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by: Cassie Koepp


Cassie Koepp
GPA 3.61

K. Sullivan

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K. Sullivan
Class Notes
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This 10 page Class Notes was uploaded by Cassie Koepp on Tuesday October 13, 2015. The Class Notes belongs to BIOL 2051 at Louisiana State University taught by K. Sullivan in Fall. Since its upload, it has received 12 views. For similar materials see /class/222793/biol-2051-louisiana-state-university in Biological Sciences at Louisiana State University.

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Date Created: 10/13/15
Chapter 5 Environmental Influences and Control of Microbial Growth Environmental factors that affect microbial growth 0 Temperature 0 Pressure 0 Osmolarity 0 pH 0 Oxygen Temperature Temperature is a major environmental factor controlling microbial growth cardinal temperatures minimum optimum amp maximum temps for an organism minimum temperature cellular processes slow down cytoplasmic membranes stiffen Maximum temperature proteins start to denaturecannot work anymore Optimum temperature organism grows best between min amp max Microorganisms can be grouped by the temperature ranges they require Psychrophiles Grow best at Cold O C 20 C Mesophileswhich are temperature that are comfortable to us things that grow in our environment are mesophiles 20 C 45 C thermophiles 40 C 80 C Extreme thermophiles 65 C 113 C which is above boiling Psychrophiles found in constantly cold environments Example Chlamydomonas llsnow algae pink algae that grows on snow Molecular adaptations of psychrophiles Membranes have high content of unsaturated fatty acids semifluid at low temperatures so transport can occure correctly Proteins are more flexible compared to mesophiles or thermophiles Cryoprotectants can be used to preserve microbial cultures at low temperatures 10 Dimethylsulfoxide amp 10 glycerol are commonly used in laboratories to preserve microbial cultures for long time in freezers Mesophiles Found in warm blooded animals amp many terrestrial amp aquatic environments Examples most organisms you are familiar with such as Escherichia coli found in the Thermophiles Optimum temp above 40 degrees C Some Archaea have been found growing at temps above Places thermophiles are found 0 soils subjected to full sunlight like a dessert soil 0 fermenting materialscompost piles 0 Hot Springs Thermus aquaticus is a common hot spring thermophile The heat stable DNA polymerase from this bacterium is mass produced and used in laboratories to replicate DNA in a test tube Molecular adaptations of thermophiles o Membranes have a high content of saturated fatty acidsstable and functional at high temperatures 0 Enzymes are heat stable protiens are more rigid compared to mesophiles or psychrophiles I Heat shock response 0 Occurs at high end of temperature range 0 Emergency proteins produced 0 Help keep proteins from denaturing o Induced by many stressful conditions Heat High salt concentrations Arid conditions Pressure 0 Adapted to live at very high pressures Up to 1000 atm like ocean floor Barotolerant organisms o Grow at high but not very high pressure Barosensitive organisms 0 Die at high pressure Most typical bacteria all mammals Osmolarity 0 Water moves from areas of high water concentration to areas of lower water concentration 0 Water moves from areas of low solute concentration to areas of high solute concentration 0 The diffusion of water is called osmosis q ln a h otcimc In a hypertonic environment emtlromllllen water will move out Waterw39 rl lwve a cell amp the cell will Lee 39 Die from Iasmol sis look HQ In a hypotonic environment the cell wall of most prokaryotes prevents too much water from entering cells even if equilibrium is never reached lsotonic equal amount of soluteswater on inside amp outside of cells However there is no physical barrier that prevents cell from losing too much water if cell is in hypertonic environment 0 Some cells can increase solute concentration in cell to prevent to much water loss by 1 pumping inorganic ions K into the cell 2 Making or concentration an organic solute glycerol in the cell Osmophile organism that grows in high solute concentrations hypertonic environments Halophilesgrow best in high salt habitat 7 Vibrio lives in ocean salt in ocean About 35amp salt Extreme halophiles m high levels 15 to 30 of salts for growth 7 Halobacterium salinarium requires 25 salt lives in very salty lakes Halotolerant Can survive salt at higher salt concentrations but grow best in absence of 7 Staphylococcus pH relative hydrogen ion concentration in a solution Scale is from O to 14 7 is neutral lt 7 is acidic gt 7 is basic Most bacteria grow at pH of 68 Bacteria can be found to exist at almost any pH Most cells internal pH remains near 7 regardless of pH of their environment Most organisms have a pH range at which they can grow of 23 pH units Acidity or alkalinity of an environment can greatly affect microbial growth Weak acids can pass through cell membranes Good food preservatives Classification based on optimal pH Some organisms have evolved to grow best at low or high pH but most organisms grow best between pH 6 and 8 and are called neutralophiles neutrophiles Acidophiles grow best at low pH I Stability of CM is critical since increases in pH can cause lysis I Ex Many fungi Thiobacilus produces sulfuric acid volcanic thermal soil archaea Picrophius oshimae grows optimally at pH 07 Alkalophiles grow best at high pH I found in soda lakes amp high corbonate soil I Many species of Bacillus live in very alkaline soils I Bacillusfirmus has a pH range of 7511 I Proteases and lipases made by alkaliphiles are mass produced amp used in household detergents Oxygen Microorganisms vary in their need or tolerance of oxygen 02 amp can be grouped based on their requirements for 02 oxic environment environment in which oxygen is present anoxic environment environment in which no oxygen is present Aerobes use 02 to generate energy by respiration Facultative aerobes use Oz in respiration but can also grow in anoxic environment Ex Streptococcus mutans on teeth 39 E coi in large intestine Obligate aerobe use Oz in respiration amp reguire oxic environments for growth Grow at atmospheric oxygen levers 21 Ex Micrococcus luteus Microaerophile use Oz in respiration but require low oxygen concentrations 210 microoxic environments to gorw Ex Streptococcus pneumonia 0 Anaerobes cannot use 02 in respiration and many be inhibited or killed by oxygen Aerotolerant anaerobes do not use 02 to generate energy but can survive in presence of it Ex Streptococcus pyogenes Obligate anaerobes can only grow in anoxic environments may die if even minute amount of 02 is present Ex Clostridium sporogenes Bacteroides in large intestine A reducing agent can be added to a medium to test an organism s requirement for oxygen Thioglycolate reacts with oxygen reducing it to water In a culture medium thioglycolate will convert all Oz to water only top of culture is exposed to 02in the air 0 The position of the bacteria within these thioglycolate broth cultures reveals the Oz requirements for each of the bacteria Special techniques are needed to grow aerobic amp anaerobic microorganisms in the laboratory Aerobes culture medium must be oxygenated by shaking or bubbling air into the medium 0 Anaerobes need Oz to be excluded 0 Bottles or tubes can be filled completely with media and sealed with a screw cap 0 Reducing agents thioglycolate can be added to convert all Oz to water 0 Anoxic 39ars with a palladium catalyst convert oxygen to water 0 For obligate anaerobes that die if exposed to oxygen media must be boiled a reducing agent added then sealed infer an oxygen free H2 or N2 gas 0 Work with these cultures must be done in an anoxic environment that can be provided by anoxic glove boxes 0 Toxic Forms of Oxygen Several toxic forms of oxygen or molecules that contain oxygen can be formed in the cell during normal cellular processes all of thesis are generated during the reduction of oxygen to water Singlet oxygen 102 produced by peroxidases Superoxide anion 02 Hydrogen peroxide H202 Hydroxyl radical OH Enzymes made by cells can neutralize toxic forms of oxygen 0 Catalase peroidase superoxide dismutase superoxide reductase Controlling Microbial Growth Physical Agents Temperature 0 Pasteurization 63 C for 30 minutes 0 Flash pasteurization 72 C for 15 seconds does NOT kill all cells that are present reduces microbial load of viable organisms kills most pathogens inhibits spoilage microbes 0 U HTUltrahigh temperature 150 C for 3 seconds Sterilizes al bacteria killed creamer boxed milk Physical Agents Temperatu re Pressure 0 Autoclave Large sealed device that sterilizes things How long you put it in there depends on the volume 121 C 15 psi 20 min Kills all bacteria things that come out are sterile Destroys endospores Physical Agents Other Methods 0 Cold temperature Refrigeration Doesn t sterilze So microorganisms are still in there reproducing but they are doing it a lot slower When you take out of freezer and in sink once it gets to room temp micrs reproduce very quickly Freezing Slows growth does not kill all bacteria o Irradiation Microwaves thermal effects 0 So the microwave doesn t kill the microbacteria it s the heat in the microwave that kills them Ultraviolet radiation DNA damage 0 These are ionizing radiation 0 Casues nulclec acid and protein damage 0 Very dangerous Xrays Gamma rays Ultraviolet radiation used to decontaminate surfaces and materials that do not absorb light air and water Causes thymine dimmers Ask what does that mean in DNA If enough of these prevents the DNA from replicating and the organisms cell dying UV hood air is blown outward through a filter from the back and from edges of the hood so that the area inside the hood remains sterile once the UV light is turned off lonizing radiation Gamma rays amp Xrays penetrates solid surfaces or light absorbing material so pretty much anything an be sterilized by this widely used for sterilization amp decontamination treatment of an object or surface to make it safe to handle in medical and food industries Causes breaks in DNA breaks hydrogen bonds amp disulfide bridges in proteins l Green symbol that means that item has mean sterilized by ionization o Filtration Filterdevice with pores too small for microorganism to fit though but large enough for liquid or gases to pass through Filters remove microorganisms from air or liquids that are heat sensitive 2 types depth amp membrane Depth filters fibrous sheets or mats made from a random array of overlapping paper asbestos or borosilicate traps large particles from liquids and air Examples HEPA filters Some vacuums Home air conditioning blue thing Home airheat system Vacuum cleaner UV hood Clean rooms and isolation rooms for quarantine Membrane filters thin sheets of polymers cellulose contain tiny holes of known size Act like sieves trap particles on membrane surface Antibiotics amp other pharmaceuticals Nucleation track Nucleopore filters used for concentrating a liquid sample for view on the scanning electron microscope Chemical Agents Disinfectants used to reduce microbial numbers on nonliving material bleach chlorine ethanol Antiseptics used to reduce microbial numbers on living tissues Betadyne iodine H202 Anything you out on a cut or sore o Antibiotics Naturally occurring antimicrobial substances produced by microorganisms Many known but less than 1 clinically useful because of poor uptake or toxicity Selectivier kills microbes May not work on all species Good and bad bc may kill things that don t need to be killed lnterferes with bacterial specific enzymes Cell wall synthesis l lnhinbits cross linking in peptidoglycan l Doenst hurt us bc no cell wall no pepto Bacterial ribosome l Our ribosomes very diff them prokaryotes so it wont hurt us Penicillin Many derivatives Blocks cell wall synthesis prevent crosslinking of peptidoglcan cell wall Growing bacteria lyse l Slowgrowing bacteria take longerto die Biological Agents 0 Probiotics llGood bacteria Displace pathogens from tissues Found in yogurt Keep area full of good bacteria so pathogens cannot grow 0 Bacteriophage Phage Viruses that infect bacteria Do not harm eukaryotes


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