Microbiology and Nitrogen Cycle

Caulobacter naturally lives in dilute aquatic environment. It can grow in the medium with very low levels of carbon and nitrogen. In such minimal media, other bacteria fail to grow and caulobacter grows and produces turbidity.

Polysorbate 80 increases the growth by dispersing bacilli. It also acts as a surfactant and supplies the essential fatty acids for replication.

Some soil bacteria use organic nitrogen-containing compounds as a source of carbon, and release ammonium ions into the soil. This process is known as nitrogen mineralization.

Chemoautotrophs are organisms that are capable of manufacturing their organic food utilising chemical energy released in the oxidation of some inorganic substances. The process of manufacture of food in such organisms is called chemosynthesis. It includes some acrobic bacteria.

Rhizobium is a soil bacterium that fixes nitrogen (diazotrophs) after becoming established inside the root nodules of legumes (Fabaceae).

Nitrate reduction in plants is carried out in two steps. Nitrate is first reduced to nitrite (NO²⁻) in the cytosol by nitrate reductase using NADH or NADPH. Nitrite is then reduced to ammonia in the chloroplasts (plastids in roots) by a ferredoxin-dependent nitrite reductase. In photosynthesising tissues, it uses an isoform of ferredoxin (Fd1) that is reduced by PSI, while in the root, it uses a form of ferredoxin (Fd3) that has a less negative midpoint potential and can be reduced easily by NADPH. In non-photosynthesising tissues, NADPH is generated by glycolysis and the pentose phosphate pathway. In the chloroplasts, glutamine synthetase incorporates this ammonia as the amide group of glutamine using glutamate as a substrate. Glutamate synthase (Fd-GOGAT and NADH-GOGAT) transfer the amide group onto an 2-oxoglutarate molecule producing two glutamates. Further transaminations are carried out to make other amino acids (most commonly aspargine) from glutamine. 

Denitrifying bacteria convert nitrates and other complex nitrogen compounds back into nitrogen gas (N2), completing the nitrogen cycle. This process returns nitrogen to the atmosphere in its elemental form. Fungi, viruses, and algae do not play this specific role in nitrogen cycling.

Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with taxa such as kudzu, clovers, soybeans, alfalfa, lupines, peanuts, and rooibos. They contain symbiotic bacteria called rhizobia within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants.

Nitrosomonas nitrobacter is a chemosynthetic bacterium, which produces food material by using chemical energy, which is derived from oxidisation of certain inorganic compounds.

Diplococcus pneumoniae cause pneumonia in the host organisms. Thus, they are called pathogenic parasitic bacteria.

Clostridium botulinum is a saprophytic bacterium, which grows on dead and decaying matter.

Curd is prepared by the fermentation of milk sugar to lactic acid. Lactobacillus converts milk sugar, i.e. lactose into lactic acid.

Many legumes contain symbiotic bacteria within root nodules of their root. These bacteria have the special ability of fixing nitrogen from atmospheric, molecular nitrogen (N₂) into ammonia (NH₃) by using an enzyme called nitrogenase present in root nodules.

Digitaria belongs to the family Poaceae. Digitaria is a species of grass known by the common name hairy crabgrass or large crabgrass which has root nodules with nitrogen fixing bacteria.

Anaerobic microorganisms convert the complex substance of slurry into methane and other substances in the absence of oxygen in  a few days.