NU BIOL 1121 - CHAPTER 4: Prokaryotic Growth

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CHAPTER 4: Prokaryotic Growth Principles of Prokaryotic Growtho Divide by binary fission  Increased in size and doubled its components This attributes to bacteria ability to grow exponentially o Microbial growth Used to discover the relative size of cells in a given population Defined by the number of cells in a populationo Generation (doubling) time The time it takes for the population to double in number  Varies on the species and the conditions of the environment  E. coli is approx. 20 minutes, while Mycobacterium is about 12 hourso Calculating the doubling time Nt = No + 2n Where Nt is the population at a give ntime (t) and No is the initial population N is the number of cell divisions Bacteria Growth in Natureo Natural and the laboratory growing environments differ greatly Ex: a type of prokaryote may create slime layer to attach to rocks in nature, but not in the labo Biofilms Can live suspended in an environment, but attach to surfaces as well Attach by creating a polysaccharide layer while living in communities Biofilm forms when planktonic, free floating bacteria adhere to a surface where they multiply and synthesize slime layers to which unrelated cell may attach and grow Slime layers have characteristic open channels through which nutrients and waste can pass Cells communicate by synthesizing and responding to chemical signals (an exchange that is important in establishing structure) 65% of bacterial infections result from biofilms- cystic fibrosis, dental plaque and ear infections- able to resist antibiotics well because of the protective slime layer  help sewage degradation and bioremediation are enhaced with biofilm planktonic vs. same species in a biofilm (much more resistant)o Interactions of mixed microbial communities Prokaryotes other grow in the presence of other microbes  Can be hospitable to each other (foster bacteria that otherwise would not survive)- Ex: one bacteria’s waste could be another’s food source- Anaerobes that cannot grow with o2 can grow in the mouth because other bacteria consume the o2 Can be non hospitable- Can create toxins that kill off competetorsObtaining a pure cultureo Pure culture A colony of cells where each cell is similar (same species) Easier to study, but do cells in pure cultures may not bahave as they do naturally Only 1% can actually be grown in the lab In order to cultivate need: sterile (all microbial growth killed), aseptic techniques (procedures that minimize the chance of other organisms being introduced), and a culture medium (a medium that hasthe nutrients that will encourage cell growth)o Cultivating Bacteria on a Solid Culture Medium Requirements: solid culture medium, a media container that can be maintained in an asceptic condition, and a method to separate bacteria cells  A single bacterium, will multiply to form a colony: or pure culture Agar: a polysaccharide extracted from marine algae - Used to solidify a liquid culture medium- Unlike other gelling agents (gelatin) agar stays solidified at room temp- Not destroyed at high temperatures- Nutrients that would be destroyed at high temperatures are added at lower temps (preserving)- Remains solid (95 degrees C) at the temp which most microbes grow Petri dish: the two-part container made of glass or plastic, excludes airborne microbes Agar plate: Petri dish filled with Agaro Streak plate method Simplest and most commonly used technique for isolating bacteria A sterilized inoculating loop is dipped into microbial containing solution Parallel streaks, that reduces along each quadrant o Maintaining stock cultures Stock culture: a culture derived from a pure colony that is stored for use in later inoculum procedures- Stored in fridge in an agar slant (a tube held at a shallow angle as the medium solidifies) creating a larger surface area- Lyophilized; freeze driedBacterial Growth in Laboratory Conditions o Closed or batch systems Systems without renewing nutrients or any mechanism ofwaste removal  Agar, tubes, or flasks Cell number increases in a predictable fashion and theneventually declines Follows a particular growth curve  Most distinct in a broth culture because exposed to thesame conditions as planktonic particleso Open system Needed to maintain continuous growth of a culture Nutrients are added and waster products are removedo The Growth curve Lag phase- When the bacteria are diluted and transferred need time for considerable growth- Lag phase: a “tooling up” prior to multiplication- Synthesize macromolecules (ribosomes, nucleic acids, ATP)- The length deepens on the species and the conditons - Less nutrients = more time because need to synthesize the missing nutrients  Exponential Phase (Log phase)- Cells divide at a constant rate and their numbers increase by the same percentage each tiem interval- The generation time is based on this time of active multiplication- Most susceptible to antibiotics during this time (laying down peptido)- Activities are directed towards increasing cell masso Produce amino acids, nucleotides,and building blocks of proteinso Ability to precisely regulate theseamounts to ensure for efficientassembly- Primary metabolites: compounds synthesized duringthis phaseo A product of any rxn that isessential for growth o Can be used as flavoring - Late log phaseo A shift in cell activityo Nutrient depletion and waste build up cause the system to enter stationary phase o If endospores, initiate sporulation during this phase o Become rounder, and more resistant to chemicals & radiationo Composition of cell wall and membrane may occuro Synthesize secondary metabolites These can be antibiotics, which kill off other microbes Stationary phase- No longer have supplies or energy to sustain adequate growth- Population remains constant (some die as other multiply)o Cells that dies release their components that can stabilize other bacteria- Cells continue to synthesize secondary metabolites and maintain altered properties of late logstage Death phase- Total number of viable cells die off at constant rate- Dies off slower than it multiplies Phase of prolonged decline (dynamic process)- Marked by a very gradual decrease in the number of cells - Very long phase- Cells die and other cells use components, constant pop fluxo Colony Growth Same as liquid, but after lag grow and compete for nutrients The


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