1NGS_MEcology_Distribution of Microorganisms in Natural Systems

Refers to the community of organisms that inhabit the surface layer of water bodies, particularly at the air-water interface.

• Pleuston

• Benthos

• Neuston

• Neritic zone

• Littoral zone

Answer explanation

The term neuston refers to the group of organisms associated with the surface layer of lakes, oceans, and slow-moving sections of streams. This assemblage includes species living just beneath the water surface (hyponeuston), those above but still immersed in the water (epineuston), and organisms that move across the surface on hydrophobic structures (superneuston), which is more accurately considered a form of epineuston.

Reference:

Thorp, J. H. (2014). Functional relationships of freshwater invertebrates. In Elsevier eBooks (pp. 65–82). https://doi.org/10.1016/b978-0-12-385026-3.00004-8

Toleukhanov, A. (2012). Bio-reactive two-phase transport and population dynamics in underground storage of hydrogen: natural self-organisation. Proceedings. https://doi.org/10.3997/2214-4609.20143214

This can be determined by considering the ratio of the number of microorganisms in the rhizosphere soil to the number of corresponding microorganisms in the soil remote from the roots.

• Rhizosphere index

• Rhizosphere effect

• Rhizobacterial diversity

• Rhizosphere ratio

• None of the choices

Answer explanation

In the rhizosphere, plant roots directly impact the composition and density of the soil's microbial community, a phenomenon known as the rhizosphere effect. This effect can be measured by the ratio of microorganisms in the rhizosphere soil (R) to those in soil away from the roots (S), referred to as the R/S ratio.

Typically, the R/S ratio ranges from 5 to 20, though it is not uncommon for the ratio to reach 100, meaning microbial populations in the rhizosphere can be up to 100 times greater than in root-free soil. The extent of the rhizosphere effect varies depending on the specific plant and its physiological stage.

References:

Cai, A., Tang, S., Waqas, M. A., Wang, B., Tian, D., Zhang, Y., Li, Y., Ashraf, M. N., & Ren, T. (2022). Magnitude, direction, and drivers of rhizosphere effect on soil nitrogen and phosphorus in global agroecosystem. International Soil and Water Conservation Research, 11(3), 482–493. https://doi.org/10.1016/j.iswcr.2022.07.004

Zaborowska, M., Kucharski, J., & Wyszkowska, J. (2017). Brown Algae and Basalt Meal in Maintaining the Activity of Arylsulfatase of Soil Polluted with Cadmium. Water Air & Soil Pollution, 228(8). https://doi.org/10.1007/s11270-017-3449-7

https://plantlet.org/rhizosphere-its-effects/

What is the primary function of microbial biofilms in aquatic environments?

• Enhance water clarity

• Protect microorganisms from predation

• Promote sedimentation

• Facilitate nutrient cycling

• None of the above

Answer explanation

The formation of biofilms is viewed as a survival strategy for microbiota. In particular, the aggregation of microorganisms within the extracellular polymeric substance (EPS) matrix offers protection against predation, osmotic stress, and ultraviolet light.

References:
Cooney, C., Sommer, B., Marzinelli, E. M., & Figueira, W. F. (2023). The role of microbial biofilms in range shifts of marine habitat-forming organisms. Trends in Microbiology, 32(2), 190–199. https://doi.org/10.1016/j.tim.2023.07.015

De Carvalho, C. C. C. R. (2018). Marine Biofilms: A successful Microbial Strategy with Economic Implications. Frontiers in Marine Science, 5. https://doi.org/10.3389/fmars.2018.00126

The following are adaptation of microorganisms in environments with high temperature except:

• Decreased number of double bonds in membrane fatty acids

• Increased fatty acid chain length

• Decreased amounts of hopanoids and cholesterol in their membranes

• Change in amino acid sequences of proteins

• None of the choices

Which of the following statements is incorrect regarding halophilic organisms that employ a high salt strategy to thrive in hypersaline environments?

• They have a narrow range of tolerance to salinity.

• All their cytoplasmic proteins are adapted to an ionic cytoplasm.

• Their proteins have high amounts of acidic amino acids over basic residues.

• Their proteins have high amounts of aromatic amino acid residues.

• None of the choices