(Q) Which of the following phases of the bacterial growth curve is matched with the correct definition? Answer: (2) log phase–the phase where organisms are actively dividing and the generation time is constant.

Many studies require the quantitative determination of bacterial populations. The two most widely used methods for determining bacterial numbers are the standard, or viable, plate count method and spectrophotometric (turbidimetric) analysis.

Spectrophotometry is an indirect method for calculating cell concentrations by measuring the changes in turbidity. Bacteria can also be counted by using the plating method, which is based on the number of colonies formed in Petri dishes containing specific growth media.

The rate of exponential growth of a bacterial culture is expressed as generation time, also the doubling time of the bacterial population. Generation time (G) is defined as the time (t) per generation (n = number of generations). Hence, G=t/n is the equation from which calculations of generation time (below) derive.

Microbiology

There are three phases of growth – meristematic, elongation and maturation.

Pathogenic strains of bacteria tend to grow faster than non-pathogenic strains at 37°C, so researchers may set incubators at 25°C to restrict its growth. When given an unknown bacterial sample the first step is to expand the current bacterial population.

What is the key difference between photoheterotrophs and photoautotrophs? Photoheterotrophs use organic compounds as their carbon source; photoautotrophs use carbon dioxide as their carbon source.

Examples of phototrophs/photoautotroph include:

• Higher plants (maize plant, trees, grass etc)
• Euglena.
• Algae (Green algae etc)
• Bacteria (e.g. Cyanobacteria)

Synechococcus elongatus

“Chemoheterotroph” is the term for an organism which derives its energy from chemicals, and needs to consume other organisms in order to live. Animals and fungi both, for example, obtain energy by breaking down our food, and also get the building materials for our own cells from the food we eat.

Noun. photoorganoheterotroph (plural photoorganoheterotrophs) (biology) A organoheterotroph that also obtains energy from light.

Some examples of chemoautotrophs include sulfur-oxidizing bacteria, nitrogen-fixing bacteria and iron-oxidizing bacteria. Cyanobacteria are included in the nitrogen-fixing bacteria that are categorized as chemoautotrophs.

Iron bacteria, Ferrobacillus- They derive energy by oxidizing dissolved ferrous ions and are chemoautotrophs.

Chemotrophs obtain their energy from chemicals (organic and inorganic compounds); chemolithotrophs obtain their energy from reactions with inorganic salts; and chemoheterotrophs obtain their carbon and energy from organic compounds (the energy source may also serve as the carbon source in these organisms).

Escherichia coli :- it is a heterotrophic organism that depends on others for food. They obtain their food from the host organism . They obtain food by following the biosynthetic organic pathway. Rhizobium :- it lives inside the root nodules of leguminous plants.

Rhizobium is a genus of bacteria associated with the formation of root nodules on plants. These bacteria live in symbiosis with legumes. They take in nitrogen from the atmosphere and pass it on to the plant, allowing it to grow in soil low in nitrogen.

Rhizobia (the fast-growing Rhizobium spp. and the slow-growing Bradyrhizobium spp.) or root nodule bacteria are medium-sized, rod-shaped cells, 0.5-0.9 ~m in width and 1.2-3.0 ~m in length. They do not form endospores, are Gram-negative, and are mobile by a single polar flagellum or two to six peritrichous flagella.

Rhizobia are a “group of soil bacteria that infect the roots of legumes to form root nodules”. Rhizobia are found in the soil and after infection, produce nodules in the legume where they fix nitrogen gas (N2) from the atmosphere turning it into a more readily useful form of nitrogen.

Rhizobium–legume symbioses are of great ecological and agronomic importance, due to their ability to fix large amounts of atmospheric nitrogen. These symbioses result in the formation on legume roots of differentiated organs called nodules, in which the bacteria reduce nitrogen into ammonia used by the host plant.

They fix atmospheric nitrogen into an organic form which is then used by plants as nutrients. Rhizobium can be used as a biofertilizer. They fix atmospheric nitrogen into an organic form, which is used by the plants as nutrients.

IMPORTANCE Rhizobia are soil bacteria best known for their capacity to form root nodules on legume plants and enhance plant growth through nitrogen fixation.

Rhizobium is a vital source of nitrogen to agricultural soils including those in arid regions. They convert dinitrogen into ammonia. Ammonia, being toxic in nature. is rapidly absorbed into organic compounds. Nitrogen fixation helps in increasing soil productivity and soil fertility.

Soil bacteria belonging to the genus Rhizobium induce symbiotic nitrogen-fixing nodules on the root of their leguminous host plants. This bacterium-plant interaction is highly specific.

Among the 5 species of the genus Rhizobium, R. radiobacter is the only one known to cause human disease, though it has a low virulence for humans [3, 4]. It is a rare opportunistic organism in human infections, which was never reported isolated in infected nonunions.

Rhizobium bacteria are found in the root nodules of leguminous plants.