Which is not one the three general mechanisms of adaptations of extremophiles?

• Adaptation

• Exclusion

• Detoxification

• Reconstruction

Which of the following is not an adaptation of microorganisms in low temperature environment?

• branched chain fatty acids

• short chain fatty acids

• trans-unsaturated fatty acids

• polar carotenoids

Answer explanation

Which of the following is not true about the adaptations of microorganisms in extreme pH?

• Cell walls of alkaliphiles have cell wall that contains acidic polymers

• One adaptation of acidophiles is that the cell membrane is highly impermeable to protons

• Membrane channels of acidophiles have reduced pore size

• Alkaliphiles have a slightly higher internal pH

• Proton uncoupling by organic acids is one of the adaptations by alkaliphiles

Answer explanation

Some adaptations under acidic conditions:

-Proton pump and other ion-flux mechanisms

-pH-dependent membrane-bound transporters, enzymes and respiratory components

-Membrane impermeability to protons

Image from: Baker-Austin, C., and Dopson, M. (2007). Life in acid: pH homeostasis in acidophiles. Trends Microbiol. 15, 165–171. doi: 10.1016/j.tim.2007.02.005

Which of the following is not true about the adaptations of extremophiles in high saline environments?

• High amount of aromatic amino acid residues

• Involves accumulation of molar concentrations of potassium through the K+ symport mechanism

• Cytoplasmic proteins must be adapted to an ionic cytoplasm

• High amounts of acidic amino acids over basic residues

What is an environment with a neutral to slight alkaline pH and a dominance of sodium (about 20%) and chloride ions?

• Solfatara

• Thalassohaline

• Coal Refuse Pile

• Athalassohaline

Which of the following is true about biofilms?

• Typically composed of a single species of microorganism

• Encased microcolonies of bacterial cells detached from a surface of polysaccharides

• Unlike the planktonic lifestyle, biofilms cannot offer protection for bacteria against environmental, chemical, and mechanical stresses.

• Aggregation of microorganisms marked by the excretion of a protective and adhesive matrix

What is the proper sequence of biofilm formation?

• Adhesion of pioneer bacteria, surface conditioning, slime formation, secondary colonizers, fully functioning biofilm

• Adhesion of pioneer bacteria, surface conditioning, slime formation, secondary colonizers, fully functioning biofilm

• Surface conditioning, adhesion of pioneer bacteria, slime formation, secondary colonizers, fully functioning biofilm

• Surface conditioning, slime formation, adhesion of pioneer bacteria, secondary colonizers, fully functioning biofilm

Answer explanation

Image from: https://www.researchgate.net/publication/277833092_Antibacterial_Strategies_for_Titanium_Biomaterials/figures

Which of the following is not true about how biofilms are spread?

• Detachment is any mechanism which causes individual cells or cell masses to separate from the substratum to which the biofilm is attached

• Rapidly growing biofilms exhibit slower rate of detachment that fast growing ones.

• Seeding dispersal is a phenomenon which begins as the interior of a biofilm micro-colonies liquefies and ends as the outer layer of the colony is breached permitting the escape of plantonic cells

• In rippling, the mass of biofilm appears to move in waves propelled at as much as 1 mm/hour by the force of the flowing water

• Detachment is usually associated with dispersal and dispersal is typically a concomitant event with detachment

Answer explanation

Detachment may include passive forces such as abrasion due to the impact of particles suspended in the fluid flowing past. Dispersal is facilitated by any mechanism in which “propagules” (fragments or single cells) are caused to leave the existing biofilm with the potential of initiating a new biofilm elsewhere. In rolling, a roughly spherical mass of cells can be seen to roll down stream in the direction of the bulk fluid flow. Image from: https://www.cs.montana.edu/webworks/projects/stevesbook2/contents/chapters/chapter002/section002/blue/page003.html

Which of the following is not true regarding how bacteria find and attach to surfaces and how biofilms are formed?

• Bacteria form biofilms for food.

• Bacteria form biofilms for protection since these serve as protective shields.

• After adaptation to biofilm mode of life, microorganisms are found to be more hydrophilic as compared to planktonic or wild-type isolates and cell surface hydrophilicity increased with incubation time

• Diffusion limitations imparted by the biofilm structure result in local variations in nutrient availability, pH, and oxygen tension.

Answer explanation

In one study, the individual characteristics of the bacterial isolates were studied in mono-species biofilm consortia. After adaptation to biofilm mode of life, all of these isolates were found to be more hydrophobic as compared to planktonic or wild-type isolates and cell surface hydrophobicity increased with incubation time. Source: Mirani, Z. A., Fatima, A., Urooj, S., Aziz, M., Khan, M. N., & Abbas, T. (2018). Relationship of cell surface hydrophobicity with biofilm formation and growth rate: A study on Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. Iranian journal of basic medical sciences, 21(7), 760–769. https://doi.org/10.22038/IJBMS.2018.28525.6917

Which of the following factors affecting attachment and growth of biofilms are considered under substratum effects?

• Conditioning films

• Hydrodynamic effects

• Ionic strength

• Flow velocity

• Microbial interactions

Answer explanation

The formation of a biofilm is known to be strongly dependent on substrate properties including hydrophobicity/hydrophilicity, structure, and roughness. The adsorption of (macro)molecules on the substrate, also known as conditioning film, changes the physicochemical properties of the surface and affects the bacterial adhesion. Conditioning film formed by culture medium affects the roughness, hydrophobicity, and chemical composition of the surface. Source: Lorite, G. S., Rodrigues, C. M., de Souza, A. A., Kranz, C., Mizaikoff, B., & Cotta, M. A. (2011). The role of conditioning film formation and surface chemical changes on Xylella fastidiosa adhesion and biofilm evolution. Journal of colloid and interface science, 359(1), 289–295. https://doi.org/10.1016/j.jcis.2011.03.066