Microbial Growth (GATE)

A terminal bud forms in Hyphomicrobium species as the mother cell produces prostheca.

Being filamentous, several bacteria are chained together. It makes the determination of dry weight reasonable for enumerating bacteria. The dry weight can be correlated to the number of cells.

Some mutant E. coli often form the septum near the pole. This results in a very small daughter cell lacking DNA.

Generation time of E. coli is 17 minutes in nutrient broth at 37 degree centigrade. It is the least generation time of all the organisms given here.

G = 22.7 minutes

2 x 10¹⁰ is the right answer.
Number of bacteria = 10 x 20,000,000 x dilution factor (100)
= 2 x 10¹⁰

Cells are active in lag phase. They are rapidly synthesising new protoplasm. They are synthesising enzymes or coenzymes for operation of the chemical machinery of cell.

Caulobacter and Stella produce stalks and appendages during budding.

The most preferred method for enumeration of bacteria in milk and food cultures is viable plate count. This gives correct estimate of live bacteria in milk and food samples.

Methanopyrus kanderi is a hyperthermophile. Methanopyrus kandleri can grow within 122 degree centigrade.

Nocadazole is frequently used in cell biology laboratories to synchronise the cell division cycle. Nocadazole-treated cells enter mitosis but cannot form metaphase spindles because microtubules cannot polymerise. Thus, cell gets arrested in prometaphase.

Helmstetter-Cummings technique is used to obtain synchronous culture. In the Helmstetter-Cummings technique, a bacterial culture is filtered through a membrane. Most bacteria pass through, but some remain bound to the membrane. The membrane is subjected to reverse flow of liquid medium. The cells in the effluent stream have predominantly the characteristics of newborn cells. Hence, they are synchronous.

To reduce crab-tree effect, a fed-batch process is generally employed for baker's yeast production. Aerobic ethanol formation in the presence of glucose concentration is known as glucose effect or crab-tree effect. In this process, glucose concentration is increased in the media to reduce oxygen consumption by producing appreciable amount of ATP.

Microorganisms can be grown in a physiological steady state under constant environmental conditions in a continuous culture. In the steady state, growth occurs at a constant specific growth rate and all culture parameters remain constant.

Aerotolerant microorganisms contain superoxide dismutase but do not contain catalase. Catalase breaks toxic hydrogen peroxide to water and oxygen. These organisms can tolerate oxygen radicals due to superoxide dismutase but cannot use it for growth.