Chapter 7Chapter 7

ELEMENTS OF MICROBIAL ELEMENTS OF MICROBIAL NUTRITION, ECOLOGY, & NUTRITION, ECOLOGY, &

GROWTHGROWTH

Microbial Nutrition, Ecology & Microbial Nutrition, Ecology & Growth Growth

Sources of Nutrition - Nutrition consists of taking in chemical Sources of Nutrition - Nutrition consists of taking in chemical substances (nutrients) and assimilating and extracting substances (nutrients) and assimilating and extracting energy from them energy from them Essential nutrients – substances required for survival; Essential nutrients – substances required for survival;

can be macronutrients or micronutrientscan be macronutrients or micronutrients Macronutrients are required in relatively large Macronutrients are required in relatively large

quantities and play principal roles in cell structure and quantities and play principal roles in cell structure and metabolismmetabolism

Carbon - supplied in media as either Carbon - supplied in media as either carbohydrates (sugars) and/or peptonescarbohydrates (sugars) and/or peptones

Nitrogen, sulfur, and phosphorus - needed for Nitrogen, sulfur, and phosphorus - needed for proteins & nucleic acids; supplied as peptonesproteins & nucleic acids; supplied as peptones

Micronutrients, or trace elements are present in Micronutrients, or trace elements are present in smaller amounts and are involved in enzyme function smaller amounts and are involved in enzyme function and maintenance of protein structureand maintenance of protein structure

Trace elements (Fe, Cu, Mg, and Zn) - needed for Trace elements (Fe, Cu, Mg, and Zn) - needed for coenzymes; usually present in watercoenzymes; usually present in water

Microbial Nutrition, Ecology & Microbial Nutrition, Ecology & GrowthGrowth

Organic nutrients contain carbon and hydrogen Organic nutrients contain carbon and hydrogen atoms and are usually the products of living atoms and are usually the products of living thingsthings

Organic growth factors - needed by fastidious Organic growth factors - needed by fastidious (have special growth requirements) organisms(have special growth requirements) organisms

Essential compounds not synthesized by Essential compounds not synthesized by organismsorganisms

Supplied in media in purified form or as body Supplied in media in purified form or as body fluids (e.g. blood, serum, etc.)fluids (e.g. blood, serum, etc.)

Examples: vitamins, amino acids, purines, Examples: vitamins, amino acids, purines, pyrimidines, hemin, NAD, etc.pyrimidines, hemin, NAD, etc.

Inorganic nutrients are atoms or simple Inorganic nutrients are atoms or simple molecules that contains a combination of atoms molecules that contains a combination of atoms other than carbon and hydrogenother than carbon and hydrogen

Nutritional Categories Nutritional Categories An autotroph depends on An autotroph depends on

carbon dioxide for its carbon carbon dioxide for its carbon needsneeds If its energy needs are met If its energy needs are met

by light, it is a by light, it is a photoautotroph, but if it photoautotroph, but if it extracts energy from extracts energy from inorganic substances, such inorganic substances, such as soil and minerals, it is a as soil and minerals, it is a chemoautotrophchemoautotroph

A heterotroph acquires carbon A heterotroph acquires carbon from organic moleculesfrom organic molecules A saprobe is a decomposer A saprobe is a decomposer

that feeds upon dead that feeds upon dead organic matterorganic matter

A parasite feeds from a live A parasite feeds from a live host and usually causes host and usually causes harmharm

Disease-causing parasites Disease-causing parasites are pathogensare pathogens

SaprobesSaprobes

Requirements for Growth Requirements for Growth Environmental factors - can be used in selective isolationEnvironmental factors - can be used in selective isolation

Temperature - range and optimum different for each species; Temperature - range and optimum different for each species; related to protein (enzyme) stabilityrelated to protein (enzyme) stability

Psychrophile (cold loving) - 5 C - 30 CPsychrophile (cold loving) - 5 C - 30 C Mesophile - 10 - 45 CMesophile - 10 - 45 C Thermophile - 25 - 95 CThermophile - 25 - 95 C

Requirements for GrowthRequirements for Growth

pH - range and optimum differ with organism; pH - range and optimum differ with organism; most = 6.5-7.5; buffers used in media to most = 6.5-7.5; buffers used in media to maintain pH in proper rangemaintain pH in proper range

Acidophiles prefer lower pHAcidophiles prefer lower pH Alkalinophiles prefer higher pHAlkalinophiles prefer higher pH

Osmotic pressure (solute concentration) - Osmotic pressure (solute concentration) - maintains water conc.; most cells require maintains water conc.; most cells require isotonic (0.9%) solutions; some can tolerate isotonic (0.9%) solutions; some can tolerate hypertonic (halophiles - e.g. vibrios & hypertonic (halophiles - e.g. vibrios & staphylococci) and hypotonic solutions; used as staphylococci) and hypotonic solutions; used as preservativespreservatives

Requirements for GrowthRequirements for Growth Oxygen - requirements based on presence of catalase, Oxygen - requirements based on presence of catalase,

peroxidase and superoxide dismutase (enzymes that peroxidase and superoxide dismutase (enzymes that handle toxic by-products)handle toxic by-products) Source = atmosphere or chemical (organic or Source = atmosphere or chemical (organic or

inorganic)inorganic) Classification based on oxygen requirementClassification based on oxygen requirement

Strict (obligate) aerobes - use molecular oxygen; Strict (obligate) aerobes - use molecular oxygen; have catalase and dismutase - e.g. have catalase and dismutase - e.g. PseudomonasPseudomonas

Strict (obligate) anaerobes - free oxygen is toxic; Strict (obligate) anaerobes - free oxygen is toxic; use inorganic oxygen-containing salts; generally use inorganic oxygen-containing salts; generally lack both catalase and dismutase - e.g. lack both catalase and dismutase - e.g. ClostridiumClostridium

Facultative anaerobes - prefer molecular oxygen but Facultative anaerobes - prefer molecular oxygen but can grow without it; have catalase and dismutase - can grow without it; have catalase and dismutase - e.g. e.g. EscherichiaEscherichia

Aerotolerant anaerobe - cannot use oxygen but not Aerotolerant anaerobe - cannot use oxygen but not killed if exposed; have dismutase - streptococcikilled if exposed; have dismutase - streptococci

Microaerophilic - grow best at low oxygen tension; Microaerophilic - grow best at low oxygen tension; lack cytochromes; lack catalase but have lack cytochromes; lack catalase but have dismutase; dismutase; CampylobacterCampylobacter

Transport MechanismsTransport Mechanisms

A microbial cell must take on nutrients A microbial cell must take on nutrients from its surroundings by transporting from its surroundings by transporting them across the cell membranethem across the cell membrane

Passive transport involves the natural Passive transport involves the natural movement of substances down a movement of substances down a concentration gradient and requires concentration gradient and requires no additional energy (diffusion)no additional energy (diffusion)

Osmosis is diffusion of water Osmosis is diffusion of water through a selectively permeable through a selectively permeable

membranemembrane

Form of passive transport that can Form of passive transport that can move specific substances is facilitated move specific substances is facilitated

diffusiondiffusion

DiffusionDiffusion

Transport MechanismsTransport Mechanisms Osmotic changes that Osmotic changes that

affect cells are affect cells are hypotonic solutions, hypotonic solutions, which contain a lower which contain a lower solute concentration, solute concentration, and hypertonic and hypertonic solutions, which solutions, which contain a higher contain a higher solute concentrationsolute concentration

Isotonic solutions Isotonic solutions have the same solute have the same solute concentration as the concentration as the inside of the cellinside of the cell

In active transport, substances are taken In active transport, substances are taken into the cell by a process that consumes into the cell by a process that consumes

energyenergy

In group translocation, In group translocation, molecules are altered during molecules are altered during

transporttransport

Transport MechanismsTransport Mechanisms Phagocytosis and pinocytosis are forms of Phagocytosis and pinocytosis are forms of

active transport in which bulk quantities of active transport in which bulk quantities of solid and fluid material are taken into the solid and fluid material are taken into the cellcell

Microbial Growth Microbial Growth DefinitionsDefinitions Growth - Growth -

increase in increase in numbersnumbers

Binary fission - Binary fission - method of method of reproduction reproduction used by used by prokaryotes in prokaryotes in which each cell which each cell divides; doubles divides; doubles population population (logarithmic) (logarithmic)

Microbial Growth Microbial Growth Generation time (doubling time) - time Generation time (doubling time) - time

required for a cell to divide and multiply required for a cell to divide and multiply (double) its population (20 min. - 72 hrs.)(double) its population (20 min. - 72 hrs.)

Phases of growth Phases of growth Lag - occurs at inoculation; little or no change in numbers; enzymes Lag - occurs at inoculation; little or no change in numbers; enzymes

being synthesized and cells increasing in size preparing to divide; being synthesized and cells increasing in size preparing to divide; time increased if media is coldtime increased if media is cold

Log or exponential - cell mass and number increases in logarithmic Log or exponential - cell mass and number increases in logarithmic manner; consistent rate and activity; organisms are most sensitive to manner; consistent rate and activity; organisms are most sensitive to adverse conditionsadverse conditions

Stationary - population stabilizes; production = death; may be due to Stationary - population stabilizes; production = death; may be due to accumulation to toxic wastes or decrease in nutrientsaccumulation to toxic wastes or decrease in nutrients

Death (logarithmic decline) - deaths exceed production; cells usually Death (logarithmic decline) - deaths exceed production; cells usually most resistant and often assume unusual shapes (pleomorphic)most resistant and often assume unusual shapes (pleomorphic)