Chapter 7: Microbial Nutrition, Ecology, and Growth

Microbial Nutrition

process by which chemical compound (nutrients) are acquired from the environment to sustain life

Bio elements

basic requirements for life (carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, sodium, chlorine, magnesium)

Essential nutrients

substance (element or compound) an organism must get from a source outside its cells. Macronutrients and Micronutrients or trace elements

Macronutrients

required in large quantities; play principal roles in cell structure and metabolism (sugars, amino acids)

Micronutrients or trace elements

required in small amounts; involved in enzyme function and maintenance of protein structure (manganese, zinc, nickel)

Organic nutrients

contain carbon and hydrogen atoms and are usually the products of living things

• Methane (CH4), carbohydrates, lipids, proteins, and nucleic acids

Inorganic nutrients

atom or molecule that contains a combination of atoms other than carbon and hydrogen

• Metals and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide) and water

Cell contents

• 70% water

• 97% of dry cell weight is organic compound: proteins the most prevalent

• 96% of the cell is composed of 6 elements: Carbon, hydrogen, oxygen, phosphorous, sulfur, and nitrogen

Sources of the element carbon defines two basic nutritional types

• Heterotroph

• Autotroph

Heterotroph

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

Autotroph

an organism that uses CO2, an inorganic gas, as its carbon source

• not nutritionally dependent on other living things

Growth Factors

organic compounds that cannot be synthesized by an organism because they lack the genetic and metabolic mechanisms to synthesize them. Must be provided as a nutrient for survival

• essential amino acids, vitamins

Main determinants of nutritional type are:

Carbon source and Energy source

Carbon source

• Heterotroph- from other organisms

• Autotroph- uses CO2 as source

Energy source

• Chemotroph- gain energy from chemical compounds

• Phototrophs- gain energy through photosynthesis

Passive transport

does not require energy; substances exist in a gradient and move from areas of higher concentration toward areas of lower concentration.\

• Diffusion

• Osmosis

• Facilitated diffusion

Diffusion

movement of molecules down concentration gradient by random thermal motion

Osmosis

diffusion of water

Facilitated diffusion

solutes that require a carrier

Active transport

requires energy and carrier proteins; gradient independent.

• Carrier- mediated active transport

• group translocation

• Bulk transport

Carrier- mediated active transport

involves specific membrane proteins that bind both ATP and the molecules to be transported

Group translocation

transported molecule chemically altered

Bulk transport

endocytosis, exocytosis, pinocytosis

Diffusion and Molecular Motion

Net movement of molecules down their concentration gradient by random thermal movement (passive transport)

Diffusion of Water: Osmosis

Living membranes generally block the entrance and exit of larger molecules and permit free diffusion of water (passive transport) through a selectively permeable membrane.

When concentrations of the solutions differ, one side will experience a net loss of water and the other a net gain of water until equilibrium is reached

Movement of Solutes: Facilitated Diffusion

• Passive transport mechanism that utilizes a carrier protein in the membrane that will bind a specific substance

• carrier proteins exhibit specificity (they bind and transport only a single type of molecule)

• Facilitated diffusion exhibits saturation (rate of transport limited by the number of binding sites on the transport proteins)

Permeases and pumps (carrier mediated Active transport)

Specific membrane- bound transporter proteins that interact with nearby solute- binding proteins that carry essential solutes (sodium, iron, sugars)

Once a solute-binding protein attaches to a specific site in the transporter protein, an ATP is activated and generated energy to pump the solute into the cell’s interior through a special channel

Endocytosis

bringing substances into the cell through a vesicle or phagosome

• Phagocytosis

• Pinocytosis

Phagocytosis

ingest substances or cells (pseudopods)

Pinocytosis

ingests fluids and/or dissolved substances (microvilli)

Niche

totality of adaptations organisms make to their habitat

Environmental factors that affect the function of metabolic enzymes

• temperature

• oxygen requirements

• pH

• Osmotic pressure

• Barometric pressure

Cardinal temperatures

The range of temperature for microbial growth

• Minimum temperature

• Maximum temperature

• Optimum temperature

Minimum temperature

lowest temperature that permits a microbe’s growth and metabolism

Maximum temperature

highest temperature that permits a microbe’s growth and metabolism

Optimum temperature

promotes the fastest rate of growth and metabolism

Psychrophiles

optimum temperature below 15^oC; capable of growth at 0^oC

Mesophiles

optimum temperature 20^o - 40^o C; most human pathogens

Thermophiles

optimum temperature greater than 45^o C

Aerobe

utilizes oxygen and can detoxify it

• obligate aerobe

• facultative anaerobe

• microaerophile

Obligate aerobe

cannot grow without oxygen

Facultative anaerobe

utilizes oxygen but can also grow in its absence

Microaerophile

requires only a small amount of oxygen

Anaerobe

does not utilize oxygen

• Obligate anaerobe

• aerotolerant anaerobes

Obligate anaerobe

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

Aerotolerant anaerobes

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

Oxygen Requirement Determination

Cultures with reducing media that contain an O2-removing chemical, such as

thioglycolate, can help determine the O2 requirements of a microbe

The relative position of growth of bacteria that differ in O2 requirements in such

culture media provides some indication of their adaptations to O2 use

Growing anaerobic bacteria

usually requires special media, methods of incubation, and handling chambers that exclude O₂

Most microbes require some CO₂ in their metabolism

Capnophile

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

Neutrophiles

Majority of microorganisms grow at a pH between 6 and 8

Acidophiles

grow at extreme acid pH

Alkalinophiles

grow at extreme alkaline pH

Osmotic pressure

most microbes exist under hypotonic or isotonic conditions

• osmophiles

• osmotolerant

Osmophiles

require a high concentration of salt (halophile)

• obligate halophiles grow optimally in solutions of 25% NaCl but require at least 9% NaCl (salt lakes, ponds…) ex. Halobacterium, halococcus

Osmotolerant (hypotonic)

do not require high concentration of solute

• Facultative halophiles- remarkably resistant to salt ex. Staphylococcus aureus

Barophiles (pressure)

can survive under extreme pressure and will rupture is exposed to normal atmospheric pressure

Water environmental factors

only dormant, dehydrated cell stages (i.e. spores and cysts) tolerate extreme drying because of the inactivity of their enzymes

Biofilms

result when organisms attach to a substrate by some form of extracellular matrix that binds them together in complex organized layers

• Dominate the structure of most natural environments on earth

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

Division of bacterial cells occurs mainly through binary fission (transverse)

• parent cell enlarges, duplicates its chromosomes, and forms a central transverse septum dividing the cell into two daughter cells

Generation or doubling time

time required for a complete fission cycle

• generation times vary from minutes to days

Exponential growth

each new cycle increases the population by a factor of 2

growth curve

a predictable pattern of population growth over time

Stages in the normal growth curve

1. Lag phase

2. Exponential growth phase

3. Stationary phase

4. death phase

Lag phase

“flat” period of adjustment, enlargement; little growth

Exponential growth phase

a period of maximum growth when 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 and pollutants

Death phase

as limiting factors intensify, cells die exponentially

Turbidometry

most simple

• Degree of cloudiness, turbidity, of the nutrient culture media reflects the relative population size

Enumeration of bacteria

• Viable colony count

• Direct cell count- (manually or automated) counting the number of cells ina sample microscopically

Flow cytometer

sensitive device uses for counting cells in direct count