Chapter 7 Microbial Growth Binary fission Steps in Binary Fission ...

Chapter 7Topics–Microbial Growth–Factors that affect microbialgrowth–Microbial NutritionMicrobial Growth• Binary fission• Generation time• Growth curve• Enumeration of bacteriaDefinition of growth- Unicellular organisms increase in size toapproximately two times the original size- At that time the mother cell divides into twodaughter cells by binary fission- The daughter cells grow - become mothercells and divideWith each division, the population doublesBinary fission• The division of a bacterial cell• Parental cell enlarges and duplicatesits DNA• Septum formation divides the cellinto two separate chambers• Complete division results in twoidentical cellsSteps in Binary FissionShouldbe pink –RIGHT??Generation time• The time required for a completedivision cycle (doubling)• Length of the generation time is ameasure of the growth rate• Exponentials are used to define thenumbers of bacteria after growth1

LogSynchronous growth vs.nonsynchronous growthGrowth curve• Lag phase• Log phase• Stationary phase• Death phase2

Enumeration of bacteria• Direct cell count - multiple methods• Turbidity• Automated devices– Coulter counter– Flow cytometerDifferences in techniques - can you tellthe difference between live/dead?One bacterium results inone bacterial colonyCountable number of coloniesLimitation = 30 to 300 per plateTurbidityDirect counts by microscopy - can takeadvantage of staining techniques welearned in Chapter 33

Mechanical or automated countersFactors that Effect MicrobialGrowth• Temperature• Gas• pH• Osmotic pressure• Other factors• Microbial associationTemperature-Psychrophiles obligate (Bacillus globisporus),facultative (Xanthomonas pharmicola) – optimaltemperature for growth below 15°C- Mesophiles - 20 to 40 o C - thermoduricorganisms can survive elevated temperatures,but grow best at moderate temperatures- Thermophiles – organisms that normally growbest at >45°CGases• Two gases that most influencemicrobial growth– Oxygen• Respiration• Oxidizing agent– Carbon dioxideOxygen -- Obligate aerobes- Obligate anaerobes- Facultative anaerobes- Microaerophiles - do not grow at normalatmospheric concentrations of O 2 - soilmicroorgansims- Capnophiles - microaerophiles that areCO 2loving4

Obligate aerobe• Requires oxygen for metabolism• Possess enzymes that can neutralizethe toxic oxygen metabolites– Superoxide dismutase andcatalase• Ex. Most fungi, protozoa, andbacteriaFacultative anaerobe• Does not require oxygen formetabolism, but can grow in its presence• During oxygen limitation states, anaerobicrespiration or fermentation occurs• Possess superoxide dismutase andcatalase• Ex. Gram negative pathogensObligate anaerobes• Cannot use oxygen for metabolism• Do not possess superoxide dismutaseand catalase• The presence of oxygen is toxic to thecell• Ex - dental pathogens, intestinalpathogens, deep in tissuespHpH - negative logarithm of thehydrogen ion concentration of anaqueous solution• Most cells grow best between pH 6 - 8• Exceptions would be acidophiles (pH 0)and alkalinophiles (pH 10).Osmotic pressure• Halophiles• Require high salt concentrations• Withstand hypertonic conditions• Ex. Halobacterium• Facultative halophiles– Can survive high salt conditions but isnot required– Ex. Staphylococcus aureusOther factors?• Barophiles – withstand highpressures• Spores and cysts- can survive dryhabitats5

Hydrostatic pressureMost microorganisms can withstandreasonable pressures, but barophilesare highly evolved microorganisms thatgrow only at intense pressureSome barophiles are also thermophiles- deep thermal vents in oceansEcological association• Influence microorganisms have on othermicrobes– Symbiotic relationship– Non-symbiotic relationship• Organisms that live in close nutritionalrelationship• Types– Mutualism – both organism benefit– Commensalism – one organisms benefits– Parasitism – host/microbe relationshipEcology of CommunitiesClint Eastwood StyleGood – help each other in communitysettingBad – kill one another with antibiotics –take spoils of victoryUgly – live together to cause diseaseOral cavity biofilms and Co-aggregationTwo SpeciesBiofilmFormed by:S. oralis &P. acnes6

Microbial Nutrition• Sources of essential nutrients- Macronutrients: Carbon, Nitrogen, Oxygen,and Hydrogen- Micronutrients: Magnesium, Manganese,Zinc, and Nickel• Transport mechanismsCarbon source• Heterotroph (depends on other life forms)– Organic molecules– Ex. Sugars, proteins, lipids• Autotroph (self-feeders)– Inorganic molecules– Ex. CO 2Transport mechanisms• Osmosis• Diffusion• Active transport• Endocytosis- Water movement- Selectively permeablemembrane- Concentration gradientOsmosis – water movementEqual In Burst Out ShrinkDiffusion• Net movement of molecules from a highconcentrated area to a low concentratedarea• No energy is expended (passive)• Concentration gradient and permeabilityaffect movement7

Sugar diffusion in coffeeFacilitated diffusion• Transport of polar molecules and ionsacross the membrane• No energy is expended (passive)• Carrier protein facilitates the bindingand transport– Specificity– Saturation– CompetitionFacilitated diffusionActive transport• Transport of molecules against agradient• Requires energy (active)• Ex. Permeases and protein pumpstransport sugars, amino acids, organicacids, phosphates and metal ions• Ex. Group translocation transports andmodifies specific sugarsPermeases Group translocation -usually entities are modified8

Endocytosis• Substances are taken, but are nottransported through the membrane.• Requires energy (active)• Common for eukaryotes• Ex. Phagocytosis, pinocytosisIn summaryThe growth and division ofmicroorganisms requires a carefullychoreographed arrangement of alarge number of processes. Littlethings can be exceedingly complex.9