Chapter 6 What do microorganisms generally need to grow Nutrients Materials to make cell parts Energy source Electron flow to drive all life processes Drives ions into out of cells Used for chemiosmosis to create ATP Glucose is a great nutrient source carbon source energy source Nutritional requirements of microorganisms Acquisition of nutrients Carbon large amount needed by cells to form organic compounds amino acids fatty acids sugars nucleic acids to carry out cellular functions An organic compound has carbon hydrogen bonds so carbon dioxide is not organic Glucose is an organic compound Carbon is a macromolecule Autotrophs assimilate carbon from inorganic sources can use CO2 as a sole carbon source Plants are autotrophs and so are many bacteria Heterotrophs assimilate carbon in preexisting organic form must have organic compounds most prokaryotes and all other organisms other than plants Nitrogen needed by cells for amino acids nucleic acids several other cell constituents Nucleotides have a nitrogen base so to make DNA and RNA or to replicate them they Obtained from food must have nitrogen Nitrogen fixing capable of using atmospheric nitrogen gas as a sole nitrogen source by converting it to ammonium nitrogenase is needed to do this Most prokaryotes obtain nitrogen from compounds such as ammonia and nitrate Acquisition of energy Phototrophs capture light energy to produce ATP Photosynthetic plants and many bacteria do this Chemotrophs capture energy from oxidation of reduced organic or inorganic compounds Humans are chemotrophs Electron sources organotrophs acquire their electrons from organic molecules ex glucose They need electrons to generate chemiosmosis and create ATP Lithotrophs rock eaters acquire their electrons from inorganic sources ex H2 gas elemental sulfur Do not need an organic substance energy sources Chemoorganotrophs energy from oxidation removing electrons of organic compounds Oxidizing means removing electrons from organic compounds These electrons are used to make ATP chemolithotrophs energy from oxidation of inorganic compounds Only in prokaryotes Advantage They may have a larger selection of nutrients because they have less competition Phototrophs contain pigments chlorophylls etc that allow them to use light as an energy source Advantage All they need is light Carbon sources Heteroptroph carbon source is organic carbon compounds Autotroph carbon source is carbon dioxide from the atmosphere to be used to These terms can be combined to more completely describe an organism make carbon containing molecules Example photoautotroph obtains energy from sunlight carbon from carbon dioxide Cyanobacteria are in this category Nutrient concentration Growth rate depends on the amounts of nutrients in the environment If nutrients are plentiful an organism will grow and reproduce faster too a degree Growth rate also depends on genetics One key nutrient available in the lowest amount will dictate how much growth can occur over time i e it will be a limiting factor when they run out of that nutrient they will stop growing This nutrient will determine how long and how quick an organism will grow Many times this limiting factor is a carbon source Effects of oxygen on microbial growth aerobes grow in the presence of oxygen They use oxygen for respiration Obligate aerobes REQUIRE atmospheric levels of oxygen atmospheric level 21 If it get below they they will not grow is quickly and if it geets too low they will not grow at all Microaerophiles grow best when there is less oxygen than normal 2 10 Always less than 21 Facultative aerobes anaerobes CAN use oxygen but can also grow in the absence of oxygen If oxygen is not present they will use something else as their final electron acceptor Effects of oxygen on microbial growth Anaerobic growth occurs without oxygen Aerotolerant aren t harmed by oxygen but don t use it either Oxygen is an inert gas to them Obligate anaerobes cannot grow when oxygen is present They will be killed if they are in the presence of oxygen Reducing agents thioglycolate can be added to nutrient broths to convert all O2 to water only top of culture is exposed to O2 in the air Anoxic anaerobe jars with a palladium catalyst convert O2 to water Factors affecting microbial growth Effects of oxygen on microbial growth Often determined by what defenses are available against oxygen s negative effects in the cell If organisms can deal with free radicals they can grow in the presence of oxygen If they cannot handle free radicals they cannot grow in the presence of oxygen and they will be killed If an organism is an aerobe it will produce one or more of the enzymes in the right column Effects of pH on microbial growth pH affects macromolecule structures and transmembrane electrochemical gradients If pH is too high or low it will affect ability to make ATP membranes and more Each microbe has an optimal pH range for growth acidophile pH 5 5 Saccharomyces cerevisiae Neutrophile pH 5 5 8 5 Get example Alkalophile basophile alkalinophiles pH 8 5 Get example Effects of osmotic pressure and water availability on microbial growth Used in food preservation Different solute concentrations can result in influx of water into or efflux from the cell This can cause stress to the cell causing it to either swell or shrink If the cell does not have a cell wall the cell may burst Most organisms grow best in an isotonic similar solute concentration inside and outside of the cell environment but some have adapted to grow best in hypertonic environments Halophiles like hypertonic environments salty places Osmophile organism that grows in high solute concentrations hypertonic environments Halophiles require salt for growth typically 1 4 Extreme halophiles require high levels 15 to 30 of salts for growth Halobacterium salinarum requires 25 salt lives in very salty lakes Halotolerant can survive at higher salt concentrations but grow best in the absence of salt Ex Staphylococcus aureus Staphylococcus epidermidis S aureus is a common cause of food poisoning because we use salt to preserve food and it can grow in salty environments Effects of temperature on microbial growth Temperature can also affect macromolecular structure cytoplasmic membrane fluidity and enzyme function We use temperature for our food Refrigeration freezing heating etc Different microbes have different optimal temperature growth ranges Psychrophiles 10 C 10 C Mesophiles 10 C 55 C Thermophiles 55 C 80 C