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OXIDATIVE PHOSPHORYLATION AND ELECTRON TRANSPORT CHAIN (ETC) OXIDATIVE PHOSPHORYLATION Oxidative phosphorylation is the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2  to O 2  by a series of electron carriers. This process, which takes place in mitochondria, is the major source of ATP in aerobic organisms. Oxidative phosphorylation is linked with the Electron transport chain (ETC). ELECTRON TRANSPORT CHAIN Electron transport chain (ETC) is the final common pathway in aerobic cells by which electrons derived from various substrates are transferred to Oxygen. The transfer of electrons from one electron carrier to the next releases energy, some of which is used to generate ATP from ADP through a process called Chemiosmosis. ETC is a series of highly organized Oxidation–Reduction reaction. In Eukaryotes, ETC takes place in the Mitochondria but in Prokaryotes, ETC takes place in Plasma membrane. Carrier Molecules in Electron Transport Chain (

FERMENTATION Fermentation is a metabolic process that converts the sugar to acids and gases, or alcohol. Fermentation is also used more broadly to refer to the bulk growth of microorganisms on a growth medium, often with the goal of producing a specific chemical product. French microbiologist Louis Pasteur is often remembered for his insights into fermentation and its microbial causes. The science of fermentation is known as Zymology. 1. ALCOHOLIC FERMENTATION Many fungi and some bacteria, algae, and protozoa ferment sugars to ethanol and CO 2 in a process called Alcoholic fermentation (Example Zymomonas mobilis and Saccharomyces cerevisiae ). Pyruvate is decarboxylated to Acetaldehyde, which is then reduced to Ethanol by Alcohol dehydrogenase with NADH as the electron donor. Alcoholic fermentation by yeasts produces alcoholic beverages; CO 2 from this fermentation causes bread to rise. 2. LACTIC ACID FERMENTATION Lactic acid fermentation, the reduction of pyruvate to lactate,

INDIRECT MEASUREMENT OF MICROBIAL GROWTH  1) Turbidity Estimating turbidity is a practical way of monitoring bacterial growth.  As bacteria multiply in a Liquid medium, the medium becomes Turbid, or Cloudy with cells.  The instrument used to measure Turbidity is a Spectrophotometer or Colorimeter. In the Spectrophotometer, a beam of light is transmitted through a bacterial suspension to a light sensitive Detector. As bacterial numbers increase, less light will reach the Detector. This change of light will register on the instrument’s scale as the Percentage transmission. Also printed on the instrument’s scale is a logarithmic expression called the Absorbance (sometimes called Optical density, or OD, which is calculated as Abs = 2 − log of % transmittance).  The Spectrophotometer meter has two scales. The bottom scale displays Absorbance and the top scale, Percent transmission. Absorbance increases as percent transmission decreases. The Absorbance is used to plot bacterial growth i

DIRECT MEASUREMENT OF MICROBIAL GROWTH   1) Direct Microscopic Count  A specially designed slide called a Petroff-Hausser Cell Counter is also used in Direct Microscopic Count. Petroff-Hausser Cell Counter. In the Direct Microscopic Count method, a measured volume of a bacterial suspension is placed within a defined area on a Microscope slide. Because of time considerations, this method is often used to count the number of bacteria in milk.  A 0.01 ml sample is spread over a marked square centimeter of slide, stain is added so that the bacteria can be seen, and the sample is viewed under the oil immersion objective lens. The area of the viewing field of this objective can be determined. Once the number of bacteria has been counted in several different fields, the average number of bacteria per viewing field can be calculated. From these data, the number of bacteria in the square centimeter over which the sample was spread can also be calculated. Petroff-Hausser Cell Counter Ad

  SYNCHRONOUS GROWTH Synchronous or Synchronized culture is a microbiological culture or a cell culture that contains cells that are all in the same growth stage. Synchronous growth helps studying particular stages or the cell division cycle and their interrelations. A Synchronous culture can be obtained either by manipulating environmental conditions such as by repeatedly changing the temperature or by adding fresh nutrients to cultures as soon as they enter the Stationary phase, or by physical separation of cells by Centrifugation or Filtration. An excellent and most widely used method to obtain synchronous cultures is the Helmstetter-Cummings Technique in which an unsynchronized bacterial culture is filtered through Cellulose nitrate membrane filter. The loosely bound bacterial cells are washed from the filter, leaving some cells tightly associated with the filter. The filter is now inverted and fresh medium is al

  DIAUXIC GROWTH Diauxic growth or Diauxie or Diphasic growth is the cell growth characterized by cellular growth in two phases, and can be illustrated with a Diauxic growth curve. This Diauxic growth was discovered and named Diauxie in the early 1940s by the French Biochemist Jacques Monod. Diauxic growth, meaning Double growth, is caused by the presence of two sugars on a culture growth media, one of which is easier for the target bacterium to metabolize. The preferred sugar is consumed first, which leads to rapid growth, followed by a lag phase. During the lag phase the cellular machinery used to metabolize the second sugar is activated and subsequently the second sugar is metabolized.  A simple example involves the bacterium  Escherichia coli . The Escherichia coli is grown on a growth media containing two types of sugars, one of which is easier to metabolize than the other (for example 

CONTINIOUS CULTURE OF MICROORGANISMS A Continuous culture is an Open system. The concept of the Continuous cultures dates from the 19 th Century when a continuous process for the conversion of waste Beers and Wines to Vinegar was developed. Continuous culture systems can be operated as (i) Chemostat or (ii) Turbidostat. The Turbidostat operates best at high dilution rates; the Chemostat is most stable and effective at low dilution rates. The most common Continuous culture is Chemostat. (i) Chemostat A Chemostat (from  chem ical environment is  stat ic) is a Bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms are continuously removed at the same rate to keep the culture volume constant. In Chemostat, both Growth rate and Cell density can be controlled independently. ü   Growth rate - How fast the cells divide. ü   Cell density - How many cells per ml are obtained.        Tw

FACTORS INFLUENCING BACTERIAL GROWTH A) SOLUTE AND WATER ACTIVITY (i) Osmotolerant ·        Able to grow over wide ranges of water activity or osmotic concentration. ·        Example - Staphylococcus aureus. (ii) Halophile ·        Requires high levels of sodium chloride, usually above about 0.2 M to grow. ·        Examples - Halobacterium, Dunaliella and Ectothiorhodospira. B) pH (i) Acidophiles ·        Grow optimum between pH 0 to 5.5. ·        Examples - Sulfolobus, Picrophilus, Ferroplasma, Acontium and Cyanidium caldarium (ii) Neutrophiles ·        Grow optimum between pH 5.6 to 8.0. ·        Example – Escherichia coli. (iii) Alkalophiles ·        Grow optimum between pH 8.1 to 11.5. ·        Examples – Bacillus alcalophilus and Natronobacterium .   C) TEMPERATURE (i) Psychrophiles ·        Grows well at 0 °C and has an optimum growth temperature of 15 °C or lower. ·        Examples - Bacillus psychrophilus (ii) Psychrotrophs ·        Can grow at 0 – 7 °C; has an optimum betwee