are motile bacteria. They, too, have flagella to move around. However, Bacillus anthracis bacteria can also form spores, which are dormant forms of the bacteria that can resist harsh environmental conditions.
• Shigella flexneri bacteria are non-motile bacteria, this means that they do not have any flagella and therefore cannot move around on their own.

Therefore, Shigella flexneri bacteria are the correct answer to the question: Which of the following bacteria is non-motile?

Answer: Haemaggulation test

Fimbriae are demonstrated by the Haemagglutination test. It is a test that is used to detect the presence of fimbriae on bacteria. Fimbriae are hair-like appendages that are found on the surface of some bacteria. They can be used to attach to surfaces, such as host cells, and to move around.

In the haemagglutination test, bacteria are mixed with red blood cells. If the bacteria have fimbriae, they will be able to agglutinate (clump together) the red blood cells. This is because the fimbriae will bind to the receptors on the surface of the red blood cells.

The haemagglutination test is a quick and easy way to detect the presence of fimbriae. It is also a very specific test, as it will only agglutinate bacteria that have fimbriae.

Here are the steps of the haemagglutination test:

1. Mix the bacteria with red blood cells in a test tube.
2. Incubate the test tube for a few minutes.
3. Observe the test tube for agglutination.

Answer: Flagella

Bacterial locomotion is primarily accomplished by flagella. Flagella are whip-like appendages that extend from the surface of the bacterial cell and provide motility by rotating in a propeller-like motion, enabling the bacteria to move through liquid environments.

Fimbriae, on the other hand, are hair-like structures found on the surface of bacteria that aid in attachment to surfaces or host cells but are not primarily involved in bacterial locomotion.

The cytoskeleton in bacteria provides structural support and plays a role in cell division and maintaining cell shape but is not directly involved in bacterial locomotion.

Answer: Lysosomes

The organelles containing hydrolytic enzymes responsible for breaking down cellular waste and foreign materials are Lysosomes. These membrane-bound organelles are known as the “garbage disposals” of the cell, where enzymes within them perform the breakdown of various macromolecules.

Incorrect options:

1. Mitochondria: Mitochondria are the powerhouses of the cell, responsible for generating energy in the form of ATP through cellular respiration. They do not contain hydrolytic enzymes for cellular waste breakdown.
2. Golgi complex: The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids but does not primarily contain hydrolytic enzymes for degradation.
3. Ribosomes: Ribosomes are cellular structures responsible for protein synthesis and do not contain hydrolytic enzymes for waste breakdown.

Answer: All of these

The virulence determining antigens of microorganisms may be all of these. The following are the virulence determining antigens of microorganisms:

• Proteins and polysaccharides. These are the most common types of virulence factors. Proteins can be toxins, and polysaccharides can form a capsule around the cell that protects it from the immune system.
• Carbohydrate – protein complexes. These are also common virulence factors. They can be involved in adhesion to host cells, and they can also be toxins.
• Polysaccharide – Phospholipid – Protein complexes. These are the least common type of virulence factor, but they can be very effective. They are found in some of the most dangerous bacteria, such as E. coli and Neisseria meningitidis.
• Lipopolysaccharides (LPS) – In many Gram-negative bacteria, endotoxins or lipopolysaccharides (LPS) are the primary virulence factor.

Answer: Serum

Capsule formation in bacteria typically occurs in the presence of Serum. Serum contains various nutrients and factors that promote the growth and encapsulation of certain bacterial species, aiding in the formation of capsules around the bacterial cell wall. Capsules serve protective functions and contribute to the virulence of certain bacteria.

Answer: Cell Wall

The differences between Gram-positive and Gram-negative bacteria primarily reside in the cell wall. Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, while Gram-negative bacteria have a thinner layer of peptidoglycan but possess an outer membrane containing lipopolysaccharides (LPS) and porins, which Gram-positive bacteria lack.

Incorrect options:

1. Nucleus: The differences between Gram-positive and Gram-negative bacteria are not related to the presence or structure of the nucleus. Bacteria, in general, lack a true nucleus.
2. Cell membrane: While both Gram-positive and Gram-negative bacteria have cell membranes, the key difference lies in the cell wall structure rather than the cell membrane composition.
3. Mesosomes: Mesosomes are not directly responsible for the differences between Gram-positive and Gram-negative bacteria. They are internal structures within bacterial cells believed to be artifacts of sample preparation rather than distinct organelles.

Answer: Phycology

The study of algae is known as Phycology. Phycology encompasses the scientific study of algae, including their classification, morphology, physiology, ecology, and distribution in various environments.

Incorrect options:

1. Algalogy: While this term might seem appropriate, the commonly accepted term for the study of algae is phycology.
2. Mycology: Mycology is the study of fungi, including their biology, taxonomy, and ecology.
3. Bacteriology: Bacteriology focuses on the study of bacteria, including their structure, genetics, ecology, and medical relevance.

Answer: Phytoplankins

The free-floating algae are known as Phytoplankton. These are microscopic algae that live in aquatic environments, drifting or floating near the water’s surface. They form the base of the aquatic food chain and play a crucial role in aquatic ecosystems by producing a significant portion of Earth’s oxygen through photosynthesis.

Incorrect options:

1. Benthons: Benthos refers to organisms living at the bottom of a body of water, attached to or in close association with the substrate, but it doesn’t specifically refer to free-floating algae.
2. Seaweeds: Seaweeds are larger, macroscopic algae attached to substrates in marine environments rather than being free-floating.

Answer: All the above

Sexual reproduction in algae can be carried out by different mechanisms, including Isogamy, Anisogamy, and Oogamy.

Isogamy involves the fusion of similar gametes that are morphologically alike in size and structure. Anisogamy is the fusion of two gametes that differ in size and often in structure. Oogamy involves the fusion of a larger, non-motile egg cell with a smaller, motile sperm cell.

Answer: 10°C – 35°C

Most molds are capable of growing in a temperature range between 10°C to 35°C. This range provides favorable conditions for their growth and proliferation, although some molds may have specific temperature preferences within this range.

Answer: Saphrophytes

Molds that obtain nutrition from dead and decaying matter are called Saprophytes or saprotrophs. They decompose and feed on organic material, breaking it down into simpler compounds, playing a crucial role in the recycling of nutrients in ecosystems.

• Parasites feed off living organisms.
• Commensals live in association with other organisms without causing harm or benefit to the host.

Answer: Brown algae

Alginic acids and their salts are primarily obtained from the walls of Brown algae. Brown algae, such as kelp and seaweeds, contain alginates (salts of alginic acid) in their cell walls. These compounds have various industrial applications, including in food, pharmaceuticals, and manufacturing processes due to their gelling, thickening, and stabilizing properties.

While red algae also contain polysaccharides, they typically contain carrageenans and agars rather than alginates. Green algae, on the other hand, are not typically known for producing significant amounts of alginates.

Answer: Oogamy

Among the options listed, the advanced type of sexual reproduction in algae is Oogamy. Oogamy is a more specialized form of sexual reproduction where a larger, non-motile egg cell (female gamete) is fertilized by a smaller, motile sperm cell (male gamete).

Isogamy involves the fusion of similar gametes, while anisogamy is the fusion of gametes that are different in size and often in structure. Oogamy, with its specialized and distinct gametes, is considered a more advanced form of sexual reproduction observed in many algae species.

Answer: Tadpole shape

A tadpole-shaped bacteriophage has a head and a tail. The head contains the bacteriophage’s genetic material, and the tail is used to attach the bacteriophage to the host cell and inject its genetic material into the cell.

Other shapes of bacteriophages include:

• Brick-shaped: These bacteriophages have a rectangular or cuboidal head
• Bullet-shaped: These bacteriophages have a long, thin head that resembles a bullet
• Helical: These bacteriophages have a helical head that resembles a spring.
  The shape of a bacteriophage is determined by the proteins that make up its capsid. The capsid is the protein shell that surrounds the bacteriophage’s
• genetic material. The proteins in the capsid assemble themselves into a specific shape, which is determined by their amino acid sequence.

The shape of a bacteriophage can also affect its ability to infect host cells. For example, tadpole-shaped bacteriophages are able to infect a wider range of host cells than other shapes of bacteriophages.

Answer: Virion

A virion is the complete, infectious form of a virus. It consists of a nucleic acid genome (DNA or RNA) enclosed in a protein capsid. The capsid protects the genome from damage and the environment. Some viruses also have an envelope, which is a lipid bilayer that surrounds the capsid.

Virions are produced inside host cells during the viral replication cycle. Once the virions are produced, they are released from the host cell and can infect other cells.

The other options are not correct:

• Capsid is the protein shell that surrounds the viral genome.
• Nucleocapsid is a complex of the viral genome and capsid.

Answer: Pox virus

Among the options provided, the Pox virus is relatively large compared to other viruses. Poxviruses are some of the largest and most complex viruses known, containing a large DNA genome and a complex structure. However, it’s essential to note that viruses vary widely in size, and while poxviruses are relatively large, there might be other viruses classified as large or giant viruses depending on different criteria used for measurement.

Answer: Protozoans

The structure known as a Pellicle is primarily found in Protozoans. It is a flexible yet supportive layer found in certain protozoans, serving as a protective covering for the cell membrane. This structure allows the organism to maintain its shape while being flexible enough for movement.

It’s important to note that while algae, fungi, and bacteria have various structures serving different purposes, the pellicle specifically refers to a feature found in some protozoans.

Answer: All of the above

All of the listed options, which include Streptomyces, Spirillospora, Frankia, and Dermatophillia, are examples of actinomycetes. Here’s a brief overview of each:

1. Streptomyces: This is the most well-known genus of actinomycetes, producing over two-thirds of all known antibiotics. They are commonly found in soil and play a crucial role in the decomposition of organic matter.
2. Spirillospora: These actinomycetes are characterized by their helical shape and are often found in aquatic environments. They play a role in nitrogen fixation, converting atmospheric nitrogen into a form that can be used by plants.
3. Frankia: These specialized actinomycetes form symbiotic relationships with leguminous plants, such as beans and peas, helping them fix nitrogen from the air. They are essential for the growth and survival of these plants.
4. Dermatophillia: These actinomycetes can cause skin infections in animals, including cattle, sheep, and horses. They are commonly found in soil and can be transmitted through direct contact.

These examples highlight the diverse range of actinomycetes and their significant roles in various ecosystems. They contribute to soil health, play a role in the nitrogen cycle, and are an important source of antibiotics.

Answer: All of these

All of the mentioned options, which include nitrates, nitrites, and ammonium salts, are inorganic forms of nitrogen accepted by bacteria.

Bacteria play a crucial role in the nitrogen cycle, a process that converts nitrogen from one form to another. These inorganic forms of nitrogen are essential for bacterial growth and development, as they serve as sources of nitrogen for various metabolic processes.

Nitrates (NO3-): Bacteria can utilize nitrates as a source of nitrogen for protein synthesis and other cellular processes. The process of nitrate reduction or denitrification converts nitrates into nitrogen gas, returning nitrogen to the atmosphere.

Nitrites (NO2-): Nitrites can also be used by bacteria as a source of nitrogen. The process of nitrite reduction or denitrification converts nitrites into nitrogen gas or ammonia.

Ammonium salts (NH4+): Ammonium salts are another form of inorganic nitrogen that bacteria can readily utilize. The process of ammonium assimilation converts ammonium ions into organic nitrogen compounds that can be used for various cellular purposes.

The ability of bacteria to utilize these inorganic forms of nitrogen is essential for their survival and for the overall nitrogen cycle. Without bacteria, nitrogen would be unavailable for many organisms, disrupting ecosystems and the overall balance of the nitrogen cycle.

Overall, nitrates, nitrites, and ammonium salts are all important inorganic forms of nitrogen that are accepted by bacteria, playing a vital role in their metabolism and in the nitrogen cycle.

Answer: Negative staining

Negative staining is a technique in which a heavy metal stain is applied to the background around the specimen, rather than to the specimen itself. This leaves the specimen unstained and makes it appear bright against the dark background.

Negative staining is a very effective way to improve the contrast of specimens for electron microscopy. It is often used to visualize the morphology of bacteria, viruses, and other microorganisms.

The other options are not correct:

• Positive staining involves applying a stain to the specimen itself. This can also improve contrast, but it is not as effective as negative staining.
• Shadow staining is a technique in which a metal shadow is cast on the specimen. This can also improve contrast, but it is not as common as negative staining.

Answer: Differential staining

When more than one stain is used in a staining procedure, it is referred to as Differential staining. This staining technique involves the use of multiple stains to distinguish between different parts of the specimen or different types of microorganisms, highlighting their different structures or properties. Gram staining and acid-fast staining are examples of differential staining techniques used to differentiate between bacterial groups based on their cell wall properties.

The other options are not correct:

• Simple staining uses only one stain.
• Negative staining uses only one stain, and the stain is applied to the background around the specimen, not to the specimen itself.

Answer: Negative staining

When the background surrounding the sample (specimen) is stained rather than the sample itself, it is referred to as Negative staining. This technique involves staining the area around the specimen, leaving the specimen unstained or lightly stained, which enhances contrast and visibility of the specimen against the dark background.

The other options are not correct:

• Simple staining involves applying a single stain to the specimen, not to the background.
• Differential staining involves applying multiple stains to the specimen, not to the background.

Answer: Simple staining

Simple staining is the simplest and most common type of staining. It involves applying a single stain to the specimen. The stain can be either basic or acidic. Basic stains bind to negatively charged structures in the cell, such as nucleic acids, while acidic stains bind to positively charged structures in the cell, such as proteins.

Simple staining is used to visualize the overall morphology of a specimen and to identify the presence of certain cellular structures. For example, simple staining can be used to identify the presence of bacteria in a smear of sputum or to identify the presence of chromosomes in a cell.

The other options are not correct:

• Negative staining involves applying a stain to the background around the specimen, rather than to the specimen itself. This leaves the specimen unstained and makes it appear bright against the dark background.
• Differential staining involves applying multiple stains to the specimen, each of which binds to a different type of cellular structure. This allows different cellular structures to be distinguished from each other. For example, Gram staining is a differential staining technique that can be used to distinguish between Gram-positive and Gram-negative bacteria.

Answer: Heterotrophes

The group of bacteria that depend on organic sources in nature for their energy requirements are termed Heterotrophs. These organisms obtain energy by breaking down organic compounds produced by other organisms and use these compounds as a source of carbon and energy for their metabolic processes.

The other options are not correct:

• Chemotrophs are organisms that obtain energy from the oxidation of inorganic or organic matter.
• Phototrophs are organisms that obtain energy from sunlight.
• Organotrophs are organisms that use organic carbon as their source of carbon.

Answer: Hydrogen – Oxydising bacteria

Bacillus Schlegelii is known as a Hydrogen-Oxidizing Bacteria. These bacteria use hydrogen as an energy source for their metabolism, oxidizing it to obtain energy.

Other options are incorrect:

• Sulfur-Oxidising Bacteria: These bacteria use sulfur compounds as a source of energy.
• Iron-Oxidising Bacteria: These bacteria use iron compounds as a source of energy.
• Nitrite-Oxidizing Bacteria: These bacteria convert nitrite to nitrate.

Answer: Thiobacillus

Sulfur-oxidizing bacteria are a group of bacteria that can use sulfur compounds as a source of energy. They play an important role in the sulfur cycle, the process by which sulfur is converted from one form to another in the environment.

Thiobacillus bacteria are found in a wide range of habitats, including soil, water, and hydrothermal vents. They are also used in commercial applications, such as biomining and wastewater treatment.

The other options are not correct:

• Alcaligenes is a genus of bacteria that are known for their ability to degrade organic matter.
• Pseudomonas is a genus of bacteria that are known for their ability to produce a variety of pigments and toxins.

Answer: Nitrobacter

Nitrobacter is a genus of aerobic, chemolithotrophic bacteria that play an important role in the nitrogen cycle. Nitrobacter bacteria oxidize nitrite to nitrate, which is a form of nitrogen that can be used by plants.

The other options are not correct:

• Nitrosomonas bacteria convert ammonia to nitrite.
• Nitrosococcus bacteria are similar to Nitrosomonas bacteria, but they are found in different environments.
• Azatobacter bacteria are able to fix atmospheric nitrogen, converting it to ammonia.
• Nitrobacter bacteria are found in soil and water, and they play an important role in agricultural productivity. Nitrobacter bacteria also help to remove nitrite from wastewater, which can be harmful to humans and animals.

Answer: Extreme thermophiles

Archaea are a domain of single-celled organisms that are characterized by their unique molecular characteristics and their ability to live in extreme environments. Archaea are found in a wide range of habitats, including hot springs, hydrothermal vents, salt lakes, and acidic soils.

Some archaea are able to survive in temperatures as high as 113 °C (235 °F), making them the most heat-tolerant organisms known. These archaea are known as extreme thermophiles.

Other archaea are able to survive in high-salt environments, high-acid environments, or high-pressure environments. These archaea are known as halophiles, acidophiles, and barophiles, respectively.

Archaea play an important role in the global ecosystem. They are involved in nutrient cycling, methane production, and other important processes.

Answer: Saprophytes

The majority of bacteria are considered Saprophytes. These organisms decompose organic matter, breaking down dead and decaying material into simpler compounds, thus playing a vital role in recycling nutrients in ecosystems.

While many bacteria are saprophytic, there are also bacteria that exist as symbionts, commensals, or parasites in various environments and ecosystems.

The other options are not correct:

• Symbionts are organisms that live in a close relationship with another organism, such as the bacteria that live in the intestines of humans.
• Commensals are organisms that live in close association with another organism without harming it or benefiting from it.
• Parasites are organisms that live in or on another organism and feed off of it, causing harm to the host.

Answer: All of these

All of the mentioned options – bacteria in symbiotic association, the group of fungi in symbiotic association, and the groups participating in symbiotic association – can be considered symbionts.

Symbionts are organisms that live in close association with one another. This symbiotic relationship can be beneficial, harmful, or neutral.

• Bacteria in symbiotic association: Bacteria are a diverse group of microorganisms that can form symbiotic relationships with other organisms, including plants, animals, and fungi. These symbiotic relationships can range from mutualism, where both organisms benefit, to commensalism, where one organism benefits without harming the other, to parasitism, where one organism benefits at the expense of the other.
• The group of fungi in symbiotic association: Fungi are another diverse group of microorganisms that can form symbiotic relationships with other organisms, including plants and animals. These symbiotic relationships can also range from mutualism to commensalism to parasitism.
• The groups participating in symbiotic association: Symbiotic relationships can involve any two or more organisms, from bacteria and fungi to plants and animals. The type of relationship that develops depends on the specific organisms involved and the environment in which they live.

Answer: Both Lipolytic and Proteolytic

The enzymes responsible for decomposition are primarily Both Lipolytic and Proteolytic. Lipolytic enzymes break down lipids, while proteolytic enzymes break down proteins. Both types of enzymes play crucial roles in the decomposition process by breaking down complex organic molecules into simpler compounds that can be utilized by decomposers or recycled in ecosystems.

Answer: Plasmids

Self-replicating, small circular DNA molecules present in bacterial cells are known as plasmids. Plasmids are extrachromosomal DNA molecules that are not essential for the survival of the bacteria, but they can provide them with certain advantages, such as antibiotic resistance or the ability to metabolize certain compounds. Plasmids are often used in genetic engineering to transfer genes between different organisms.

The other options are incorrect:

• Cosmids are artificial plasmids that are used to clone large fragments of DNA. They are made by combining a plasmid with a cos site, which is a DNA sequence that allows the plasmid to be packaged into bacteriophages.
• Plasmomers are not a real term.
• Plastids are organelles found in plant cells that are responsible for photosynthesis. They contain their own DNA, but they are not plasmids.