GATE Overflow for GATE ESE - Recent activity in Environmental Microbiology

Edited: GATE ES 2026 | Question: 44

Wed, 15 Apr 2026 11:19:32 +0000

A thermal process, at a specific temperature, results in $2-\log _{10}$ removal of non-thermotolerant pathogenic microorganisms from a water sample in $20$ min.

The time needed to achieve $99.999\%$ removal of these microorganisms under similar condition is $\_\_\_\_$ $\min$ (answer in integer).

Edited: GATE ES 2026 | Question: 43

Wed, 15 Apr 2026 11:15:45 +0000

In a batch culture experiment, $2$ cells of a microorganism were added to a growth medium. During the experiment, a lag phase of $1$ hour was first experienced by the added cells, in which no cell multiplication occurred. Afterwards, cells started multiplying exponentially with a doubling time of $1$ hour.

After total $8$ hours of experiment, the number of cells present in the growth medium was $\_\_\_\_$ (answer in integer).

Edited: GATE ES 2026 | Question: 33

Wed, 15 Apr 2026 10:48:02 +0000

Which of the following statements is/are CORRECT based on the electron donor $\text{(ED)}$ and electron acceptor $\text{(EA)}$ used in various bacterial mediated reactions in wastewater treatment?

In anaerobic heterotrophic acid fermentation, organic compounds are used as both $\text{ED}$ and $\text{EA}$.
In anaerobic heterotrophic methanogenesis, volatile fatty acids and $\mathrm{CO}_{2}$ are used as $\text{ED}$ and $\text{EA}$, respectively.
In denitrification process by denitrifiers, organic compounds and $\mathrm{CO}_{2}$ are used as $\text{ED}$ and $\text{EA}$, respectively.
In aerobic autotrophic iron oxidation, $\text{Fe} \text{(II)}$ and $\mathrm{O}_{2}$ are used as $\text{ED}$ and $\text{EA}$, respectively.

Edited: GATE ES 2026 | Question: 28

Wed, 15 Apr 2026 10:25:50 +0000

Which ONE of the following options is CORRECT with respect to sequential breakdown of deoxyribonucleic acid (DNA) into lower-molecular weight compounds?

Deoxyribonucleic acid → $2$-deoxyribose → Nucleosides → Nucleotides
Deoxyribonucleic acid → $2$-deoxyribose → Nucleotides → Nucleosides
Deoxyribonucleic acid → Nucleotides → Nucleosides → $2$-deoxyribose
Deoxyribonucleic acid → Nucleosides → Nucleotides → $2$-deoxyribose

Edited: GATE ES 2026 | Question: 8

Wed, 15 Apr 2026 07:49:12 +0000

Malaria is caused by pathogenic $\_\_\_\_\_\_\_$.

bacteria
fungi
protozoa
viruses

Edited: GATE ES 2026 | Question: 7

Wed, 15 Apr 2026 07:48:49 +0000

The major class of enzymes catalyzing the cleavage of $C-C, C-O, C-N$, or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds in any biochemical reactions is $\_\_\_\_$.

lyases
transferases
oxidoreductases
hydrolases

Edited: GATE ES 2025 | Question: 34

Mon, 02 Jun 2025 19:46:02 +0000

If microbial growth occurs under substrate unlimited conditions, according to Monod's kinetics, choose the correct option(s) from the following

Microbial growth follows zero order with respect to substrate concentration.
Microbial growth follows first order with respect to substrate concentration.
Specific growth rate is half of maximum specific growth rate.
Specific growth rate is almost equal to maximum specific growth rate.

Edited: GATE ES 2025 | Question: 28

Mon, 02 Jun 2025 19:41:18 +0000

Consider the following statements on microbial metabolism

Utilization of carbon for cell synthesis is termed as anabolism.
During catabolism, adenosine triphosphate (ATP) is converted into adenosine diphosphate (ADP).

Choose the correct option from the following

(i) and (ii) are correct
(i) and (ii) are incorrect
(i) is correct and (ii) is incorrect
(i) is incorrect and (ii) is correct

Edited: GATE ES 2025 | Question: 20

Mon, 02 Jun 2025 16:55:38 +0000

Choose the correct option(s) from the following regarding the symbiotic relationships

Lichens are a symbiotic association of fungi and bacteria. They can survive in extreme conditions of air pollution.
Lichens are a symbiotic association of fungi and bacteria. The fungi can absorb water and minerals from atmosphere, and bacteria can generate foods.
Lichens are a symbiotic association of fungi and algae. They can survive in extreme conditions, but are very sensitive to air pollution.
Lichens are a symbiotic association of fungi and algae. The fungi can absorb water and minerals from atmosphere, and algae can generate food through photosynthesis.

Edited: GATE ES 2025 | Question: 15

Mon, 02 Jun 2025 16:51:58 +0000

Choose the correct statement(s) from the following regarding the structure/ reproduction of microorganisms

Prokaryotes do not have nucleus but Eukaryotes have nucleus.
Both Prokaryotes and Eukaryotes have nucleus.
No binary fission happens in Eukaryotes, however, Prokaryotes rely on binary fission for reproduction.
Both Prokaryotes and Eukaryotes rely on binary fission for reproduction.

Edited: GATE ES 2025 | Question: 5

Mon, 02 Jun 2025 15:55:48 +0000

Which one of the following is performed by autotrophic bacteria?

Aerobic biodegradation of organic matter
Anaerobic biodegradation of organic matter
Aerobic nitrification
Anaerobic de-nitrification

Recategorized: GATE ES 2024 | Question: 5

Mon, 21 Apr 2025 17:04:33 +0000

Tuberculosis is predominantly caused by __________.

Entamoeba histolytic
Salmonella typhi
Mycobacterium bovis
Bacillus cereus

Recategorized: GATE ES 2024 | Question: 4

Mon, 21 Apr 2025 17:04:31 +0000

Rod shaped bacterial cells are called ________.

Bacilli
Cocci
Spirilla
Diplococci

Recategorized: GATE ES 2024 | Question: 35

Mon, 21 Apr 2025 17:03:25 +0000

Which of the following statement$\text{(s)}$ is/are CORRECT?

DNA is composed of nucleotides
Five types of nitrogenous bases occur in DNA
Each phosphate is attached to two deoxyribose units in a single strand of DNA
The ratio of adenine to guanine is always $1: 1$ in a double stranded DNA.

Recategorized: GATE ES 2024 | Question: 34

Mon, 21 Apr 2025 17:03:22 +0000

With reference to disinfection, which of the following statement(s) is/are CORRECT?

Ethanol damages lipid structures in the bacterial cell membrane
Mercuric chloride inactivates cellular enzymes containing sulfhydryl groups
Glutaraldehyde inactivates protein
Isopropyl alcohol cannot be used as a disinfectant.

Recategorized: GATE ES 2024 | Question: 33

Mon, 21 Apr 2025 17:03:19 +0000

Enzymes with the class of enzymes are listed in the table.

Enzyme	Class of Enzyme
$\text{(a)}$ Lactate dehydrogenase	$\text{(i)}$ Isomerases
$\text{(b)}$ Alanine racemase	$\text{(ii)}$ Transferases
$\text{(c)}$ Lipase	$\text{(iii)}$ Oxidoreductases
$\text{(d)}$ Hexokinase	$\text{(iv)}$ Hydrolases

Select the correct match(es)

$\text{(a) - (iii); (b) - (i)}$
$\text{(c) - (iv); (d) - (ii)}$
$\text{(a) - (ii); (b) - (iv)}$
$\text{(c) - (iii); (d) - (i)}$

Recategorized: GATE ES 2023 | Question: 5

Mon, 21 Apr 2025 17:01:22 +0000

Read the following statements

I. Photosynthesis takes place within the chloroplasts of the eukaryotes, whereas the breakdown of complex molecules to yield energy takes place in the cytoplasm and in the mitochondria.

II. Photosynthesis takes place within the chloroplasts of the prokaryotes, whereas the breakdown of complex molecules to yield energy takes place in the cytoplasm and in the mitochondria.

III. All living organisms retain the enzymatic machinery to partially oxidise glucose without the help of oxygen. This breakdown of glucose to pyruvic acid is called glycolysis.

IV. All living organisms retain the enzymatic machinery to completely oxidise glycerol without the help of oxygen. This breakdown of glycerol to citric acid is called glycolysis.

The correct choice is

$\text{I}$ and $\text{III}$ are correct
$\text{II}$ and $\text{IV}$ are correct
$\text{I}$ is correct whereas $\text{III}$ is incorrect
$\text{II}$ is correct whereas $\text{IV}$ is incorrect

Recategorized: GATE ES 2023 | Question: 6

Mon, 21 Apr 2025 17:01:19 +0000

Read the following statements

i. Aerobic heterotrophic bacteria uses organic matter for carbon source and energy source.
ii. Aerobic heterotrophic bacteria uses carbon dioxide for carbon source and energy source.
iii. Aerobic autotrophic bacteria uses carbon dioxide for carbon source and reduced substances for energy source.
iv. Aerobic autotrophic bacteria uses organic matter for getting energy.

The correct choice is

(i) is correct; (iii) is correct
(iv) is correct; (i) is incorrect
(i) is correct; (iv) is correct
(ii) is correct; (iv) is incorrect

Recategorized: GATE ES 2023 | Question: 7

Mon, 21 Apr 2025 17:01:16 +0000

A student wants to decide electron acceptor for aerobic, facultative and anaerobic bacteria. In this context, read the following statements

i. Dissolved Oxygen (DO) can act as electron acceptor for aerobic bacteria

ii. Nitrite can act as electron acceptor for aerobic bacteria.

iii. Dissolved Oxygen (DO) can act as electron acceptor for anaerobic bacteria.

iv. Nitrite can act as electron acceptor for facultative bacteria.

The correct choice is

(i) is correct; (iv) is correct
(ii) is correct; (iii) is incorrect
(ii) is correct; (iii) is correct
(i) is correct; (ii) is correct

Recategorized: GATE ES 2023 | Question: 22

Mon, 21 Apr 2025 17:00:34 +0000

The ratio of the moles of $\mathrm{CO}_2$ evolved to the moles of $\mathrm{O}_2$ consumed in respiration also called the respiratory quotient, is calculated for a carbohydrate $\left(\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6\right)$ as substrate and found to be $1$. Under similar conditions, for a fatty acid $\left(\mathrm{C}_{51} \mathrm{H}_{98} \mathrm{O}_6\right)$ as substrate, the respiratory quotient is ____________ (rounded off to two decimal place).

Recategorized: GATE ES 2023 | Question: 27

Mon, 21 Apr 2025 17:00:20 +0000

Which one of the following statements is NOT correct?

Photophosphorylation is the synthesis of $\text{ATP}$ from $\text{ADP}$ and inorganic phosphate in the presence of light.
The process through which $\text{ATP}$ is synthesized by cells $\text{(in mitochondria and chloroplasts)}$ is called phosphorylation.
The Calvin cycle $\text{(carboxylation, reduction, and regeneration)}$ occurs in all photosynthetic plants ($\text{C3, C4 or any other)}$.
$\text{C3}$ plants have a special type of leaf anatomy, they tolerate higher temperatures, they show a response to high light intensities, have high rate of photosynthesis and reduced rate of photorespiration as compared to $\text{C4}$ plants.

Recategorized: GATE ES 2023 | Question: 28

Mon, 21 Apr 2025 17:00:17 +0000

Read the following statements

I. Bacteriophage is an anaerobic bacterium.

II. Male-specific bacteriophage infect via the pili of other microorganisms including viruses.

III. Bacteriophage is found in human as well as in animal excreta.

IV. Bacteriophage can not indicate the presence of bacteria.

The correct choice is

$\text{(I), (III)}$ and $\text{(IV)}$ are correct
$\text{(IV)}$ is correct; $\text{(III)}$ is incorrect
Both $\text{(III)}$ and $\text{(IV)}$ are incorrect
Both $\text{(III)}$ and $\text{(IV)}$ are correct

Recategorized: GATE ES 2023 | Question: 29

Mon, 21 Apr 2025 17:00:14 +0000

Read the following statements

i. In endogenous metabolism by aerobic bacteria, electron acceptor is present inside the cells.
ii. In endogenous metabolism by aerobic bacteria, electron acceptor is dissolved oxygen.
iii. The endogenous metabolism is linked to fermentative metabolism.
iv. In exogenous metabolism by aerobic bacteria, enzyme mediated electron transfer happens within the cells.

The correct choice is

$\text{(i)}$ is correct; $\text{(iii)}$ is correct
$\text{(ii)}$ is correct; $\text{(iii )}$ is incorrect
$\text{(iii)}$ is incorrect; $\text{(iv)}$ is incorrect
$\text{(iii)}$ is correct; $\text{(iv)}$ is correct

Recategorized: GATE ES 2022 | Question: 7

Mon, 21 Apr 2025 16:47:40 +0000

Reverse Transcriptase Polymerase Chain Reaction is an analytical procedure used in detection of pathogenic microorganisms. Which one of the following statements is NOT correct in this context?

It is used for identifying presence or absence of specific RNA in samples.
It is used only for identifying Corona Viruses, including SARS CoV2 in samples.
It cannot differentiate between viable and inactivated viruses.
It is based on conversion of RNA to DNA followed by DNA amplification.

Recategorized: GATE ES 2022 | Question: 28

Mon, 21 Apr 2025 16:46:43 +0000

For an exponentially growing microbial culture, the specific growth rate $(\mu)$ is related to its doubling time $\left(\mathrm{t}_{\mathrm{d}}\right)$ by which one of the following relations?

$\quad t_{d}=\mu$
$\mathrm{t}_{\mathrm{d}}=\mu^{2}$
$\mathrm{t}_{\mathrm{d}}=\frac{1}{\mu} \ln 2$
$\quad t_{d}=\frac{1}{2} \ln \mu$

Recategorized: GATE ES 2022 | Question: 29

Mon, 21 Apr 2025 16:46:35 +0000

A microbial culture, with a specific growth rate of $\mu_{1}$ (per hour), is being grown in a continuous reactor at steady state with hydraulic retention time (HRT) of $24$ hours. This reactor is subjected to a perturbation by reducing the HRT to $12$ hours. The reactor recovers from the perturbation and comes to a new steady state with a new specific growth rate of $\mu_{2}$ (per hour). Which one of the following statements is correct?

$\quad \mu_{1}=\mu_{2}$
$\quad \mu_{1}=0.5 \mu_{2}$
$\mu_{2}=0.5 \mu_{1}$
$\quad \mu_{2}=e^{0.5} \mu_{1}$

Recategorized: GATE ES 2022 | Question: 34

Mon, 21 Apr 2025 16:46:24 +0000

A typical plasmid-free bacterial cell having a single chromosome consists of $\sim 55 \%$ protein, $\sim 3 \%$ DNA and $\sim 21 \%$ RNA, where " $\% "$ " represents percentage of dry weight. Assuming there are 2500 different types of protein molecules (with at least one copy number) being expressed in a living bacterial cell at any given time, which of the following statement(s) is/are NOT correct with respect to the number of intracellular DNA, RNA and protein molecules?

$\mathrm{DNA}=\mathrm{RNA}=$ Protein $\geq 2500$
$\quad \mathrm{DNA}=\mathrm{RNA}=1 ;$ Protein $\geq 2500$
DNA $=1 ;$ RNA $=$ Protein $\geq 2500$
$\mathrm{DNA}=1 ; \mathrm{RNA}>$ Protein $\geq 2500$

Recategorized: GATE ES 2021 | Question: 8

Mon, 21 Apr 2025 15:42:24 +0000

Which of the following is the terminal electron acceptor in the electron transport chain of aerobic respiration?

Water
$\mathrm{NADH}$
$\mathrm{O}_{2}$
Cytochrome-c

Recategorized: GATE ES 2021 | Question: 18

Mon, 21 Apr 2025 15:42:02 +0000

Which of the following pairing of nucleotide bases is present in double helix DNA?

Thymine - Cytosine
Adenine - Thymine
Cytosine - Adenin
Uracil - Thymine

Recategorized: GATE ES 2021 | Question: 24

Mon, 21 Apr 2025 15:41:44 +0000

In a sample, the growth of microbial cells started with an initial concentration of $5 \times 10^4$ cells per millilitre $(\mathrm{mL})$ of the sample. After a certain time period, the cell concentration was found to be $1280 \times 10^4$ cells per $\mathrm{mL}$ of the sample. Assuming binary fission of cells and no cell death, the number of generations of cell growth occurred in this time period is $\text{(answer in integer)}$.

Recategorized: GATE ES 2021 | Question: 35

Mon, 21 Apr 2025 15:41:12 +0000

Which of the following is true for the nitrifying bacteria belonging to genus Nitrobacter?

They are autotrophs.
They are eukaryotes.
They convert chemical energy to cellular energy using mitochondria.
They convert $\mathrm{NO}_{3}^{-}$to $\mathrm{NO}_{2}^{-}$.

Recategorized: GATE ES 2021 | Question: 38

Mon, 21 Apr 2025 15:41:04 +0000

Which of the following is/are correct for the process of glycolysis?

There is net decrease in standard Gibbs free energy.
The end product is glyceraldehyde 3-phosphate.
Fist pluase incluces the plosphorylation of the glucose molecule.
It results in the net gain of $\mathrm{NADH}$.