Microbiology Chapter 9: Microbial Growth PDF

MICROBIOLOGY Chapter 9 MICROBIAL GROWTH PowerPoint Image Slideshow  BIOFILMS In nature most microorganisms exist in communities attached to surfaces known as biofilms. The electron micrograph (left) shows the inside walls of an in-dwelling catheter. The garbage can (right) served as a rain...

MICROBIOLOGY Chapter 9 MICROBIAL GROWTH PowerPoint Image Slideshow  BIOFILMS In nature most microorganisms exist in communities attached to surfaces known as biofilms. The electron micrograph (left) shows the inside walls of an in-dwelling catheter. The garbage can (right) served as a rain collector. The arrow points to a green biofilm on the sides of the container. (credit left: modification of work by Centers for Disease Control and Prevention; credit right: modification of work by NASA) BINARY FISSION Prokaryotes undergo asexual reproduction. This results in genetically identical daughter cells (unless a mutation occurs). This pattern of reproduction is exponential. FIGURE 9.4 The parental cell divides and gives rise to two daughter cells. Each of the daughter cells, in turn, divides, giving a total of four cells in the second generation and eight cells in the third generation. Each division doubles the number of cells. FIGURE 9.5 FIGURE 9.6 Both graphs illustrate population growth during the log phase for a bacterial sample with an initial population of one cell and a doubling time of 1 hour. (a) When plotted on an arithmetic scale, the growth rate resembles a curve. (b) When plotted on a semilogarithmic scale (meaning the values on the y-axis are logarithmic), the growth rate appears linear. DOUBLING TIME The generation (doubling) time is the amount of time for the population to double in number. The equivalent of one round of division for every cell. This number can vary greatly based upon two factors; 1. The type of species; different metabolic capabilities 2. The environmental conditions; the same type of organism in optimal vs suboptimal conditions will not reproduce at the same rate If we know the generation time of an organism or can determine it then we can make predictions about how many bacteria will be in a sample in the future or were present in the past.  PRACTICE Time Log CFU cells 0 1 10 1 1 10 2 1 10 3 1.60206 40 4 2.20412 160 5 2.80618 640 6 3.40824 2560 7 4.0103 10240 A sample of bacteria was spiked into sterile room temperature apple juice. Bacterial numbers were assessed every hour for seven hours. Explain what you are seeing in the graph and answer the following: 1. How many cells is equivalent to 1 log CFU on the graph? 2. What is the generation time of this organism? 3. How many cells are predicted for the 10 hour mark? 4. Would the rate of increase be higher or lower if the apple juice were incubated at human body temp? QUANTIFICATION METHODS What are some hurdles to counting the number of bacteria in a sample? A number of methods may be used either by Direct counting of cells or colonies or Indirect calculations based on evidence of bacterial growth. DIRECT MICROSCOPIC COUNT A Petroff-Hausser chamber is a special slide designed for counting the bacterial cells in a measured volume of a sample. A grid is etched on the slide to facilitate precision in counting. (credit a: modification of work by Jeffrey M. Vinocur) DISTINGUISHING LIVING FROM DEAD Fluorescence staining can be used to differentiate between viable and dead bacterial cells in a sample for purposes of counting. Viable cells are stained green, whereas dead cells are stained red. (credit: modification of work by Emerson J, Adams R, Bentancourt Román C, Brooks B, Coil D, Dahlhousen K, Ganz H, et al.) PLATE COUNT TECHNIQUES Serial dilution involves diluting a fixed volume of cells mixed with dilution solution using the previous dilution as an inoculum. The result is dilution of the original culture by an exponentially growing factor. (credit: modification of work by “Leberechtc”/Wikimedia Commons) SPREAD PLATE Quantitative plate count methods are the most commonly used means of assessing the concentration of a bacterial population. FIGURE 9.14 In the most probable number method, sets of five lactose broth tubes are inoculated with three different volumes of pond water: 10 mL, 1 mL, and 0.1mL. Bacterial growth is assessed through a change in the color of the broth from red to yellow as lactose is fermented. INDIRECT METHODS A spectrophotometer is commonly used to measure the turbidity of a bacterial cell suspension as an indirect measure of cell density. (credit a: modification of work by Hwang HS, Kim MS; credit b “test tube photos”: modification of work by Suzanne Wakim) BIOFILMS Stages in the formation and life cycle of a biofilm. (credit: modification of work by Public Library of Science and American Society for Microbiology) https://www.youtube.com/watch?v=Ivy0_Y7q-6M QUORUM SENSING https://europepmc.org/article/med/26542036 Communication within bacterial biofilms or populations in a culture is possible through the use of quorum sensing. Autoinducers are chemicals secreted by cells that elicit a change in gene expression once a threshold is reached; i.e. when the population is large enough GROWTH CONDITIONS Imagine you were provided with an environmental sample containing bacteria. Your job is to get the bacterium to grow in vitro on a petri dish. Brainstorm the different conditions you would need to provide when attempting to supply the needs of this “mystery” organism. Growth Parameters  MOLECULAR OXYGEN Two factors contribute to a bacterium’s ability to grow in regards to oxygen: 1. The metabolic capabilities of the bacterium; some can only ferment other cannot respiration 2. The ability to synthesize enzymes that can detoxify harmful reactive oxygen species (ROS) FIGURE 9.23 The catalase test detects the presence of the enzyme catalase by noting whether bubbles are released when hydrogen peroxide is added to a culture sample. Compare the positive result (right) with the negative result (left). (credit: Centers for Disease Control and Prevention) FIGURE 9.21 (a) An anaerobic jar is pictured that is holding nine Petri plates supporting cultures. (b) Openings in the side of an anaerobic box are sealed by glove-like sleeves that allow for the handling of cultures inside the box. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by NIST) PH Most bacteria tend to fall in the neutrophile category while acidophiles and alkaliphiles are most likely found in very specific environments. What do you remember about the effects of changing pH on cellular activity? FIGURE 9.25 Lactic acid bacteria that ferment milk into yogurt or transform vegetables in pickles thrive at a pH close to 4.0. Acidic foods have been a mainstay of the human diet for centuries, partly because most microbes that cause food spoilage grow best at a near neutral pH and do not tolerate acidity well. (credit “yogurt”: modification of work by “nina.jsc”/Flickr; credit “pickles”: modification of work by Noah Sussman; credit “sauerkraut”: modification of work by Jesse LaBuff; credit “pico de gallo”: modification of work by “regan76”/Flickr) FIGURE 9.27 View from space of Lake Natron in Tanzania. The pink color is due to the pigmentation of the extreme alkaliphilic and halophilic microbes that colonize the lake. (credit: NASA) TEMPERATURE The graph shows growth rate of bacteria as a function of temperature. Notice that the curves are skewed toward the optimum temperature. What happens to cells when temperatures rise above optimal? FIGURE 9.28 A black smoker at the bottom of the ocean belches hot, chemical-rich water, and heats the surrounding waters. Sea vents provide an extreme environment that is nonetheless teeming with macroscopic life (the red tubeworms) supported by an abundant microbial ecosystem. (credit: NOAA) OSMOTIC PRESSURE Environmental solute concentrations can have a significant osmotic effect on prokaryotes. What happens when a cell finds itself in a hypertonic solution? Hypotonic? Most terrestrial and freshwater microbes live in hypotonic environments some may be able to tolerate higher levels of salt or solute. They are referred to as halotolerant. Bacteria and Archaea that live in the ocean or salt lakes typically require high osmotic pressure and are halophilic. BACTERIAL GROWTH MEDIA All living things share a common need for certain elements to perform their metabolic functions. Take a moment to brainstorm the main biological molecules that make up a cell. What elements are they composed of? How do heterotrophs like us acquire them? What about autotrophs? https://www.chromagar.com/en/product/chromagar-esbl/ COMPLEX VS DEFINED https://www.grainger.com/ Which of the above ingredient lists would be complex and which is chemically defined?  SELECTIVE AND DIFFERENTIAL The metabolic pathways available to many bacteria allow them to build everything they need from a source of carbon and energy (like glucose) and basic minerals. Other “fastidious” organisms have special nutritional requirements. Additional ingredients may be added to assist in growing certain organisms. Selective media- inhibit unwanted organisms Differential media- change colors in the presence of the growth of certain species This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted.