V. Soil and Plant Microbes / VI. Biofuels from Microbes

Importance of Microbes

Microbes play crucial roles in maintaining the health of natural and managed ecosystems.

Biogeochemical cycles

Processes such as the carbon and nitrogen cycles essential for ecosystem functioning.

Producers, Consumers, and Decomposers

Roles of microbes in ecosystems.

Soil Environment

A complex environment that includes physical, chemical, and biological factors.

Microhabitat level

A specific scale to consider soil environments.

Soil Organisms

Includes various micro-organisms and macro-organisms such as bacteria, fungi, and earthworms.

Microorganism distribution

Varies with soil depth and many cannot be cultured.

Microbial biomass

Estimated at 670 lb/acre of bacteria and 703 lb/acre of fungi in surface soil.

Competition among soil microbes

Intense interactions including parasitism, predation, and antibiosis.

Antibiosis

Production of antibiotics by soil microbes.

Rhizosphere

The thin layer of soil surrounding plant roots influencing nutrient availability.

Exudates

Nutrients like organic acids and sugars leached into the rhizosphere from roots.

Fungistasis

Natural prevention of fungal germination that is overcome in the rhizosphere.

Spermosphere

Soil surrounding a seed with similar nutrient dynamics to rhizosphere.

C transfer in the rhizosphere

Significant transfer of carbon from plants to soil, analogous to gut microflora.

Benefits of rhizosphere microflora

Increases nutrient availability, influences root growth, and protects against pathogens.

Symbiotic Relationships

Beneficial interactions between roots and microbes.

Parasitism

A nutritional term that is not always pathogenic.

Nitrogen-Fixing Root Nodules

Found in legumes, involving Rhizobium bacteria that fix nitrogen.

Rhizobium

Soil bacterium implicated in forming root nodules in legume plants.

Mycorrhizae

Symbiotic relationships between plant roots and fungi enhancing nutrient uptake.

Endomycorrhizae

Fungi that penetrate root cells forming arbuscules.

Ectomycorrhizae

Fungi located between root cells that take materials leached from cells.

Plant Pathogenic Microorganisms

Includes phytoplasma, nematodes, bacteria, fungi, and viruses that cause disease.

Virulence factors

Characteristics that enable pathogens to attack and damage plants.

Phytoalexins

Antimicrobial compounds produced by plants to resist pathogens.

Stomatal closure

Defense mechanism to block pathogen entry into plant leaves.

Zig-Zag Model

Explains the evolutionary arms race between plants and pathogens.

Plant Disease Resistance

Mechanisms developed by plants to defend against pathogens.

PAMPs

Pathogen-associated molecular patterns recognized by plant cells for defense.

Biofuels from Microbes

Utilization of microorganisms in producing renewable energy sources.

Biogas (Methane)

Energy produced from organic materials through anaerobic digestion.

Anaerobic digestion

Process by which microbes decompose organic matter without oxygen.

Bioethanol

Ethanol produced through fermentation, primarily from corn or biomass.

Biodiesel

Fuel from fats produced by photosynthetic organisms or engineered cells.

Lignocellulose degradation

Process important for biofuel production, involving tough plant fibers.

Termite Gut

An anaerobic environment with microflora specialized in digesting wood.

Cattle Rumen

Similar to termite gut; highlights the role of microbes in degrading plant fibers.

Volatile fatty acids (VFAs)

Energy-providing compounds produced by fermenting microbes in the rumen.

Genetic engineering in plants

Creating plants with improved disease resistance.

Medicinal antibiotics

Many come from soil-borne actinomycetes, bacteria, and fungi.

Microbial activity in rhizosphere

Intensified by nutrient input from plant roots.

Legumes

Plants such as peas and beans that form symbiotic relationships with Rhizobium.

Plant hormones

Secreted by rhizosphere microbes to influence root growth.

Chitin, Mannans, Ergosterol

PAMPs from fungal pathogens recognized by plants.

Cyanobacteria

Photosynthetic bacteria that can be used to produce biodiesel.

Metazoans

Multicellular organisms found in the soil environment.

Actinomycetes

A group of bacteria important for antibiotic production in soil.