Microbial Growth PDF

Microbial Growth General Microbiology, Spring 2025 When microbiologists discuss growth, they frequently mean the increase in population size after cell division; rather than a change in size of a single cell. This Not Th...

Microbial Growth General Microbiology, Spring 2025 When microbiologists discuss growth, they frequently mean the increase in population size after cell division; rather than a change in size of a single cell. This Not This Part 1: Reproduction through binary fission Describe the steps in binary fission List the other ways in which microbes can reproduce and explain what it has in common with binary fission  In binary fission, the nucleoid is replicated and divided into daughter cells DNA replication occurs. Cellular envelope enlarges. Septum grows inward as chromosomes move toward opposite ends Septum is synthesized through the cell center Two daughter cells are formed Other forms of cellular reproduction also requires replication of nucleoid Filament and spore Buddin Multiple Fission production g Part 2: Phases of Growth Curves Define batch culture Describe five phases of microbial growth Identify the phase of microbial growth based on microbial population changes Correlate environmental nutrient availability and the phases of the growth curve Calculate estimated population growth based on generation time Microbial growth is often studied through liquid culture Incubated in a closed vessel with a single batch of medium Nutrients are consumed Waste products are produced Culture flasks Culture tubes Multi-well plates Growth Curve: Population growth is plotted as a logarithm of viable cells over time Based on the growth curve, which stage of growth would you begin to see the exhaustion of nutrients? A. Lag B. Exponential C. Stationary D. Death E. Longterm stationary Lag Phase: cell number does not increase Ughh! I have no energy How do I even eat this sugar? Cells synthesize new components necessary for growth Logarithmic growth: Microbes divide at a constant maximal rate Population is uniform in terms of chemical and physiological properties. Growth rate is dependent upon multiple factors, such as nutrient availability. Stationary phase: Population growth plateaus Eww, what Nutrient limitation is that smell?!?! Accumulation of toxic Hey! Where waste products. did the food go? I don’t feel so well! Death Phase: number of cells declines exponentially Cells die at a constant rate Long Term Stationary Phase: Population size remains constant Phase can last months or years. Bacterial populations continually evolve resulting in waves of different genetic variants. Generation (Doubling ) Time: Length of time for population growth to double Tim Generatio 2n # of cell (N0 X log10N e n 2n) t T0 pop 0 0 20 = 1 1 0.000 =1 Generation (Doubling ) Time: Length of time for population growth to double Tim Generatio 2n # of cell (N0 X log10N e n 2n) t T1 pop 0 0 20 = 1 1 0.000 =2 20 1 21 = 2 2 0.301 Generation (Doubling ) Time: Length of time for population growth to double Tim Generatio 2n # of cell (N0 X log10N e n 2n) t T3 pop = 0 0 20 = 1 1 0.000 4 20 1 21 = 2 2 0.301 40 2 22 = 4 4 0.602 Generation (Doubling ) Time: Length of time for population growth to double Tim Generatio 2n # of cell (N0 X log10N e n 2n) t T4 pop = 0 0 20 = 1 1 0.000 8 20 1 21 = 2 2 0.301 40 2 22 = 4 4 0.602 60 3 23 = 8 8 0.903 Generation (Doubling ) Time: Length of time for population growth to double Tim Generatio 2n # of cell (N0 X log10N e n 2n) t T5 pop = 0 0 20 = 1 1 0.000 16 20 1 21 = 2 2 0.301 40 2 22 = 4 4 0.602 60 3 23 = 8 8 0.903 80 4 24 = 16 1.204 16 Calculate the number of cells The generation time for a bacteria is 20 minutes. If the observation begins with one bacterium, calculate how many bacteria will be present after six hours. Step 1: Calculate the number of times the bacteria will divide in six hours. Number of times per Number of doubling hour: Minutes in an times: 60 hour = 18 Number of =𝟑 generations 20 Growth Generation time time Step 2: Calculate the number of bacteria in the population. 18 1 𝑥2 =262,144 𝑐𝑒𝑙𝑙𝑠 Variation in generation times Generation times vary with microbial species and environmental conditions. It can range from less than 10 minutes to several days. You accidentally get a papercut on your finger, but you ignore it. Little did you know, bacteria entered and infected the surrounding tissue. Your finger begins to swell and eventually pus starts to form. A generation time for bacteria is 15 minutes. If observation begins with one bacterium, how many bacteria will be present in 6 hours?  Part 3: Environmental factors that affect growth  Describe the types of microbes that thrive at various temperatures.  Explain how microbes adapt to low and high temperatures.  Describe the types of microbes that thrive at various pH.  Explain how microbes adapt at different pH levels.  Describe the effects of osmolarity on microbes.  Describe ways in which microbes can adapt to high and low osmotic pressures.  Describe the different oxygen requirements for microbes.  Explain why some microbes cannot grow in the presence Microbes have a characteristic range at which growth occurs Extremophiles: Thrive in extreme conditions Microbes can grow over a range of temperatures Microbes can’t control internal temperatures Optimal temperatures depend on the enzyme activity Microbes can grow over a range of temperatures Psychrophiles Very Cold Psychrotolerants Cold Mesophiles Moderate Thermophiles Hot HyperthermophilesV ery Hot How can psychrophiles thrive in cold temperatures? A. Membranes with greater levels of saturated fats B. Membranes with greater levers of unsaturated fats Psychrophiles and psychrotolerants have adaptations that help them thrive in cold temperatures Membranes have high levels of unsaturated fatty acids Lower freezing point of cytosol Antifreeze proteins Thermophiles and Hyperthermophiles have adaptations that help them thrive in hot temperatures Saturated membranes with ether bonds Heat stable proteins with more hydrogen and covalent bonding Increase in chaperone proteins Microbes can grow over a pH range Acidophiles: Growth optimum between pH 0- 5.5 Includes many archaea, fungi, photosynthetic protists Neutrophiles: Growth optimum between pH 5.5-8 Includes most bacteria Alkalophiles: Growth optimum between pH 8- 11.5 Includes archaea, bacteria, eukaryotes An acidophile thrives in acidic pH. How can it keep its internal environment at a neutral pH? A. It takes in protons B. It removes protons from its cytoplasm Microbial adaptations to pH Acidophiles: Growth optimum between pH 0- 5.5 Includes many archaea, fungi, photosynthetic protists Transport of cations into the cell Pump protons H+ out of the cell Microbial adaptations to pH Neutrophiles: Growth optimum between pH 5.5-8 Includes most bacteria Antiport transport system to exchange potassium for protons. Pump protons out of the cell at Microbes can grow over a pH range Exchange internal Na+ for external H+ Alkalophiles: Growth optimum between pH 8- 11.5 Includes archaea, bacteria, eukaryotes Osmosis: is a form of passive transport that moves solvents from areas of high concentration to areas of low concentration Isotonic Environment Water will move into and out of the cell at a constant rate. There will be no negative effects on the cell. Osmosis: is a form of passive transport that moves solvents from areas of high concentration to areas of low concentration Hypertonic Environment Water will move out of the cell. Environment has high osmotic pressure The cell can dehydrate which may damage the plasma membrane and cause the cell to become Osmosis: is a form of passive transport that moves solvents from areas of high concentration to areas of low concentration Hypotonic Environment Water will move into the cell. Environment has low osmotic pressure This will cause the cell to burst. Osmophiles: Organisms that thrive in environments with high osmotic pressure (high solute concentrations) Halophiles: Require a salt concentration of at least 0.2M in their environments  Osmophiles: Organisms that thrive in environments with high osmotic pressure (high solute concentrations) Hypertonic Environment Halophiles: Require a salt concentration of at least 0.2M in their environments Water will move out of the cell. Environment has high osmotic pressure The cell can dehydrate which may damage the plasma membrane and cause the cell to become How can halophiles adapt to their environment? A. Increase cytoplasmic solute concentrations B. Decrease cytoplasmic solute concentrations  Adaptations of halophiles Hypertonic Environment Halophiles: Require a salt concentration of at least 0.2M in their environments Produce compatible salts, Water will move out of such as KCl, choline, betaines, the cell. and some amino acids Environment has high Accumulate K+ and Cl- in the osmotic pressure cytoplasm The cell can dehydrate which may damage the plasma membrane and cause the cell to become  Most organisms live in hypotonic environments Hypotonic Environment Adaptations Presence of a cell wall Reduce solute concentrations Mechanosensitive (MS) channels open and allow Water will move into the solutes to leave the cell. cell. Environment has low osmotic pressure This will cause the cell to burst. Microbes can neutralize ROS Superoxide free radicals: O2 - Superoxide dismutase converts free radicals into H2O2 and O2 Hydrogen peroxide: H2O2 Catalase converts peroxide into H2O and O2 Peroxidase converts peroxide into H2O  Microbes have varying oxygen requirements depending on their ability to neutralize ROS Facultative Aerotolera Microaerophi Anaerobe nt Obligate Obligate le Prefers but anaerobe Anaerobe Aerobe Requires 2- do not Grow with O2 is toxic Requires O2 10% O2 require O2 or without -SOD + SOD + SOD + SOD O2 -Catalase +Catalase +/-Catalase +Catalase + SOD - +Peroxidase +Peroxidase +Peroxidase -Catalase Peroxidase +Peroxida se You encounter an organism that has the following characteristics Membranes with high levels of saturated fatty acids No evidence of SOD or catalase Proton pumps to remove intracellular protons Increased levels of compatible salts How would you classify this? A. Psychrophile, microaerophile, acidophile, halophile B. Thermophile, facultative anaerobe, acidophile, non-halophile C. Thermophile, obligate anaerobe, alkaliphile, non-halophile D. Thermophile, obligate anaerobe, acidophile, halophile E. Psychrophile, obligate anaerobe, alkaliphile, non-halophile  Part 4: Growth in natural environments Define eutrophic and oligotrophic Describe how organisms can adapt to oligotrophic environments (endospore formation, production of starvation related proteins, growth arrest) Explain how viable but not culturable and persister cells are produced Explain how growth arrest can contribute to virulence Describe how a biofilm is made Describe ways in which microbes within a biofilm can interact with each other Explain the benefits of living within a biofilm Explain the negative effects of biofilm and medicine Nutrient requirements Eutrophic: Nutrient rich Oligotrophic: Nutrient poor/labile  Organisms can adapt to oligotrophic environments Formation of Production of Growth Arrest: endospores: proteins: Coating made of Increase Not actively dividing protein and peptidoglycan cross to conserve ATP peptidoglycan linking Inclusions for Protects of UV, Protect DNA nutrients high heat, Chaperones to Decrease cell size dessication, stabilize proteins RpoS directs mRNA chemicals transcription of survival proteins Cells that go through growth arrest Viable but not culturable Persisters (VBNC) Survive in the presence of Transient inability to grow in antibiotics previous conditions Do not have antibiotic resistance Low metabolic activity genes Still culturable Biofilms are a community of different microbes Microbes can attach and grow on surfaces Example of biofilms on teeth (dental plaque) Formation of biofilms 1. Attachment to surface via flagella and/or pili Sauer, K., Stoodley, P., Goeres, D.M. et al. The biofilm life cycle: expanding the conceptual model of biofilm formation. Nat Rev Microbiol 20, 608–620 (2022). https://doi.org/10.1038/s41579-022-00767-0 Formation of biofilms 1. Attachment to surface via flagella and/or pili 2. Production of extracellular polymeric substances Formation of biofilms 1. Attachment to surface via flagella and/or pili 2. Production of extracellular polymeric substances 3. As biofilm matures, some bacteria remain near the surface and others move outward, expanding the biofilm Formation of biofilms 1. Attachment to surface via flagella and/or pili 2. Production of extracellular polymeric substances 3. As biofilm matures, some bacteria remain near the surface and others move outward, expanding the biofilm Biofilms are heterogeneous and dynamic Made of of different microbes that interact with each other The waste products of one microbe maybe the energy source of another. Biofilms are heterogeneous and dynamic Made of of different microbes that interact with each other The waste products of one microbe maybe the energy source of another. Cells use signaling molecules to communicate Biofilms are heterogeneous and dynamic Made of of different microbes that interact with each other The waste products of one microbe maybe the energy source of another. Cells use signaling molecules to communicate Horizontal transfer of genes Biofilms are heterogeneous and dynamic Advantages: Microbes are protected from stressors such as UV light and antibiotics. This is due to both the matrix they are embedded in and the physiological changes to the cell  Biofilms and Medicine A major concern is the formation of biofilms on medical devices. They can also form on wound scabs and delay healing. Microbes can detach from the biofilm; which is of importance for medical devices since escaping cells can seed sites of infection. mling et al. 2014 – Journal of Internal Medicine