12 Physical & Environmental Requirements for Growth - MicroCore

Which of the following elements are required by microorganisms?

• Carbon

• Nitrogen

• Sulfur

• Potassium

• All of the aforementioned elements are required

Answer explanation

Answer: E. Chemical nutrients such as carbon, nitrogen, sulfur and potassium are required for the growth of microbial populations. Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Yeung, A. T. (2010). Remediation technologies for contaminated sites. In Springer eBooks (pp. 328–369). https://doi.org/10.1007/978-3-642-04460-1_25

Generally, what is the temperature requirement of human pathogenic bacteria?

• Thermophiles

• Mesophiles

• Psychrophiles

• Psychrotrophic

• Halophiles

Answer explanation

Answer: B. Since normal human body temperature is 37°C, the majority of human pathogens are mesophiles, as are most of the organisms comprising the human microbiome.

 

Reference:

Gutierrez, C., Somoskovi, A., Natarajan, K., & Bell, D. (2018). Need for better adherence to optimal incubation temperature for quality laboratory diagnostics and antibiotic resistance monitoring. African Journal of Laboratory Medicine, 7(2). https://doi.org/10.4102/ajlm.v7i2.789

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Which of the following terms best describes microorganisms that can spoil refrigerated foods?

• Psychrotrophic

• Mesophilic

• Anaerobic

• Halophiles

• Acidophile

Answer explanation

Answer: A. Psychrotrophic bacteria are those that can grow at refrigeration temperatures and lead to the spoilage of product.

 

Reference:

Ahangari, H., Yazdani, P., Ebrahimi, V., Soofiyani, S. R., Azargun, R., Tarhriz, V., & Eyvazi, S. (2021). An Updated review on production of food derived bioactive peptides; focus on the psychrotrophic bacterial proteases. Biocatalysis and Agricultural Biotechnology, 35, 102051. https://doi.org/10.1016/j.bcab.2021.102051

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Yalew, K., Pang, X., Huang, S., Zhang, S., Yang, X., Xie, N., Wang, Y., Lv, J., & Li, X. (2024). Recent development in detection and control of psychrotrophic bacteria in dairy production: ensuring milk quality. Foods, 13(18), 2908. https://doi.org/10.3390/foods13182908

What part of the cell becomes fluid when subjected to high temperature?

• Nucleoid

• Cytoplasm

• Cell membrane

• Cell wall

Answer explanation

Answer: C. Membrane fluidity refers to the property of cell and organelle membranes that allows them to maintain their structural integrity and function. It is influenced by temperature, with higher temperatures leading to increased fluidity. Changes in membrane fluidity can affect membrane permeability, enzyme function, and the leakage of molecules and ions across the membrane.

 

Reference:

Los, D. A., & Murata, N. (2004). Membrane fluidity and its roles in the perception of environmental signals. Biochimica Et Biophysica Acta (BBA) - Biomembranes, 1666(1–2), 142–157. https://doi.org/10.1016/j.bbamem.2004.08.002

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Toxic forms of oxygen are detrimental to which group of bacteria?

• Obligate aerobe

• Microaerophile

• Facultative anaerobe

• Obligate anaerobe

Answer explanation

Answer: D. Obligate anaerobes are microorganisms that can only survive in oxygen-free environments, as free oxygen molecules are toxic to them. These include Clostridium tetani, Clostridium botulinum, and methanogens and lack a respiratory enzyme system. Thus, they can only facilitate anaerobic respiration.

 

Reference:

Lu, Z., Imlay, J.A. When anaerobes encounter oxygen: mechanisms of oxygen toxicity, tolerance and defence. Nat Rev Microbiol 19, 774–785 (2021). https://doi.org/10.1038/s41579-021-00583-y

Yan Liu,... Haiteng Deng, in Molecular Medical Microbiology (Third Edition), 2023. https://doi.org/10.1016/C2018-1-03862-7

Which of the following statements is true about pH as one of the factors affecting the growth and survival of microorganisms?

• The optimum pH of an individual pertains to its preferred external and internal pH

• No matter what extracellular pH a microorganisms prefers, the intracellular pH should be maintained near neutrality

• An acidophile can grow at pH 5.8

• One critical factor governing acidophily is the stability of the cytoplasmic membrane

Answer explanation

Answer: No matter what extracellular pH a microorganisms prefers, the intracellular pH should be maintained near neutrality

Microorganisms must keep their intracellular pH near neutral because most enzymes and structural proteins only remain stable and active in this range. For example, acidophiles adapt by maintaining pH homeostasis through proton pumps, impermeable membranes, and buffering systems, allowing survival in acidic environments while protecting enzyme function.

References:

Lund PA, De Biase D, Liran O, Scheler O, Mira NP, Cetecioglu Z, Fernández EN, Bover-Cid S, Hall R, Sauer M, O'Byrne C. Understanding How Microorganisms Respond to Acid pH Is Central to Their Control and Successful Exploitation. Front Microbiol. 2020 Sep 24;11:556140. doi: 10.3389/fmicb.2020.556140. PMID: 33117305; PMCID: PMC7553086.

https://microbeonline.com/ph-requirements-microorganism/

Pseudomonas aeruginosa is a common pathogen that infects the airways and lungs of patients with cystic fibrosis disease. Given its preferred site of infection, the bacterium is probably a/an:

• Obligate aerobe

• Aerotolerant anaerobe

• Obligate anaerobe

• Facultative anaerobe

Answer explanation

Answer: A. Pseudomonas aeruginosa are gram-negative, motile, nonfermenting, obligate aerobic rods that have minimal growth requirements in culture. Identification is usually based on the colony morphology, which is round with a fluorescent greenish color. Mucoid strains are prevalent in cystic fibrosis patients.

 

Reference: Carol F. Farver, Chapter 10 - Bacterial Diseases, Editor(s): Dani S. Zander, Carol F. Farver, In The Foundations in Diagnostic Pathology Series, Pulmonary Pathology, Churchill Livingstone, 2008, Pages 167-203, ISBN 9780443067419, https://doi.org/10.1016/B978-0-443-06741-9.50016-1. (https://www.sciencedirect.com/science/article/pii/B9780443067419500161)

Jurado-Martín, I., Sainz-Mejías, M., & McClean, S. (2021). Pseudomonas aeruginosa: An Audacious Pathogen with an Adaptable Arsenal of Virulence Factors. International Journal of Molecular Sciences, 22(6), 3128. https://doi.org/10.3390/ijms22063128

Maďar, M., Kačírová, J., Maďari, A., Mucha, R., Styková, E., & Nemcová, R. (2021). Cultivable bacterial diversity of the canine dental plaque as a potential source of bacterial infections. Acta Veterinaria Brno, 90(2), 171–178. https://doi.org/10.2754/avb202190020171

Which type of microorganisms can grow over wide ranges of water activity?

• Halophile

• Alkaliphile

• Neutrophile

• Osmotolerant

Answer explanation

Answer: D. Osmotolerant bacteria, such as Staphylococcus aureus can grow in a wide variety of environments with varying osmotic pressures. In fact this bacteria can be cultured in media containing sodium chloride (NaCl) concentrations as high as 3 M.

 

Reference: Rachel Watson. The Virtual Edge: Lab 6 Cultivation of Bacteria II. http://www.uwyo.edu/virtual_edge/ 

Stratford, M., Steels, H., Novodvorska, M., Archer, D. B., & Avery, S. V. (2019). Extreme osmotolerance and halotolerance in Food-Relevant yeasts and the role of Glycerol-Dependent cell individuality. Frontiers in Microbiology, 9. https://doi.org/10.3389/fmicb.2018.03238

Which of the following is NOT true about obligate aerobes?

• Require oxygen for growth

• Lacks superoxide dismutase and catalase

• Uses oxygen as final electron acceptor in aerobic respiration

• All of the choices are true about obligate aerobes

Answer explanation

Answer: Lack superoxide dismutase and catalase

Obligate anaerobes are unable to survive in oxygen because they lack the key enzymes—superoxide dismutase, catalase, and peroxidase—needed to detoxify reactive oxygen species. Without these defenses, toxic byproducts accumulate and damage cellular components, making oxygen lethal to them.

References:

Hentges DJ. Anaerobes: General Characteristics. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 17. Available from: https://www.ncbi.nlm.nih.gov/books/NBK7638/

https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(OpenStax)/09%3A_Microbial_Growth/9.02%3A_Oxygen_Requirements_for_Microbial_Growth

What do you call microorganisms that live in dry environments?

• Xerophiles

• Halotolerant

• Neutrophiles

• Osmotolerant

• Nikaphiles

Answer explanation

Answer: Xerophiles

The organisms, which have the ability to grow in extremely dry conditions or in the presence of very low water activity (below Aw 0.8), are considered to be xerophiles.

Reference:

Gupta, M. K. (2023). Isolation of microorganisms. In Elsevier eBooks (pp. 3–21). https://doi.org/10.1016/b978-0-12-816109-8.00001-5

Kanekar, P.P., Kanekar, S.P. (2022). Xerophilic and Xerotolerant Microorganisms. In: Diversity and Biotechnology of Extremophilic Microorganisms from India. Microorganisms for Sustainability. Springer, Singapore. https://doi.org/10.1007/978-981-19-1573-4_10

Marzban G, Tesei D. The Extremophiles: Adaptation Mechanisms and Biotechnological Applications. Biology. 2025; 14(4):412. https://doi.org/10.3390/biology14040412