Micro303Lecture13 - Microbiology 303 Fall 2012 Lecture 13 Microbial Growth What is growth For microbes growth is an increase in mass over?me Most [email protected]

Micro303Lecture13 - Microbiology 303 Fall 2012 Lecture 13...

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Unformatted text preview: Microbiology 303 Fall 2012 Lecture 13 Microbial Growth What is growth? For microbes: growth is an increase in mass over ?me Most [email protected] an increase in numbers Binary fission and its consequences STEPS IN BINARY FISSION Increase in cell length Increase in cell volume Cell wall biosynthesis DNA replica?on Chromosome segrega?on Septum forma?on Cell wall synthesis at division site Cell separa?on Cell division and the cytoskeleton Chromosome separa?on FtsZ ring forms at center Not MreB The divisome How does FtsZ find the middle? The Min system MinE movement promotes MinCD dissassembly MinCD assembles at pole Where is the least Min? Thanbichler and Shapiro 2008 Nat Rev Microbiol. 6: 28 ­40. MinE finds MinCD boundary Cell wall growth pa[erns Note asymmetry: cells are polar Cabeen, Jacobs ­Wagner J. Cell Biol. 2008:179:381 ­387 Caulobacter cell cycle Swarmer cell Stalk cell Ac?nomycetes: filamentous growth Streptomyces growth cycle Fungal growth pa[erns Bdellovibrio: mul?ple fission Measuring growth? Measure cell number Measure feature associated with cell •  Turbidity (light sca[ering) •  Weight •  Total cell counts (plated) •  Cfu = colony forming unit •  Viable cell counts •  Protein Measuring turbidity Growth of a popula?on: batch culture •  One cell becomes two = genera?on •  Time this takes = genera<on <me, or doubling <me •  Growth rate measures the number of genera?ons per ?me in log phase Growth rate •  Varies tremendously –  Vibrio cholerae – 10 minutes –  Mycobacterium spp. – 24 hours •  Gene?c factors –  Rate of enzyme catalysis –  Speed of chromosome replica?on and cell division –  Metabolic rate •  Environmental factors –  Nutrient availability –  Environmental factors Adapta?on to environmental changes •  Oxida?ve stress –  Detoxifica?on enzymes –  Damage repair systems for DNA •  Water stress –  Transport proteins and compa?ble solutes •  Temperature change –  Cold Shock response –  Heat Shock response •  pH change –  Acid challenge and acid tolerance EB = elementary body RB = re?culate body Are there limits to growth? How does the cell respond? •  Nutrient storage (inclusions) –  Carbon storage •  Glycogen, polyhydroxyalkanoates –  Energy source storage •  Sulfur globules, polyphosphate •  Sta?onary phase and starva?on survival –  Metabolic changes –  Developmental processes Myxobacteria respond to nutrient depriva?on Dictyostelium lifecycle Some cells form cysts: Giardia GI tract Escape to environment GI tract Ankarklev et al. Nature Reviews Microbiology 8, 413-422 (June 2010) Endospore forma?on is a response to nutrient depriva?on The most resistant microbial form III How do we control growth? Steriliza<on  ­ kills all viable organisms, including endospores Disinfec?on  ­ removal of pathogens from inanimate surfaces, may not eliminate all microbes An?sepsis  ­ removal of pathogens from living ?ssue, may not eliminate all microbes Sanita?on  ­ removal of pathogens to safe level Physical methods for control Heat Heat plus pressure = autoclave Pasteuriza?on: heat and ?me sufficient to kill pathogens 63 ˚C for 30 min 72 ˚C for 15 sec Cold refrigera?on doesn’t usually kill microbes freezing might if sufficient ice crystals formed; cryoprotectants are used in the lab to maintain cultures in the freezer Chemical methods for control Phenolics, alcohols, aldehydes, detergents, gases, heavy metals, oxidizing agents, etc Generally target DNA or proteins, as solvents, alkyla?ng agents, oxidizing agents, or denaturants Effec?veness is affected by presence of organic ma[er, kind of microbe, ?me, concentra?on, biofilms, etc Are general purpose = biocides affect many cellular processes affect many life forms Chemicals for growth control For illustra?on only Biological control of growth: an?microbials Antifungals (Antibiotics) Antibacterial For illustra?on only Antiviral An?bio?cs have selec<ve toxicity An?bio?cs target a specific cellular process Do not need to know an?bio?cs in each class, except those discussed further An?bio?cs that affect metabolism Microbial an?bio?c resistance [email protected] fitness costs •  Decrease permeability –  Changes to membrane lipids, cell wall, OM, porins, etc •  Pump out an?bio?c –  Efflux pumps •  Alter target –  e.g. ribosome modifica?ons •  Inac?vate an?bio?c –  Modify or degrade •  Produce alterna?ve target Pagès, James & Winterhalter Nature Reviews Microbiology 6, 893-903 (December 2008) An?bio?c resistance: degrada?on of the an?bio?c β-lactamase Narrow spectrum versus broad spectrum or even extended spectrum An?bio?c resistance: target subs?tu?on •  PBP2 is target for β ­lactams •  S. aureus mecA gene encodes MecA protein, also called PBP2’ •  PBP2’ s?ll can perform transpep?dase reac?on, but does not bind to β ­lactam drugs •  S. aureus with mecA is MRSA (methicillin resistant) An?bio?c resistance: target subs?tu?on Hughes Nature Reviews Genetics 4, 432-441 (June 2003) ...
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