Question

Try to answer each question in about 50 words.

1. What is the limitation on what bacteria can utilize as nutrients?

2. A farm soil is heavily limed for two consecutive years to bring the pH from 5.2 to 6.5. What changes do you expect in the bacteria community?

3. How is soluble Fe2+ restored into the soil solution at pH 5?

4. A microcolony of bacteria has a plasmid it acquired from the environment. This plasmid confers a new enzyme function to this microcolony. These bacteria can utilize the field pesticide as a nutrient and decompose it. No other bacteria in this field can utilize this pesticide molecule. Describe what might happen to the plasmid over several years, in that field.

5. A Pseudomonad growing on cellulose in the soil organic matter, from cellulose digestion, runs out of cellulose to transport into the cytoplasm. What might happen in the bacteria as it responds to this change?

6. Under which conditions might you smell H2S from soil?

7. Under what abiotic conditions might phosphorous become insoluble and inaccessible to cells?

8. Based on your knowledge of soils, which parameters increase aggregate size?

9. Would bacteria that secrete organic acids be useful to fine roots in the absorption of Fe or P?

10. A pasture grazed regularly by cows for years has accumulated enviable amounts of C (as soil organic matter) and available phosphorous. The pasture grasses show signs of nitrogen deficiency. Why might that be? What might be happening to the bacteria?

11. What are example solutes that can be accumulated in the cytoplasm to increase its concentration, for osmoregulation?

12. Why is the soil called a giant biofilm?

Answer 1

Answer 1:)

The limitations of nutrients for bacteria depend upon the mode of food synthesis. Generally, bacteria are non-phototrophic and hence they utilize nitrogenous, sulfur compounds, and carbohydrates. The phototrophic bacteria such as blue green algae utilize CO₂ and H₂O for synthesis of glucose.

Answer 2:)

The range of pH that changed from 5.2 to 6.5 is getting less acidic therefore, during this change, more bacteria will evolve for lesser acidic and hence their cell wall can be thicker due to more peptidoglycan.

Answer 3 :)

At low pH like 5 provides breaking of Fe³⁺ into Fe²⁺ ions that are soluble in soil. Ferric ions are not soluble in soil. Some plants release protons in soil to reduce ferric ions into ferrous ions.

Answer 4:)

The bacteria might get the plasmid from those bacteria that became resistant to the pesticide. It happens due to mutations. Bacterial plasmids are prone to have mutations. First maximum population of a bacteria die due to the pesticide but some who lived make their population and become resistant to that pesticide.

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