Atmo-Ecosphere and Plant as Microbial Habitat - MicroCore RC

Generally, when the altitude increases, what happens to the atmospheric pressure, temperature, and concentration of available oxygen?

• decrease, increase, decrease

• decrease, decrease, decrease

• increase, increase, increase

• increase, decrease, increase

• decrease, decrease, increase

Answer explanation

With increasing height in the atmosphere, the atmospheric pressure declines and the concentration of the available oxygen decrease to a point that precludes aerobic respiration. Image from: https://kids.britannica.com/students/assembly/view/107829

Which of the following is not a way by which bioaerosols may form?

• Splash from falling raindrops

• Rapidly moving water currents

• Forced air streams in sewage treatment plants

• Spray from breaking waves

• None of the aformentioned

Answer explanation

Microbes can become airborne by the eruption of rising bubbles through the sea-surface microlayer. If the wind speed is high enough, spume drops can be ejected from the breaking wave crest. The bubble-bursting results in an enrichment of microbes in the aerosol compared to subsurface water.

Image from: References

Fröhlich-Nowoisky, J., Kampf, C. J., Weber, B., Huffman, J. A., Pöhlker, C., Andreae, M. O., … Pöschl, U. (2016). Bioaerosols in the Earth system: Climate, health, and ecosystem interactions. Atmospheric Research, 182, 346–376. doi:10.1016/j.atmosres.2016.07.018

Which of the following is not a reason why spores are better adapted in the atmosphere?

• Metabolically active

• Relatively of small size and low density

• Produced in very high numbers

• With protective structures

Answer explanation

Bacterial spores are the most dormant form of bacteria since they exhibit minimal metabolism and respiration, as well as reduced enzyme production. Endospores are resistant to the chemical agents, e.g., triphenylmethane dyes, and can even protect the bacterial cells against ultraviolet radiation, extreme pH gradients, drought, and nutrition depletion. Image from: https://biologyease.com/endospore/

Which of the following is not a passive mechanism that discharge spores into the atmosphere?

• Shedding under gravity

• Ballistospore discharge

• Rain splash

• Shedding in convection currents

• Mechanical disturbance

Answer explanation

The gleba is a solid mass of spores, generated within an enclosed area within the sporocarp. When a critical pressure is reached inside the cells of the elastic membrane, the membrane everts rapidly, discharging the gleba from the cup.

Which of the following is not a property of the environment that affects the dispersion of air spore in air currents?

• Turbulence

• Wind movement

• Air viscocity

• Degree of surface roughness

• Pattern of atmospheric circulation

 

Which of the following can be observed by looking at the ratio of the number of microorganisms in the rhizosphere soil (R) to the number of corresponding microorganisms in soil remote from the roots (S) (R/S ratio)?

• Allee's principle

• Phytomicrobiome

• Phyllosphere microflora

• Rhizosphere effect

Answer explanation

Rhizosphere effect is measured on quantitative basis using the R:S ratio number of microorganisms in the rhizosphere (R) is increased relative to the number in the bulk soil (S). Image from: https://www.researchgate.net/publication/308915540_The_Role_of_Root_Taper_on_Soil_Erodibility_A_Critique_on_the_Tripartite_Classification_of_Rooted_Soils

Which of the following factors does not affect the microbial community structure of the rhizosphere?

• Plant phenotype

• Exposure to disease-suppresive soil

• Plant species

• Root exudate composition

• Plant developmental stage

Which of the following organisms does not belong to the most common bacteria on leaves?

• Xanthomonas

• Pseudomonas

• Erwinia

• Bacillus

Which of the following statements is true about the positive effects of soil microorganisms on plants?

• Infected plants perceive pathogen invasion in roots or shoot and subsequently increase the secretion of microbe-stimulatory compounds in infected roots.

• Plant microbiome assists in the weathering of minerals and but not the degradation of recalcitrant organic matter

• Leghemoglobin buffers the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules

• Root exudates and other rhizodeposits stimulate and/or inhibit various microbes

Answer explanation

Leghemoglobin has a high affinity for oxygen (Km ~ 0.01 µM), about ten times higher than the β chain of human hemoglobin. This allows an oxygen concentration that is low enough to allow nitrogenase to function, but high enough that it can provide the bacteria with oxygen for respiration. Image from: Madigan, M. T., Martinko, J. M., Bender, K. S., Buckley, D. H., Sattley, W.M. & Stahl, D. A. (2018). Brock biology of microorganisms (Fifteenth edition.). Boston: Pearson.

Which of the following statements on the effect of plant growth-promoting bacteria and plants is not true?

• Siderophores sequester iron which is used by the plant to produce chlorophyll. Iron-deficient plants have yellow leaves

• Diazotrophs fix atmospheric nitrogen to form ammonia, nitrates, and sulfates, which are utilized by the plants

• IAA is a plant growth-hormone which can be produced by PGPB and is important in regulating growth and developmental processes such as cell division and elongation

• Phosphate-solubilizing bacteria play a critical role in soil by mineralizing organic P, solubilizing inorganic P minerals, and storing large amounts of P in biomass

Answer explanation

Diazotrophs are bacteria and archaea that fix gaseous nitrogen in the atmosphere into a more usable form such as ammonia. Image from: https://www.researchgate.net/publication/310843288_PHYSIOLOGY_OF_NITROGEN_FIXATION_IN_LEGUMES_UNDER_ELEVATED_CO2/figures?lo=1