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  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

BACTERIAL GROWTH In microbiology, growth refers the “Increase number of cells”. More than 2000 chemical processes were occurred during growth. Step wise reactions occur during the growth: ü   Synthesis of the macromolecules viz ., DNA, RNA, protein, polysaccharides, lipids polymerization.  ü   Assembly of macromolecules. ü   Cell organelles formation ·       Growth rate : Increase of bacterial cell number per unit time is referred as growth rate. ·       Generation : The interval of formation of daughter cells from parental cell is called as generation. ·    Generation time : Time required to form two daughter cells from a single cell is called as Generation time.  This is also called as Doubling time. GROWTH CURVE OF BACTERIA ·       Assuming a single bacterium has been inoculated to a liquid medium and the bacterium starts multiplying by Binary fission gives increase of population. ·        The growth curve of bacteria can be divided in to 4 phases. a)      Lag