Microbiology - Soil Microbiology | Anatomy and Physiology

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Study GuideMicrobiology–Soil Microbiology1.Other Biogeochemical CyclesSoil is not only important for thenitrogen cycle—it is also the main setting for several otherbiogeochemical cycles. These cycles move essential elements through living organisms, the soil,water, and the atmosphere. Some of the most important ones involvephosphorus, sulfur, carbon,and oxygen.1.1The Phosphorus CyclePhosphorus 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 proteinsPhosphorus enters soil and water mainly asphosphate ions. These come from sources such as:•Decaying plants and crops•Leaf litter•Garbage and organic wasteRole of MicroorganismsIn the soil, microorganisms interact with phosphorus compounds like:•Calcium phosphate•Magnesium phosphate•Iron phosphateMicrobes break phosphorus free from these compounds and absorb it as thephosphate ion (PO₄³⁻).This phosphate is then used to build DNA, RNA, phospholipids, and other vital molecules.When microorganisms are eaten by larger organisms, phosphorus moves up thefood chain,becoming more concentrated at higher levels.

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Study Guide1.2The Sulfur CycleSulfur makes up only about1 percent of a cell’s dry weight, but it is still very important. It is neededto form:•Amino acids such ascystineandmethionine•The antioxidantglutathione•Many enzymesSulfur in the SoilSeveral types of bacteria play key roles in the sulfur cycle.•Sulfate-reducing bacterialive in muddy, oxygen-poor environments like swamps. Theybreak down sulfur-containing amino acids and producehydrogen sulfide (H₂S).•Hydrogen sulfide has a strongrotten-egg smelland often accumulates in swamp mud.Recycling SulfurIn the next steps of the cycle:•Photosynthetic sulfur bacteriause hydrogen sulfide in anaerobic conditions and convert itintoelemental sulfur (S).•Colorless sulfur bacteria(such asThiobacillus,Beggiatoa, andThiothrix) further oxidizesulfur compounds intosulfate ions.Plants absorb sulfate ions and use them to make sulfur-containing amino acids, completing the cycle.1.3The Carbon CycleMost organic matter in soil comes fromdead plant material, including:•Fallen leaves•Rotting trees•Decaying rootsAnimal remains also add carbon to the soil after death.

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Study GuideRole of MicroorganismsBacteria and fungi are essential in the carbon cycle. They:•Break down proteins, fats, and carbohydrates•Recycle carbon so it can be reused by living organismsWithout this recycling, carbon would remain locked in complex molecules, and life would eventuallydecline.How Carbon Is Recycled•Microbes releaseextracellular enzymesthat digest organic matter into soluble products.•These products are then metabolized into:oCarbon dioxideoSmall organic acids (such as acetic and propionic acids)•Plants absorb these simpler compounds through their roots.Material that is not fully broken down becomeshumus, a stable and nutrient-rich part of soil.1.4The Oxygen CycleOxygen is essential forcellular respiration, including:•Glycolysis•The Krebs cycle•Electron transport and chemiosmosisTheatmosphereis the main reservoir of oxygen used in these processes.Oxygen ProductionOxygen is continuously returned to the atmosphere by:•Green plants•Photosynthetic microorganisms, such as cyanobacteriaDuringphotosynthesis, these organisms split water molecules and release oxygen as a by-product.Oxygen Use

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