Bacterial Growth & Reproduction PDF

Bacterial Growth & Reproduction Varnika Kalaichelvan Department of Biosystems Technology, Faculty of Technology, University of Jaffna  Growth of Bacteria Growth may be affected by physical & nutritional factors Physical...

Bacterial Growth & Reproduction Varnika Kalaichelvan Department of Biosystems Technology, Faculty of Technology, University of Jaffna  Growth of Bacteria Growth may be affected by physical & nutritional factors Physical factors include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure & radiation Temperature: Bacteria can survive temperatures of 0° to 85°C or even more depending upon the species On the basis of temperature requirement, bacteria are divided into 3 categories viz. ❖Psychrophilic (0-30°C, opt.15°C) ❖Mesophilic (min. 5-25°C , opt. 18-45°C, max.30-50°C) ❖Thermophilic (min. 25-45°C, opt. 55°C, max. 60-93°C)  Moisture: Bacteria are more aquatic than terrestrial & can survive in presence of high percentage of water Light: Ordinary visible light does not affect bacterial activity But different spectrum of light viz UV light, infra-red light have different effect on the activity of bacterial species Pressure: Ordinary mechanical pressure can not affect bacterial cells Hydrogen-ion concentration: Suitable pH range for bacterial growth & reproduction is 5.0 to 9.0  Nutritional factor Nutritional factors include carbon, nitrogen, sulfur, phosphorus trace elements & vitamins In a liquid culture medium which has the appropriate physical & nutritional requirements, bacteria exhibit a typical growth curve Growth curve 1.Lag phase (a few minutes to several days) Bacteria are becoming accustomed or adapted to their new environment The cells are active metabolically and keep increasing in size In this phase, the bacteria do not reproduce but prepare themselves for reproduction The cells synthesize RNA, growth factors and other molecules required for cell division 2. Log phase (logarithmic) Population growth occurs at an exponential rate Growth & reproduction are most active and the generation time is reached The bacteria are sensitive to antibiotics and in humans, disease symptoms often develop during the log phase 3. Stationary phase The growth rate slows down due to a limited amount or depletion of nutrients & oxygen and an accumulation of toxic waste products from the bacteria The number of new cells produced equals the number of cells that die 4. Decline or death phase The number of cells dying exceeds the number of new cells being produced The decrease occurs at a logarithmic rate Some bacteria may form a capsule or endospores to prolong death  Which phase shows the reproduction rate equal to the equivalent death rate? a) Log phase b) Stationary phase c) Death phase d) Lag phase In bacterial growth, the growth rate slowed down due to toxic products or depletion of nutrients the resulting phase is known as ……………………………….  Bacteria reproduce asexually by binary fission & a few reproduce by budding Binary fission ❖The bacterial chromosome duplicates & the cell elongates ❖The cell wall and plasma membrane begin to grow inward at the center of the cell and separate the two chromosomes from each other ❖ Eventually the wall & the plasma membrane meet, the cell wall thickens, and the cell is divided into two identical cells  Budding ❖A small outgrowth occurs and enlarges until its size is about the same as the parent cell ❖It then separates from the parent cell  The cell reproduced by binary fission or budding continues to grow and divide & the number of cells increases geometrically With each generation produced, the population doubles When a single cell or population of cells doubles in number it is referred to as doubling time or generation time It may occur in minutes, hours, or days, but the average is 1-3 hours Eg: E. coli has a generation time of 20 minutes  Endospore Bacteria are capable of forming a range of sporulation structures but the main is endospores Most of the phytopathogenic bacteria do not produce spores Only present in some gram-positive bacteria Highly differentiated cells resistant to heat, harsh chemicals & radiation “Dormant” stage of bacterial life cycle Ideal for dispersal via wind, water, or animal gut  Endospore formation Massive sporulation occurs at the end of log phase Steps of endospore formation 1. Nuclear division -Nuclear body divided into two nuclear bodies 2. Formation of septum -On set of sporulation is marked by the formation of transverse septum -It separates the cytoplasm and DNA of the smaller cell from the rest of the cell 3. Production of fore spore The membrane of the larger cell grows around the smaller cell which becomes completely engulfed within the cytoplasm of the larger cell to produce fore spores 4. Spore maturation Cortex is deposited between the inner and outer membrane of the fore spore Spore coat is formed exterior to the outer unit membrane surrounding the cortex Eg: Bacillus subtilis: Sporulation completes in 7 hours Endospore formation  Sexual reproduction Transformation ❖Genetic material of one bacterium transform the genetic material of another Conjugation ❖Two compatible bacterial cells come into contact ❖Thus genetic makeup of both the cells is changed  Transduction ❖This process is a “phage-mediated genetic transfer” ❖Transfer of genetic material from one another via bacteriophage Q1.Transfer of genetic material from the donor to the recipient bacterium through cell contact is termed as (a) transduction (b) recombination (c) conjugation (d) Transformation Q2. Transfer of genetic material in bacteria through virus is termed as (a) transduction (b) recombination (c) conjugation (d) transformation