Elements Of Microbial Nutrition, Ecology, And Growth

Elements of Microbial Nutrition,Ecology, and Growth

Microbial Nutritionnutrition – process by which chemical substances(nutrients) are acquired from the environment andused for cellular activitiesessential nutrients - must be provided to anorganismTwo categories of essential nutrients:– macronutrients – required in large quantities; play principalroles in cell structure and metabolism proteins, carbohydrates– micronutrients or trace elements – required in smallamounts; involved in enzyme function and maintenance ofprotein structure manganese, zinc, nickel2

Nutrients Inorganic nutrients– atom or molecule that containsa combination of atoms other than carbon andhydrogen– metals and their salts (magnesium sulfate, ferric nitrate,sodium phosphate), gases (oxygen, carbon dioxide) andwater Organic nutrients- contain carbon and hydrogenatoms and are usually the products of living things– methane (CH4), carbohydrates, lipids, proteins, and nucleicacids3

Chemical Analysis of MicrobialCytoplasm 70% water Proteins 96% of cell is composed of 6 sphoroussulfurnitrogen4

Sources of Essential Nutrients Carbon sources Heterotroph – must obtain carbon in anorganic form such as proteins, carbohydrates,lipids and nucleic acids, made by other livingorganisms Autotroph - an organism that uses CO2, aninorganic gas as its carbon source– not nutritionally dependent on other living things5

Sources of Essential NutrientsNitrogen Sources Main reservoir is nitrogen gas (N2); 79% of earth’satmosphere is N2. Nitrogen is part of the structure of proteins, DNA, RNA& ATP – these are the primary source of N forheterotrophs. Somebacteria & algae use inorganic N nutrients (NO3 ,NO2 , or NH3). Some bacteria can fix N2. Regardless of how N enters the cell, it must beconverted to NH3, the only form that can be combinedwith carbon to synthesis amino acids, etc.6

Sources of Essential NutrientsOxygen Sources Major component of carbohydrates, lipids,nucleic acids, and proteins Plays an important role in structural andenzymatic functions of cell Component of inorganic salts (sulfates,phosphates, nitrates) and water O2 makes up 20% of atmosphere Essential to metabolism of many organisms7

Sources of Essential NutrientsHydrogen Sources Major element in all organic compounds andseveral inorganic ones (water, salts and gases) Gases are produced and used by microbes. Roles of hydrogen:– maintaining pH– forming H bonds between molecules– serving as the source of free energy in oxidationreduction reactions of respiration8

Sources of Essential NutrientsPhosphorous (Phosphate Sources) Main inorganic source is phosphate (PO4-3)derived from phosphoric acid (H3PO4) found inrocks and oceanic mineral deposits Key component of nucleic acids, essential togenetics Serves in energy transfers (ATP)9

Sources of Essential NutrientsSulfur Sources Widely distributed in environment, rocks;sediments contain sulfate, sulfides, hydrogensulfide gas and sulfur Essential component of some vitamins and theamino acids: methionine and cysteine Contributes to stability of proteins by formingdisulfide bonds10

Other Nutrients Important in MicrobialMetabolism Potassium – essential to protein synthesis andmembrane function Sodium – important to some types of cell transport Calcium – cell wall and endospore stabilizer Magnesium – component of chlorophyll;membrane and ribosome stabilizer Iron – component of proteins of cell respiration Zinc, copper, nickel, manganese, etc.11

Growth Factors: Essential OrganicNutrients Organic compounds that cannot be synthesizedby an organism because they lack the geneticand metabolic mechanisms to synthesize them Must be provided as a nutrient– essential amino acids, vitamins12

Nutritional Types Main determinants of nutritional type are:– carbon source – heterotroph, autotroph– energy source – chemotroph – gain energy from chemicalcompounds phototrophs – gain energy throughphotosynthesis13

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Transport: Movement of ChemicalsAcross the Cell Membrane Passive transport –does not require energy; substancesexist in a gradient and move from areas of higherconcentration towards areas of lower concentration– diffusion– osmosis – diffusion of water– facilitated diffusion – requires a carrier Active transport – requires energy and carrier proteins;gradient independent– active transport– group translocation – transported moleculechemically altered– bulk transport – endocytosis, exocytosis, pinocytosis15

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Environmental Factors ThatInfluence Microbes Environmental factors fundamentally affect thefunction of metabolic enzymes. Factors include:–––––temperatureoxygen requirementspHelectromagnetic radiationbarometric pressure21

3 Cardinal Temperatures Minimum temperature – lowest temperaturethat permits a microbe’s growth andmetabolism Maximum temperature – highest temperaturethat permits a microbe’s growth andmetabolism Optimum temperature – promotes the fastestrate of growth and metabolism22

3 Temperature Adaptation Groups1. Psychrophiles – optimum temperature below15oC; capable of growth at 0oC2. Mesophiles – optimum temperature 20o40oC; most human pathogens3. Thermophiles – optimum temperaturegreater than 45oC23

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Gas RequirementsOxygen As oxygen is utilized it is transformed intoseveral toxic products:– singlet oxygen (O2), superoxide ion (O2-), peroxide(H2O2), and hydroxyl radicals (OH-) Most cells have developed enzymes thatneutralize these chemicals:– superoxide dismutase, catalase If a microbe is not capable of dealing with toxicoxygen, it is forced to live in oxygen freehabitats.25

Categories of Oxygen Requirement Aerobe – utilizes oxygen and can detoxifyit Obligate aerobe - cannot grow withoutoxygen Facultative anaerobe – utilizes oxygenbut can also grow in its absence Microaerophilic – requires only a smallamount of oxygen26

Categories of Oxygen Requirement Anaerobe – does not utilize oxygen Obligate anaerobe - lacks the enzymes todetoxify oxygen so cannot survive in anoxygen environment Aerotolerant anaerobes – do no utilizeoxygen but can survive and grow in itspresence27

Carbon Dioxide RequirementAll microbes require some carbon dioxide intheir metabolism. Capnophile – grows best at higher CO2tensions than normally present in theatmosphere28

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Effects of pH Majority of microorganisms grow at a pHbetween 6 and 8 Obligate acidophiles – grow at extremeacid pH Alkalinophiles – grow at extreme alkalinepH30

Osmotic Pressure Most microbes exist under hypotonic orisotonic conditions Halophiles – require a high concentrationof salt Osmotolerant – do not require highconcentration of solute but can tolerate itwhen it occurs31

Other Environmental Factors Barophiles – can survive under extremepressure and will rupture if exposed tonormal atmospheric pressure32

Ecological Associations AmongMicroorganisms Symbiotic – organisms live in close nutritionalrelationships; required by one or both members– mutualism – obligatory, dependent; both membersbenefit– commensalism – commensal member benefits,other member not harmed– parasitism – parasite is dependent and benefits;host is harmed33

Ecological Associations AmongMicroorganisms Non-symbiotic – organisms are free-living;relationships not required for survival– synergism – members cooperate and sharenutrients– antagonism – some member are inhibited ordestroyed by others34

Interrelationships BetweenMicrobes and Humans Human body is a rich habitat for symbioticbacteria, fungi, and a few protozoa normal microbial flora Commensal, parasitic, and synergistic35

Microbial Biofilms Biofilms result when organisms attach toa substrate by some form of extracellularmatrix that binds them together in complexorganized layers Dominate the structure of most naturalenvironments on earth Communicate and cooperate in theformation and function of biofilms –quorum sensing36

The Study of Microbial Growth Microbial growth occurs at two levels:growth at a cellular level with increase insize, and increase in population Division of bacterial cells occurs mainlythrough binary fission (transverse)– parent cell enlarges, duplicates itschromosome, and forms a central transverseseptum dividing the cell into two daughtercells37

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Rate of Population Growth Time required for a complete fission cycle iscalled the generation, or doubling time Each new fission cycle increases thepopulation by a factor of 2 – exponential orlogarithmic growth. Generation times vary from minutes todays.39

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Rate of Population Growth Equation for calculating population sizeover time:nNƒ (Ni)2Nƒ is total number of cells in the population.Ni is starting number of cells.Exponent n denotes generation time.n2 number of cells in that generation41

The Population Growth Curve 1.2.3.4.In laboratory studies, populations typically display apredictable pattern over time – growth curve.Stages in the normal growth curve:Lag phase – “flat” period of adjustment, enlargement;little growthExponential growth phase – a period of maximumgrowth will continue as long as cells have adequatenutrients and a favorable environmentStationary phase – rate of cell growth equals rate of celldeath caused by depleted nutrients and O2, excretion oforganic acids and pollutantsDeath phase – as limiting factors intensify, cells dieexponentially in their own wastes42

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Methods of Analyzing PopulationGrowth Turbidometry – most simple Degree of cloudiness, turbidity, reflects therelative population size Enumeration of bacteria:– viable colony count– direct cell count – count all cells present;automated or manual44

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Elements of Microbial Nutrition, Ecology, and Growth. 2 Microbial Nutrition nutrition –process by which chemical substances (nutrients) are acquired from the environment and used for cellular activities essential nutrients - must be provided to an organism Two categories of essential nutrients: