The flagellar motor is reversible CCW: runCW: tumble.
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The flagellar motor is reversible CCW: runCW: tumble
E. coli responds to chemical gradients by biasing its random walk No stimulus Gradient of chemoattractant [Asp], e.g.
Chemotaxis - the ability to sense and respond to extracellular concentration gradients of solutes Chemoreceptors Input Output: motor bias, CCW CW rotation CheY – P - CW signal - 3 sec. lag bacterial cell
There are likely four different types of surface motility systems (each may be genetically unique) 1) Twitching - extension and retraction of a pilus (type IV) - found in multiple groups of bacteria 2) Cyanobacteria - polysaccharide extrusion 3) Mycoplasma - ATP driven system of just two proteins 4) Flavobacteria - Unknown
What is Known about Flavobacterial Motility - the cell surface is smooth and featureless by EM - motility is connected to the ability to utilize the insoluble polysaccharide chitin - non-motile cells are resistant to bacteriophage - a number of the genes essential to motility have homologs involved in macromolecular transport
OM PG CM Direction of Cell Movement H+H+ H+?H+? ATP? Substratum Macromolecule Transport Model of F. johnsoniae Gliding
Summary There are two classes of bacterial motility - flagellar (swimming) - bacterial vs. archaeal flagella - horizontal gene transfer - chemotaxis - surface motility - twitching (type IV pili) - polysaccharide secretion - ATP driven - Flavobacterial system - may involve transport
Chapter 5: Nutrition, Cultivation, and Isolation of Microbes Evolution of Metabolic Diversity Bacterial Nutrition Types 1-2-1, C-H-O ratio, Most biosynthesis is done using units of CH 2 O. So if an organism is using sunlight for energy and CO 2 as a carbon source then it needs a source of H+ (in plants it would be H 2 O ). Carbon Source: CO 2 or other organic carbon Energy Source: Sunlight or chemical energy Alternate Terminal Electron Acceptors (other than O 2 ) CO, NO 3, SO 4, SO 3, oxidized metals
Bacterial Nutrition Types: Photoautotroph Carbon source: CO 2 Energy source: Sunlight * Photoheterotroph Carbon source: Carbon compounds Energy source: Sunlight * Chemoautotroph Carbon source: CO 2 Energy source: chemical energy (H 2 S, H 2, metals, etc.) Chemoheterotroph Carbon source: Carbon compounds Energy source: Reduced carbon compounds (CH 2 O)
Some Terms (as applicable to microbial growth) Aerobic vs. Anaerobic Obligate: required for survival Facultative: optimal for growth but not required for survival Trace (Micro Nutrient): required in very small amounts Sole Source: the cited molecule can satisfy an organism’s needs for a particular nutritional requirement alone, with no need for additional sources (often seen in selective growth media) Enrichment Culture: A technique to encourage the growth of a specific microbe using metabolic traits particular to that organism from a starting mixture of many organisms. (ex. Mycobacterium)
Getting Nutrients into the Cell --- remember the cytoplasmic membrane is a true permeability barrier, most nutrients can’t cross on their own Diffusion: Use existing concentration gradients to move material in or out of the cell. Usually requires a channel protein (facilitated diffusion) Group Transport: A sort of one-way facilitated diffusion, utilizes an existing concentration gradient to get molecules into the cell and then chemically modifies the molecule to prevent its escape back out through the channel protein in the membrane Active Transport: Use an energy source to offset the “cost” of moving a molecule against its concentration gradient
Uptake of Micronutrients Siderophores: small organic molecules able to bind specific substrates with very high affinity --- used to capture low abundance micronutrients from the cell’s surrounding environment --- usually coupled with a specific uptake system of proteins on the cell’s surface Enterobactin, from E. coli