Microbial activities and their applications - MicroCore RC

This principle/process states that living organisms interact with their inorganic surroundings on Earth to form a synergistic and self-regulating, complex system that helps to maintain and perpetuate the conditions for life on the planet.

• Biodegradation

• Biogeochemical cycling

• Bioremediation

• Gaia hypothesis

Which of the following elements is cycled most intensely?

• Fe

• Mg

• Ca

• Cr

• S

Which of the folowing is a nitrite oxidizer?

• Nitrosomonas

• Nocardia

• Azospirillum

• Nitrobacter

• Pseudomonas

Answer explanation

Nitrobacter winogradskyi is a chemolithotrophic bacterium that plays a role in the nitrogen cycle by oxidizing nitrite to nitrate. Image from: https://genome.jgi.doe.gov/portal/nitwi/nitwi.home.html

Which of the following is true about oxidative sulfur transformations and sulfur oxidizers?

• Conversion of sulfite, thiosulfate, or elemental sulfur to hydrogen sulfide

• Conversion of inorganic sulfur compounds by sulfur oxidizers such as Desulfuromonas

• Gain energy for cell synthesis and growth by coupling the oxidation of organic compounds or molecular hydrogen (H2) to the reduction of sulfate (SO4 2−) to sulfide (H2S, HS−)

• Elemental sulfur converted to sulfuric acid

Which of the following is not an iron oxidizer?

• Acidithiobacillus ferroxidans

• Sphaerotilus natans

• Gallionella ferruginea

• Geobacter metallireducens

Answer explanation

Geobacter metallireducens is an obligate anaerobic iron reducer that can grow with Fe3+ as the sole electron acceptor. Image from: Childers, S., Ciufo, S. & Lovley, D. Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis. Nature 416, 767–769 (2002). https://doi.org/10.1038/416767a

Which principle states that no natural organic compound is resistant to biodegradation provided that environmental conditions are favorable?

• Microbial Biodegradation

• Microbial Infallibility

• Microbial Bioconversion

• Microbial Xenobiosis

Answer explanation

The ‘principle of microbial infallibility’ was a mainstay of microbial physiology and environmental microbiology in earlier decades. This principle asserts that wherever there is an energetic gain to be made from environmental resources, microorganisms will find a way to take advantage of the situation.

What makes xenobiotic substances resistant to biodegradation?

• Excessively low molecular size

• Unusual bonds or bond sequences

• Unusual substitutions

• Lack of suitable permeases

• Excessive toxicity of parent compounds

Which of the following processes can result to the biodegradation of xenobiotic compounds?

• Oxidative methylation

• Natural restoration

• Anaerobic dechlorination

• Reductive dechlorination