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Microbiology - Soil Microbiology

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    Study Guide Microbiology – Soil Microbiology 1. Other Biogeochemical Cycles Soil is not only important for the nitrogen cycle — it is also the main setting for several other biogeochemical cycles . These cycles move essential elements through living organisms, the soil, water, and the atmosphere. Some of the most important ones involve phosphorus, sulfur, carbon, and oxygen . 1.1 The Phosphorus Cycle Phosphorus is essential for life. Living organisms use phosphorus to make: • Nucleotides (the building blocks of DNA and RNA) • Phospholipids (key parts of cell membranes) • Phosphorylated proteins Phosphorus enters soil and water mainly as phosphate ions . These come from sources such as: • Decaying plants and crops • Leaf litter • Garbage and organic waste Role of Microorganisms In the soil, microorganisms interact with phosphorus compounds like: • Calcium phosphate • Magnesium phosphate • Iron phosphate Microbes break phosphorus free from these compounds and absorb it as the phosphate ion (PO ₄ ³ ⁻ ) . This phosphate is then used to build DNA, RNA, phospholipids, and other vital molecules. When microorganisms are eaten by larger organisms, phosphorus moves up the food chain , becoming more concentrated at higher levels.

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    Study Guide 1.2 The Sulfur Cycle Sulfur makes up only about 1 percent of a cell’s dry weight , but it is still very important. It is needed to form: • Amino acids such as cystine and methionine • The antioxidant glutathione • Many enzymes Sulfur in the Soil Several types of bacteria play key roles in the sulfur cycle. • Sulfate - reducing bacteria live in muddy, oxygen - poor environments like swamps. They break down sulfur - containing amino acids and produce hydrogen sulfide (H ₂ S) . • Hydrogen sulfide has a strong rotten - egg smell and often accumulates in swamp mud. Recycling Sulfur In the next steps of the cycle: • Photosynthetic sulfur bacteria use hydrogen sulfide in anaerobic conditions and convert it into elemental sulfur (S) . • Colorless sulfur bacteria (such as Thiobacillus , Beggiatoa , and Thiothrix ) further oxidize sulfur compounds into sulfate ions . Plants absorb sulfate ions and use them to make sulfur - containing amino acids, completing the cycle. 1.3 The Carbon Cycle Most organic matter in soil comes from dead plant material , including: • Fallen leaves • Rotting trees • Decaying roots Animal remains also add carbon to the soil after death.

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    Study Guide Role of Microorganisms Bacteria and fungi are essential in the carbon cycle. They: • Break down proteins, fats, and carbohydrates • Recycle carbon so it can be reused by living organisms Without this recycling, carbon would remain locked in complex molecules, and life would eventually decline. How Carbon Is Recycled • Microbes release extracellular enzymes that digest organic matter into soluble products. • These products are then metabolized into: o Carbon dioxide o Small organic acids (such as acetic and propionic acids) • Plants absorb these simpler compounds through their roots. Material that is not fully broken down becomes humus , a stable and nutrient - rich part of soil. 1.4 The Oxygen Cycle Oxygen is essential for cellular respiration , including: • Glycolysis • The Krebs cycle • Electron transport and chemiosmosis The atmosphere is the main reservoir of oxygen used in these processes. Oxygen Production Oxygen is continuously returned to the atmosphere by: • Green plants • Photosynthetic microorganisms , such as cyanobacteria During photosynthesis , these organisms split water molecules and release oxygen as a by - product. Oxygen Use

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