Microbial Nutrition: Nutrients and Classifications

• Microbial nutrition is a process where chemical substances, or nutrients, are acquired from the environment to be used by microbes for cellular activities.

Essential Nutrients

• Essential nutrients are nutrients that must be provided to an organism
• Macronutrients are essential nutrients required in large quantities
  • They play principal roles in cell structure and metabolism
  • Examples include proteins and carbohydrates.
• Micronutrients, or trace elements, are essential nutrients required in small amounts
  • They are involved in enzyme function and maintenance of protein structure
  • Examples include manganese, zinc, and nickel.

Nutrients: Organic vs. Inorganic

• Organic nutrients contain carbon and hydrogen atoms and are usually the products of living things
  • Examples: methane (CH4), carbohydrates, lipids, proteins, and nucleic acids
• Inorganic nutrients are atoms or molecules that contain a combination of atoms other than carbon and hydrogen.
  • Examples include metals and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide), and water.

Chemical Analysis of Cell Contents

• 70% of a cell is water
• Proteins account for a large portion of the cell's dry weight
• 96% of the cell is composed of 6 elements: carbon, hydrogen, oxygen, phosphorous, sulfur, and nitrogen

Carbon Sources

• Heterotrophs must obtain carbon in an organic form made by other living organisms, such as proteins, carbohydrates, lipids, and nucleic acids
• Autotrophs use CO2, an inorganic gas, as a carbon source
  • They are not nutritionally dependent on other living things

Growth Factors

• Growth factors are essential organic nutrients
• 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
  • Essential amino acids
  • Vitamins

Nutritional Types

• Main determinants of nutritional type are carbon source and energy source
• Carbon Source can be heterotroph or autotroph.
• Energy source can either be chemotroph or phototroph
  • Chemotrophs gain energy from chemical compounds
  • Phototrophs gain energy through photosynthesis

Autotrophs and Their Energy Sources

• Photoautotrophs perform either oxygenic or anoxygenic photosynthesis
• Chemoautotrophs (lithoautotrophs) survive totally on inorganic substances
  • Methanogens are a kind of chemoautotroph that produce methane gas under anaerobic conditions

Heterotrophs and Their Energy Sources

• The majority of heterotrophs are chemoheterotrophs that utilize aerobic respiration
• Saprobes are free-living microorganisms that feed on organic detritus from dead organisms
  • They can be opportunistic pathogens or facultative parasites
• Parasites derive nutrients from a host
  • They can be pathogens or obligate parasites

Transport: Movement of Chemicals Across the Cell Membrane

• Passive transport does not require energy
  • Substances exist in a gradient, moving from areas of higher concentration to areas of lower concentration.
  • Types of passive transport include diffusion, osmosis (diffusion of water), and facilitated diffusion (requires a carrier)
• Active transport requires energy and carrier proteins
  • It is gradient-independent
  • Types of active transport include active transport itself, group translocation (transported molecule chemically altered), and bulk transport (endocytosis, exocytosis, pinocytosis)

Diffusion

• Net movement of molecules down their concentration gradient, a passive transport process

Osmosis

• Diffusion of water through a selectively permeable membrane

Facilitated Diffusion

• Passive transport
• Requires a carrier protein

Carrier Mediated Active Transport

• Membrane proteins (permeases) have attachment sites for essential nutrient molecules
• As these molecules bind to the permease, energy from ATP pumps them into the cell's interior through special membrane protein channels
• Microbes use these systems to transport various ions (sodium, iron) and small organic molecules

Group Translocation

• Molecule is actively captured, and along transport route, is chemically altered
• By coupling transport with synthesis, cell conserves energy

Endocytosis

• Type of active transport that involves bringing substances into the cell through a vesicle or phagosome
  • Phagocytosis ingests substances or cells
  • Pinocytosis ingests liquids

Environmental Factors

• Niche: the totality of adaptations organisms make to their habitat
• Environmental factors affect the function of metabolic enzymes
• Factors include temperature, oxygen requirements, pH, osmotic pressure, and barometric pressure.

Cardinal Temperatures

• Minimum temperature: the lowest temperature that permits a microbe's growth and metabolism
• Maximum temperature: the highest temperature that permits a microbe's growth and metabolism
• Optimum temperature: promotes the fastest rate of growth and metabolism

Temperature Adaptation Groups

• Psychrophiles: optimum temperature below 15°C and capable of growth at 0°C
• Mesophiles: optimum temperature between 20°-40°C; most human pathogens fall into this category
• Thermophiles: optimum temperature greater than 45°C

Gas Requirements

• As oxygen utilized, transformed to several toxic products, including Singlet oxygen (1O2), superoxide ion (O2-), peroxide (H2O2), and hydroxyl radicals (OH-)
• Most cells have developed enzymes to neutralize these chemicals, examples include superoxide dismutase and catalase
• If a microbe is not capable dealing with toxic oxygen it is forced to live in oxygen-free habitats

Categories of Oxygen Requirement

• Aerobe utilizes oxygen and can detoxify it
• Obligate aerobe cannot grow without oxygen
• Facultative anaerobe utilizes oxygen but can also grow in its absence
• Microaerophilic requires only a small amount of oxygen
• Anaerobe does not utilize oxygen
• Obligate anaerobe lacks enzymes to detoxify oxygen, cannot survive in an oxygen environment
• Aerotolerant anaerobes do not utilize oxygen, but can survive and grow in presence of oxygen

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

Effects of pH

• Neutrophiles: most microorganisms, grow at a pH between 6 and 8
• Acidophiles grow at extreme acidic pH
• Alkalinophiles grow at extreme alkaline pH

Osmotic Pressure

• Most microbes exist under hypotonic or isotonic conditions
• Halophiles require a high concentration of salt for growth
• Osmotolerants do not require high concentrations of solute but can tolerate it when it occurs

Other Environmental Factors

• Barophiles can survive under extreme pressure and will rupture if exposed to normal atmospheric pressure

Ecological Associations Among Microorganisms

• Symbiotic - Organisms live in close nutritional relationships, required by one or both members
  • Mutualism: Obligatory, dependent; both members benefit
  • Commensalism: The commensal benefits; other member not harmed
  • Parasitism: Parasite is dependent and benefits; host harmed
• Nonsymbiotic - Organisms are free-living, relationships not required for survival
  • Synergism: Members cooperate and share nutrients
  • Antagonism: Some members are inhibited or destroyed by others

Interrelationships Between Microbes and Humans

• The human body is a rich habitat for symbiotic bacteria, fungi, and few protozoa called normal microbial flora
• Commensal, parasitic, and synergistic relationships exist or can exist on the human body

Microbial Biofilms

• Biofilms result when organisms attach to a substrate by some form of extracellular matrix that binds them together, they form complex organized layers
• Biofilms dominate structure of most natural environments on earth
• Communicate and cooperate in the formation and function of biofilms through quorum sensing

Biofilm Formation and Quorum Sensing

• Free-swimming cells settle on a surface and remain there
• Cells synthesize a sticky matrix that holds them tightly to the substrate
• When biofilm grows to a certain density (quorum), the cells release inducer molecules that can coordinate a response
• Inducer molecule stimulates expression of a certain gene and synthesis of a protein product, such as an enzyme
• Cells secrete their enzymes in unison to digest food particles

Study of Microbial Growth

• Microbial growth occurs at two levels:
  • Growth at cellular level with increase in size
  • Increase in population
• Division of bacterial cells occurs mainly through binary fission (transverse)
• Parent cell enlarges, duplicates its chromosome, forms a central transverse septum dividing the cell into two daughter cells

Rate of Population Growth

• Time required for a complete fission cycle is called the generation, or doubling time
• Each new fission cycle increases the population by factor of 2 - exponential growth
• Generation times vary from minutes to days
• Bottom line, can grow at exponential rate, which means really fast!

Viable Plate Count

• A method used to estimate the total cell population in a flask
• Serial dilutions are made
• Plates are incubated
• Resulting colonies are counted

The Population Growth Curve

• In laboratory studies population typically displays a predictable pattern during an approximate time – growth curve
• Lag phase: Flat period of adjustment, enlargement; little growth
• Exponential growth phase: Period of maximum growth as long as cells have adequate nutrients and favorable environment
• Stationary phase: Rate of cell growth equals rate of cell death caused by depleted nutrients and O2 with excretion of organic acids and pollutants
• Death phase: As limiting factors intensify, cells die exponentially

Methods of Analyzing Population Growth

• Turbidometry is the most simple
  • Measures degree of cloudiness, turbidity, and reflects relative population size (estimate)
• Enumeration of bacteria
• Viable colony count
• Direct cell count, count all cells present; automated or manual

Explore microbial nutrition, where microbes acquire chemical substances for cellular activities. Learn about essential nutrients like macronutrients and micronutrients, and the differences between organic and inorganic nutrients. Understand how these nutrients support microbial life processes.