Microbiology and Nitrogen Cycle

Bacteroids are the differentiated form of Rhizobium bacteria found within the root nodules of legumes, where they actively fix atmospheric nitrogen.

Nitrogen is absorbed from the soil as inorganic ions (nitrate/ammonium) but is also transported within the plant in organic forms like amino acids and amides.

Archaebacteria are a diverse group of prokaryotes that include methanogens, thermoacidophiles, and halophiles, which are adapted to extreme environments.

Plants cannot absorb nitrogen gas directly from the air. They rely on nitrogen-fixing bacteria, often in soil or root nodules, to convert nitrogen gas into a usable form like ammonia or nitrates.

The nitrogen cycle involves biological processes (bacteria), atmospheric processes (lightning), and human inputs (fertilizer). Rocks are primarily associated with the phosphorus or rock cycles, not the nitrogen cycle.

The primary elements that make up the biomass of microorganisms (and all living things) are Carbon, Hydrogen, Oxygen, and Nitrogen.

Nitrogen is a critical component of proteins and nucleic acids. Because it is often required in large amounts but is not always readily available in a usable form, it frequently acts as a limiting nutrient for microbial growth.

In microbiology, growth refers to the increase in the number of cells in a population, rather than the increase in size of an individual cell. This is typically measured by colony counts or optical density.

Ammonification is the process of converting organic nitrogen into ammonia, whereas nitrifying bacteria convert ammonia into nitrites and nitrates. They are distinct processes.

Rhizobium bacteria live in the root nodules of leguminous plants and fix atmospheric nitrogen into a form the plant can use.

Cyanobacteria (blue-green algae) are capable of fixing atmospheric nitrogen and are commonly used as biofertilizers in rice cultivation.

Azospirillum is a well-known free-living bacterium that fixes atmospheric nitrogen in the soil.

Azolla is a water fern that has a symbiotic association with the nitrogen-fixing cyanobacterium Anabaena azollae, which enriches the rice fields with nitrogen.

Azolla and blue-green algae (like Anabaena) are both widely used as biofertilizers in agriculture, particularly in rice cultivation.

Atmospheric nitrogen is chemically inert and cannot be used by most organisms. Lightning provides the high energy required to break the triple bonds of nitrogen gas, allowing it to react with oxygen and form compounds that reach the soil.