MMG301 1nd Edition Lecture 18Outline of Last Lecture I. Growth batch culturesOutline of Current Lecture II. Stationary phase survivalIII. Bacterial cell-to-cell communication (quorum sensing)IV. Microbial biofilmsCurrent Lecture-stationary phase starvation survival: long starvation periods alternate with transient growth periods-starvation survival: 3-4 generations per year-adaptation to starvation and other stresses-starvation strategies for bacteria-1. bacterial differentiation into endospores -only a few bacterial genera-2. bacterial adaptation without cell differentiation: physiological changes without highlydifferentiated cells-used by most bacteria-starvation strategies used by non-differentiating bacteria-1. turnover of cell macromolecules to produce metabolic energy-degrade storage polymers-autodegradation of cellular constituents (highly controlled process), degrade only things that are no longer needed-2. stringent control of macromolecular synthesis:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-guanosine tetraphosphate (ppGpp) and pentaphosphate (pppGpp)…signal molecules called alarmones (produced by RelA), alert the cell that something is wrong-global control effect: -down-regulate synthesis of macromolecules required for fast growth; down-regulate what is not needed-up-regulate Stationary Phase Inducible (SPI) proteins; up-regulate what isneeded-(1) “eat what you don’t need”; (2) “make only what you need”-3. new nutrient transport systems with enhanced uptake efficiency-high-affinity transport systems (e.g., Fe-chelator system for iron)-broad substrate specificity “Beggars can’t be choosy” -4. protective changes in bacterial cell architecture-increased encapsulation-transient increase in flagella (helping them relocate to area with more nutrients)and fimbriae (helping them attach to new environment)-decreased cell size increases cell surface/volume ratio-nucleoid proteins to protect DNA, more histone like proteins, DNA gyrase and topoisomerase-more peptidoglycan layers and cross-linking to protect against increased stress, cell is more likely to retain its shape despite unfavorable conditions-gram-negative bacteria: more LPS and fewer outer membrane proteins-cell to cell communication-Quorum Sensing (QS): population density monitored by autoinducers. always produced-autoinducer diffuses in/out of the cell-concentration in = concentration out-when the autoinducer concentration increases to a threshold value, this triggers a bacterial response in quorum settings-Gram- : acyl homoserine lactone -Gram+ : small peptide-cross-species signals-multiple controls of the same pathway: sporulation and DNA uptake-quorum sensing signals controlling mutually exclusive lifestyles-microbial biofilms-growth on surfaces (higher nutrients concentrations, protection)-continuous cell density = biofilms-cells immobilized in an polymer matrix of microbial
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