8_30 growth II.pptx

Bacterial Growth II. Why should you care? Treatment implications Urgency of care Ability to control  Bacterial Growth in Laboratory Conditions Cells in laboratory grown in closed or batch system – No new input of nutrients and no release of wastes Population of cel...

Bacterial Growth II. Why should you care? Treatment implications Urgency of care Ability to control  Bacterial Growth in Laboratory Conditions Cells in laboratory grown in closed or batch system – No new input of nutrients and no release of wastes Population of cells increase in predictable fashion – Follows a pattern called growth curve  Bacterial Growth in Laboratory Conditions The Growth Curve – Characterized by five distinct stages Lag stage Exponential or log stage Stationary stage Death stage Phase of prolonged decline  Bacterial Growth in Laboratory Conditions Lag phase – Number of cells does not increase – Cells prepare for growth “tooling up” Log phase – Period of exponential growth Doubling of population with each generation – Produce primary metabolites Compounds required for growth – Cells enter late log phase Synthesize secondary metabolites – Used to enhance survival – antibiotics  Bacterial Growth in Laboratory Conditions Stationary phase – Overall population remains relatively stable Cells exhausted nutrients Cell growth = cell death – Dying cell supply metabolites for replicating cells Death phase – Total number of viable cells decreases Decrease at constant rate – Death is exponential Much slower rate than growth  Bacterial Growth in Laboratory Conditions Phase of prolonged decline – Once nearly 99% of all cells dead, remaining cells enter prolonged decline – Marked by very gradual decrease in viable population – Phase may last months or years – Most fit cells survive Each new cell more fit than previous  Possible reasons for entry into stationary phase nutrient limitation limited oxygen availability toxic waste accumulation critical population density reached Starvation responses morphological changes – e.g., endospore formation decrease in size, protoplast shrinkage, and nucleoid condensation production of starvation proteins Accumulation of mutations long-term survival increased virulence  Death Phase Few survivors best adapted two alternative hypotheses – Cells are Viable But Not Culturable (VBNC) Cells alive, but dormant – programmed cell death Fraction of the population genetically programmed to die (commit suicide)  Loss of Viability Figure 6.8  Prolonged Decline in Growth bacterial population continually evolves Increased mutation rate process marked by successive waves of genetically distinct varients natural selection occurs Figure 6.9  Growth in Nature Planktonic growth: growth as suspension Sessile growth: attached to surface can develop into biofilms attached polysaccharide matrix containing embedded bacteria (Figure 5.4a) Biofilms form in stages: Planktonic cells attach. Sticky matrix forms. Quorum sensing Microbial mats: multilayered sheets with different organisms in each layer  Biofilms Biofilms prevent harmful chemicals (e.g., antibiotics) from penetrating, prevent protists from grazing, and prevent washing away of cells. Biofilms affect human health, water distribution systems, and fuel storage.  Environmental Factors on Growth As group, prokaryotes inhabit nearly all environments – Some live in “comfortable” habitats – Some live in harsh environments Most of these are termed extremophiles and belong to domain Archaea Major conditions that influence growth – Temperature – Oxygen – pH – Water availability  Environmental Factors on Growth Psychrophile Temperature – Optimum temperature -5°C to – Each species has well 15°C Found in Arctic and Antarctic defined temperature range regions Within range lies optimum Psychrotroph – 20°C to 30°C growth temperature Important in food spoilage – Prokaryotes divided into 5 Mesophile categories – 25°C to 45°C More common Disease causing Thermophiles – 45°C to 70°C Common in hot springs Hyperthermophiles – 70°C to 110°C Usually members of Archaea Found in hydrothermal vents Figure 6.2 Figure 6.3  Environmental Factors on Growth Oxygen – Prokaryotes divided based on oxygen requirements Obligate aerobes – Absolute requirement for oxygen » Use for energy production Obligate anaerobes – No multiplication in presence of oxygen » May cause death Facultative anaerobes – Grow better with oxygen » Use fermentation in absence of oxygen Microaerophiles – Require oxygen in lower concentrations » Higher concentration inhibitory Aerotolerant anaerobes – Indifferent to oxygen, grow with or without » Do not use oxygen to produce energy 5.14 Oxygen and Microbial Growth Why is oxygen toxic? Molecular oxygen (O2) is not toxic. Exposure to oxygen yields toxic byproducts. (Figure 5.27) superoxide anion (O2-) hydrogen peroxide (H2O2) hydroxyl radical (OH·) Figure 5.25 SOD = superoxide dismutase  Environmental Factors on Growth pH – Bacteria survive within pH range – Neutrophiles Multiply between pH of 5 to 8 – Maintain optimum near neutral – Acidophiles Thrive at pH below 5.5 – Maintains neutral internal pH, pumping out protons (H+) – Alkalophiles Grow at pH above 8.5 – Maintain neutral internal pH through sodium ion exchange » Exchange sodium ion for external protons  Environmental Factors on Growth Water availability – All microorganisms require water for growth – Water not available in all environments In high salt environments – Bacteria increase internal solute concentration » Synthesize small organic molecules – Osmotolerant bacteria tolerate high salt environments – Bacteria that require high salt for cell growth termed halophiles Figure 6.4 - Overview  Nutritional Factors on Growth Growth of prokaryotes depends on nutritional factors as well as physical environment Main factors to be considered are: – Required elements – Growth factors – Energy sources – Nutritional diversity  Nutritional Factors on Growth Required elements – Major elements Carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, magnesium, calcium and iron – Essential components for macromolecules – Organisms classified based on carbon usage Heterotrophs – Use organism carbon as nutrient source Autotrophs – Use inorganic carbon (CO2) as carbon source – Trace elements Cobalt, zinc, copper, molybdenum and manganese – Required in minute amounts  Nutritional Factors on Growth Growth factors – Some bacteria cannot synthesize various cell constituents These must be added to growth environment – Referred to as growth factors – Organisms can display wide variety of Growth factor requirements Some need very few while others require many – These termed fastidious = fussy  Nutritional Factors on Growth Energy Sources – Organisms derive energy from sunlight or chemical compounds Phototrophs – Derive energy from sunlight Chemotrophs – Derive energy from chemical compounds – Organisms often grouped according to energy source  Nutritional Factors on Growth Nutritional Diversity – Organisms thrive due to their ability to use diverse sources of carbon and energy – Photoautotrophs Use sunlight and atmospheric carbon (CO2) as carbon source – Called primary producers (Plants) – Chemolithoautotrophs a.k.a chemoautotrophs or chemolitotrophs Use inorganic carbon for energy and use CO2 as carbon source – Photoheterotrophs Energy from sunlight, carbon from organic compounds – Chemoorganoheterotrophs a.k.a chemoheterotrophs or chemoorganotrophs Use organic compounds for energy and carbon source Most common among humans and other animals  Laboratory Cultivation Knowing environmental and nutritional factors makes it possible to cultivate organisms in the laboratory Organisms are grown on culture media – Media is classified as complex media or chemically defined media  Laboratory Cultivation Complex media – Contains a variety of ingredients – There is no exact chemical formula for ingredients Can be highly variable – Examples include Nutrient broth Blood agar Chocolate agar Table 6.4  Laboratory Cultivation Chemically defined media – Composed of precise amounts of pure chemical – Generally not practical for routine laboratory use Invaluable in research – Each batch is chemically identical » Does not introduce experimental variable Table 6.2  Laboratory Cultivation Selective media – Inhibit the growth of unwanted organisms Allow only sought after organisms to grow – Example Thayer-Martin agar – For isolation of Neisseria gonorrhoeae MacConkey agar – For isolation of Gram negative bacteria  Laboratory Cultivation Differential media – Contains substance that bacteria change in recognizable way – Example Blood agar – Certain bacteria produce hemolysin to break down RBC » Hemolysis MacConkey agar – Contains pH indicator to identify bacteria that produce acid  Next time More growth Detecting Bacterial Growth