Bacterial Growth Lecture Notes

Bacterial growth: Growth- increase in the number of cells Bacterial reproduction can occur in several ways including: Binary fission: Occurring most in commonly encountered bacteria when cell enlarges & divides into 2 Budding: Small projections at the end of the cells which enlarge i.e. rhodopseudomonas acidophila Filamentous growth: Cells fragment into smaller units i.e. nocardia spp. Expospore formation: External spores formed at the hyphae tips i.e. streptomyces species Binary fission: Due to the lack of nuclei, mitosis/meiosis cannot occur so they undergo binary fission instead. The original single chromosome is duplicated and with 2 copies, the cell can elongate to 2 separate chromosomes. Between the 2 copies of chromosomes, a septum begins to form by pinching in gram +ve and growin in gram -ve. Once the septum finished forming and divides the one bacterium into 2 be3coming separate 2 daughter bacteria. Prokaryote cell division: Some proteins essential for division are filamentous temperature sensitive Fts which interact to form divisome. This occurs when FtsZ form a ring around the cell centre. There are ma ny Fts proteins attracted to the ring. Autolysins digest peptidoglycan that is already pre-existing and beginning at FtsZ ring The divisome synthesis’s new cytoplasmic membrane Batch culture bacterial populations growth: 4 phases involved in this i.e. in liquid medium 1)lag phase 2)log phase 3)stationary phase 4)death phase " Lag phase: A delay in growth once a microbial population is inoculated to fresh media and this delay is dependant on growth phase of initial inoculum, viability of initial inoculum and the type of medium This is with little or no cell division whilst there is acclimatisation to new conditions however, this is the period of maximum cell enlargement to. Get ready for division, synthesis of DNA, ribosomes and enzymes The cells are moderately resistant to toxic agents Exponential phase: During exponential growth, this is the healthiest state of a cell and as long as the essential nutrients are present, the cells will all continue to divide rapidly This division rate is dependant on environmental factors i.e. temperature and this is when the cells are most sensitive to toxic agents Generation: one cell becomes 2 daughter cells Generation time/ doubling time: time it takes for one generation to occur Generation time can be anywhere between 1 & 3 hours but for E-coli 20 minutes Stationary phase: Limiting factors include the lack of essential nutrients and the accumulation of waste products This inhibits exponential growth from continuing and cells enter this stationary growth phase, there are no net movement increase of decrease in cell numbers Death phase: The cells begin to die and cell lysis can occur, this phase occurs exponentially but still slower than the exponential phase The growth of bacteria populations aim to eliminate the maximum stationary phase by removing the causes and is often within the fermentation processes in the industry 1)unlimited supply of nutrients 2)growth vessel with services 3)constant head device collector The growth rate is controlled by limiting an essential nutrient or chemostat Microbial cell growth can be measured by 1) total cell count 2) viable cell count 3) microbial mass Total cell count: A microscope is used to count all cells both live and dead on dried samples on a slide or liquid samples using a counting chamber i.e. haemocytometer However, this does not distinguish from live and dead, the small cells may be difficult to count, this is not suitable for low cell density samples and most cells must be immobilized Viable cell counts or plate counts: The measurement of living and reproducing population This can be performed by spread-player methods and pour-plate methods to obtain the appropriate colony number in which the counted sample should always be diluted However, the colony number can alter the length of incubation, there may be pipetting errors and also cell clumping Count plates versus microscopic count- reasons for anomalies may e due to microscopes counting both dead and living cells, different nutritional requirements or culture conditions Microbial mass: Turbidimetric method is useful during the exponential growth for measuring the mass of increased protein, DNA, dry weight or culture. Optical density measured using a spectrophometer. A standard curve must be produced in order to link absorb acne readings to direct counts 260nm DNA, 280nm protein, 600nm cultures Biofilms: May produce self defence, allowing cells to remain in a favourable niche and to live in close association, a typical way bacterial cells grow in nature Bacterial cells require certain nutrition such as carbon, nitrogen, phosphorus, sulphur, potassium, magnesium, sodium, calcium, iron Selective media contains inhibiting growth compounds of specific microorganisms bout differential media is an indicator used i.e. dye to distinguish between different metabolic and chemical reactions in organisms