Microbiology: Chapter 7 Microbial Nutrition, Ecology & Growth


Process by which chemical substances (nutrients) are acquired from the environment & used in cellular activities

Essential nutrients

must be provided to an organism; 2 categories: macronutrients & micronutrients (trace elements)


required in large quantities; play principal roles in cell structure & metabolism; proteins & carbohydrates


trace elements; required in small amounts; involved in enzyme function & maintenance of protein structure; Manganese, zinc & nickel

Organic nutrients

contain carbon & hydrogen atoms & are usually the products of living things; Methane (CH4), carbohydrates, lipids, proteins, & nucleic acids

Inorganic nutrients

atom or molecule that contains a combination of atoms other than carbon & hydrogen; Metals & their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide) & water

Chemical Analysis of Cell Contents

70% water; proteins; 96% of cell composed of 6 elements: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorous, Sulfur: CHONPS

Sources of essential nutrients

carbon sources: Heterotroph & Autotroph


must obtain carbon in an organic form made by other living organisms such as proteins, carbohydrates, lipids, & nucleic acids


an organism that uses CO2, an inorganic gas as its carbon source; not nutritionally dependent on other living things

Growth Factors: Essential Organic Nutrients

Organic compounds that cannot be synthesized by an organism because they lack the genetic & metabolic mechanisms to synthesize them

Growth factors

must be provided as a nutrient; essential amino acids, vitamins

Main determinants of nutritional type

carbon source (heterotroph, autotroph); energy source (chemotroph, phototrophs)


gain energy from chemical compounds


gain energy through photosynthesis (light)


Oxygenic photosynthesis; Anoxygenic photosynthesis (no O2)


lithoautotrophs; survive totally on inorganic substances; ex: methanogen


chemoautotroph; produces methane gas under anaerobic conditions


majority of heterotrophs; aerobic respiration; saprobes & parasites


free-living microorganisms that feed on organic detritus from dead organisms; opportunistic pathogen; facultative parasite


derive nutrients from host; pathogens; some are obligate parasites

Passive transport

does not require energy; substances exist in a gradient & move from areas of higher concentration toward areas of lower concentration; Diffusion, Osmosis (diffusion of water) & facilitated diffusion (requires a carrier)

Active transport

requires energy & carrier proteins; gradient independent; active transport, group translocation (transported molecule chemically altered), bulk transport (endocytosis, exocytosis, pinocytosis)


net movement of molecules down their concentration gradient (passive transport)


diffusion of water (passive transport); isotonic, hypotonic, hypertonic solution

Facilitated Diffusion

passive transport; requires carrier


Eating & Drinking by cells; bringing substances into the cell through a vesicle or phagosome; phagocytosis & pinocytosis


ingests substances or cells


ingests liquids


environmental factor that influences microbes; totality of adaptations organisms make to their habitat

Environmental Factors affecting function of metabolic enzymes

Temperature, oxygen requirements, pH, osmotic pressure, barometric pressure

3 Cardinal Temperatures

Minimum temperature, maximum temperature, optimum temperature

Minimum temperature

lowest temperature that permits a microbe's growth & metabolism

Maximum temperature

highest temperature that permits a microbe's growth & metabolism

Optimum temperature

promotes the fastest rate of growth & metabolism

3 Temperature Adaptation Groups

Psychrophiles, Mesophiles, Thermophiles


optimum temperature below 15�C; capable of growth at 0�C


optimum temperature 20�-40�C; most human pathogens


optimum temperature greater than 45�C

Gas Requirements


As oxygen is utilized it is transformed into several toxic products

Singlet oxygen (1O2), superoxide ion (O2-), peroxide (H2O2), & hydroxyl radicals (OH-)

Most cells have developed enzymes that detoxify oxygen

Superoxide dismutase, catalase

If a microbe is not capable of dealing with toxic oxygen

it is forced to live in oxygen free habitats


utilizes oxygen & can detoxify it

Obligate aerobe

cannot grow without oxygen

Facultative anaerobe

utilizes oxygen but can also grow in its absence


requires only a small amount of oxygen


does not utilize oxygen

Obligate anaerobe

lacks the enzymes to detoxify oxygen so cannot survive in an oxygen environment

Aerotolerant anaerobes

do not utilize oxygen but can survive and grow in its presence

Carbon Dioxide Requirement

all microbes require some carbon dioxide in their metabolism; capnophile


grows best at higher CO2 tensions than normally present in the atmosphere


majority of microorganisms grow at a pH between 6 and 8; neutral 7


grow at extreme acid pH; acids- pH below 7


grow at extreme alkaline pH; bases- pH above 7

Most microbes exist under certain osmotic conditions

hypotonic or isotonic conditions


require a high concentration of salt


do not require high concentration of solute but can tolerate it when it occurs


can survive under extreme pressure and will rupture if exposed to normal atmospheric pressure; adapted to life under high pressure, ex: bottom dwellers in ocean


2 organisms live together in close nutritional relationships; required by one or both members; mutualism, commensalism, parasitism


type of symbiotic: Obligatory, dependent; both members benefit


type of symbiotic: the commensal member benefits; other member not harmed nor benefited


type of symbiotic: Parasite is dependent and benefits; host harmed


Organisms are free-living; relationships not required for survival; synergism, antagonism


type of nonsymbiotic; members cooperate and share nutrients to produce a result that none of them could do alone


type of nonsymbiotic; some members are inhibited or destroyed by others; actions of one organism affect the success or survival of others in the same community (competition); antibiosis

Normal microbial flora

human body is a rich habitat for symbiotic bacteria, fungi & a few protozoa; have commensal, parasitic & synergistic relationships


result when organisms attach to a substrate by some form of extracellular matrix that binds them together in complex organized layers; dominant structure of most natural environments on earth; quorum sensing

Quorum sensing

Communicate and cooperate in the formation and function of biofilms

Microbial Growth

occurs at two levels: growth at a cellular level with increase in size and increase in population

Binary fission

how division of bacterial cells mainly occurs; transverse; parent cell enlarges, duplicates its chromosome, & forms a central transverse septum dividing the cell into two daughter cells

Generation or doubling time

time required for a complete fission cycle; varies from minutes to days

Exponential Growth

each new fission cycle increases the population by a factor of 2

Rate of Population Growth

Equation for calculating population size over time; the total number of cells in the population=the starting number of cells x the number of cells in that generation

Population Growth Curve

populations typically display a predictable pattern over time

Stages in normal growth curve

Lag phase, exponential growth phase, stationary phase, death phase

Lag Phase

flat" period of adjustment, enlargement; little growth

Exponential Growth Phase

period of maximum growth will continue as long as cells have adequate nutrients and a favorable environment

Stationary phase

rate of cell growth equals rate of cell death caused by depleted nutrients and O2, excretion of organic acids & pollutants

Death phase

as limiting factors intensify, cells die exponentially


most simple; degree of cloudiness, turbidity, reflects the relative population size

Enumeration of bacteria

viable colony count, direct cell count

Direct cell count

count all cells present; automated or manual