Lecture Set 3 : Part 5 Flashcards
what are the effects of pH on microbial growth?
-the pH of an environment will greatly affect microbial growth
-most organisms in our lab grow best between a pH of 5.5 and 8
-some organisms have evolved to grow best at a low or high pH
what do we call the organisms that grow best at a pH between 5.5 and 9?
-neutrophiles
what do we call organisms that grow best at a pH of 5.5 or lower?
-acidophiles
-relatively common
what do we call organisms that grow best at a pH of 8 or higher?
-alkaliphiles
-less common because there are few naturally basic environments
what do acidophiles have?
-cytoplasmic membranes that require high external H+ concentrations for stability
what problem do alkaliphiles have?
-have a problem with maintaining a H+ gradient when the environment is rich in OH- ions
-the H+ ions that are pumped out of the cell immediately react with OH- to form water, so the cell cannot use them to generate energy
how do alkaliphiles solve their problem?
-place a reliance on a sodium motive force (Na+ gradient)
-works in place of H+ because Na+ is another positive ion with a +1 charge
what are the aspects of the cytoplasmic membrane that remain the same despite the different pH preferences of organisms?
-cytoplasmic pH is maintained near neutrality
-has very low permeability to H+ and OH-
what is the importance of buffers in media?
-help to maintain a constant pH
-each organism has its own optimal pH for growth
-some bacteria can produce acids that decrease pH
-some bacteria release ammonia which increases pH
what are acids that bacteria can release causing pH to decrease? how does bacteria produce these acids?
-acetic acid
-lactic acid
-sulfuric acid
-produced by fermentation (sugars are converted into acid end products)
what bacteria release ammonia?
-urease producing bacteria
-break urea into NH3 and CO2
what are non-halophiles?
-bacteria that grow best at low salt concentrations
-less than 1% NaCl (best growing conditions)
-cytoplasm has a higher solute concentration than surroundings (water will move in)
-water moving in produces turgor pressure
what are halotolerant bacteria?
-bacteria that can tolerate some reduction in water activity of the environment but still grow best at lower salt concentrations
what is an example of a halotolerant bacteria?
-staphylococcus aureus
-lives on human skin
-can tolerate up to 17.5% NaCl (doesnt grow at this concentration)
-is an opportunistic pathogen
what are halophiles?
-grow best at reduced water potential
-have a very specific requirement for NaCl
-many marine microbes
what are extreme halophiles?
-requires high levels of NaCl for growth (15%-30%)
-ex: microbes from great salt lake or the dead sea
how do cells typically combat high environmental solute concentrations?
-by accumulating compatible solutes in the cytoplasm
-done with solutes that dont interfere with metabolism
-results in a net inflow of water (for turgor pressure)
what are the most common compatible solutes?
-amino acids (proline, glutamate) = most bacteria
-sugars (sucrose, trehalose) = cyanobacteria
-alcohols (glycerol, mannitol) = eukaryotes
-salts (KCl) = extremely halophilic archaea
what are obligate aerobes?
-require oxygen for metabolism (aerobic respiration)
what are strict anaerobes?
-do not require oxygen and may even be killed by it
what are facultative anaerobes?
-can live with or without oxygen
-will use it for respiration when it is available as it is more efficient
what are aerotolerant anaerobes?
-can tolerate oxygen and grow in its presence but dont use it for anything
what are microaerophiles?
-require oxygen in small amounts
-cannot tolerate regular atmosphere levels of oxygen
what is the thiogylcolate broth experiment used for?
-used to demonstrate oxygen response by different bacteria
