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Methods in Microbiology (GATE)

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Which of the following organisms use organic compounds as a source for carbon, electrons and energy?

  1. Hydrogen bacteria

  2. Fungi

  3. Cyanobacteria

  4. Purple and green non-sulphur bacteria


Correct Option: B
Explanation:

Fungi are chemoorganoheterotrophs and use organic compounds as a source of carbon, electrons and energy.

Rhodobacter belongs to which of the following nutritional groups?

  1. Photoorganoautotroph

  2. Photoorganoheterotroph

  3. Photolithoheterotroph

  4. Photolithoautotroph


Correct Option: B
Explanation:

Rhodobacter is a photosynthetic bacterium. It uses photon energy for making food, organic oxidising donor source and organic carbon source. Thus, it is a photoorganoheterotroph.

Which of the following minerals provides heat resistance to bacterial endospores?

  1. Iron

  2. Calcium

  3. Magnesium

  4. Phosphorus


Correct Option: B
Explanation:

Calcium is a component of endospores and provides heat resistance to them.

Which of the following functions of bacteria may suffer due to a deficiency of potassium?

  1. Endospore formation

  2. Cell respiration

  3. RNA synthesis

  4. Protein synthesis


Correct Option: D
Explanation:

Potassium is required for the activity of enzymes involved in protein synthesis. Thus, protein synthesis in bacteria would suffer due to the deficiency of potassium.

What is the minimum requirement of classifying a source as an organic nutrient provider?

  1. It should provide at least C and O.

  2. It should provide at least H and O.

  3. It should provide at least C and H.

  4. It should at least provide C, H and O.


Correct Option: C
Explanation:

An organic nutrient provider should at least provide C and H.

Which of the following staining techniques is used to stain the volutin or metachromatic granules of C. diphtheria, so that the granules are clearly visible in light microscope?

  1. Auramine-Rhodamine technique

  2. Calcofluor White staining

  3. Albert staining

  4. Fontana's staining


Correct Option: C
Explanation:

Albert staining is used to stain the volutin or metachromatic granules of C. diphtheria. On Albert staining, the metachromatic granules appear blue in color.

Which of the following nutritional modes is followed by Oceanithermus profundus?

  1. Chemoorganoheterotropy

  2. Chemoorganoautotropy

  3. Chemolithoheterotropy

  4. Chemolithoautotropy


Correct Option: C
Explanation:

Oceanithermus profundus follows chemolithoheterotrophic mode of nutrition. It is a moderately thermophilic, organotrophic, microaerophilic and facultatively chemolithotrophic bacterium isolated from a deep-sea hydrothermal vent site at 13-N in the East Pacific Rise.

Which of the following vitamins is essential for bio-synthetic reactions that require CO2 fixation?

  1. Nicotinic acid

  2. Pantothenic acid

  3. Biotin

  4. Pyridoxine


Correct Option: C
Explanation:

Biotin is essential for bio-synthetic reactions that require CO2 fixation.

During which of the following steps of sample processing in electron microscopy are the samples treated with propylene oxide?

  1. Cryofixation

  2. Chemofixation

  3. Embedding

  4. Shadowing


Correct Option: C
Explanation:

Samples are passed through propylene oxide in the process of embedding. After treating with propylene oxide, samples are infiltrated with an epoxy resin and then embedded directly in water-miscible acrylic resin.

Which of the following sentences is correct about differential interference contrast microscopy (DIC)?

  1. No bright diffraction halo is obtained around the image.

  2. Misleading 3D appearance of image is obtained.

  3. Phase-shift image is created.

  4. It was invented by Robert Hoffman.


Correct Option: A
Explanation:

This is true. In DIC, image is similar to that obtained by phase contrast microscopy but without the bright diffraction halo.

Mixotrophs are unicellular organisms which can switch between different metabolic modes. Which of the following organisms exhibit(s) mixotrophy?

  1. Purple non-sulphur bacteria

  2. Purple sulphur bacteria

  3. Cyanobacteria

  4. Chroococcales


Correct Option: D
Explanation:

Chroococcales is a mixotroph. It can switch between different metabolic modes like photoautotrophy, photoheterotrophy and chemoheterotrophy.

Which of the following organisms get their carbon for biosynthesis from carbon dioxide?

  1. Aerobic, glucose-respiring bacteria

  2. Ammonia-oxidising bacteria

  3. Anaerobic, glucose-respiring bacteria

  4. Glucose-fermenting bacteria


Correct Option: B
Explanation:

Ammonia-oxidising bacteria are chemolithotrophic bacteria that get carbon for biosynthesis from carbon dioxide.

Oxygen radicals produced by microorganisms in the process of photosynthesis are finally converted to water by the action of superoxide dismutase, catalase or peroxidase. Which of the following organisms possesses peroxidase but lacks catalase?

  1. Micrococcus luteus

  2. Enterococcus faecalis

  3. Fusobacterium

  4. Methanococcus


Correct Option: B
Explanation:

Enterococcus faecalis is an aerotolerant organism as it only contains peroxidase.

Which of the following is/are photoheterotroph(s)?

  1. Thermoacidophiles

  2. Green non-sulphur bacteria

  3. Kelp algae

  4. Nitrobacter


Correct Option: B
Explanation:

Green non-sulphur bacteria are photoheterotrophs. They use light for energy and use organic compounds to satisfy their carbon needs.

In the given paragraph, composition of a bacteriological medium is given. Which type of culture medium is it for the growth of Thiobacillus thiooxidans?

Component            Amount            Function

NH4Cl                     0.52 g              N source

KH2PO4                  0.28 g             P and K source

MgSO4 7H2O          0.25 g             S and Mg2+ source

CaCl2 2H2O            0.07 g             Ca++ source

Elemental Sulphur  1.56 g            Energy source

CO2                          5%                 C source  

Water                     1000 ml

pH 3.0

  1. Minimal medium

  2. Defined enrichment medium

  3. Complex medium

  4. Selective enrichment medium


Correct Option: B
Explanation:

The above mentioned medium would act as a defined enrichment medium for the growth of Thiobacillus thiooxidans. It is chemically defined and it contains elemental sulphur as carbon source, enriching it for the growth of Thiobacillus thiooxidans.

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