Microbiology Chapter 6: Microbial Nutrition and Growth

Study Notes

Microbiologists study microbial growth by replicating natural conditions in the lab, focusing on chemical, physical, and energy needs.
Microbial growth refers to both metabolic activity and resulting population increase.

Chemical Needs:
- Nutrients: carbon, oxygen, nitrogen, phosphorus, sulfur, calcium, manganese, magnesium, copper, and iron.
- Macronutrients (over 95%): carbon, oxygen, nitrogen, phosphorus, and sulfur.
- Micronutrients: calcium, manganese, magnesium, copper, and iron.
Physical Needs:
- Temperature: affects protein shape and membrane fluidity.
- pH: microbes have optimal pH ranges.
Energy Needs:
- Autotrophs: use carbon dioxide as the starting block, combining it with water and sunlight (or chemicals) through photosynthesis.
- Heterotrophs: rely on pre-made organic molecules.
- Chemotrophs: use chemicals for energy.
- Phototrophs: use light for energy.

Nitrogen (N) is crucial for building biomolecules like amino acids and nucleotides, making up 14% of a microbe's dry weight.
Nitrogen limitation can limit microbial growth.
Microbes acquire nitrogen from organic and inorganic sources, and some can fix atmospheric nitrogen gas (N₂) into ammonia (NH₃) through nitrogen fixation.

Psychrophiles: thrive below 15°C, can grow at 0°C, and die at higher temperatures.
Psychrotolerants: tolerate cold but don't grow best in it.
Mesophiles: grow best between 20°C and 40°C.
Thermodurics: mesophiles that can survive brief periods at high temperatures.
Thermophiles: grow best above 45°C.
Hyperthermophiles: thrive at extremely high temperatures (above 80°C).
pH: microbes have optimal pH ranges, with acidic environments below pH 7 and basic environments above pH 7.### Impact of Hydrogen Ions on Biomolecules
Hydrogen ions can interfere with hydrogen bonding in proteins and nucleic acids, affecting their function
pH influences the structure and function of biomolecules, including enzymes and nutrients

Neutrophiles: grow best at a neutral pH (around 6.5-7.5), includes most bacteria and protozoa
Acidophiles: grow best in acidic environments (as low as pH 0.0), includes chemoautotrophic prokaryotes
Obligate acidophiles: require an acidic environment and die near neutrality (pH 7.0)
Acid-tolerant: survive in acidic environments but do not necessarily prefer them
Alkalinophiles: live in alkaline environments (up to pH 11.5), includes Vibrio cholerae

Osmosis: the diffusion of water across a semi-permeable membrane driven by unequal solute concentrations
Osmotic pressure: the pressure exerted on a membrane by a solution containing solutes that cannot freely cross the membrane
Hypotonic environment: a solution with lower solute concentration than the cell
Hypertonic environment: a solution with higher solute concentration than the cell
Microbes need water to dissolve enzymes, nutrients, and participate in metabolic reactions

Hypotonic environment: cells gain water and swell, potentially leading to lysis
Hypertonic environment: cells lose water and shrink, potentially leading to crenation
Obligate halophiles: require high salt concentrations and will burst if placed in freshwater
Facultative halophiles: can tolerate high salt concentrations but do not necessarily require them

Complex, synergistic association of microorganisms attached to surfaces
Biofilm formation: 6 steps, including settlement, attachment, EPS formation, quorum sensing, maturation, and dispersal
Impacts of biofilms: disease, protection from antimicrobial drugs, and challenges to treatment

Associations range from antagonistic (harmful) to beneficial (synergistic or symbiotic)
Antagonistic relationships: one organism harms or kills another
Beneficial relationships: synergistic (both organisms benefit but can live independently) or symbiotic (close association where members depend on each other)
Biofilms: complex, synergistic associations of microorganisms attached to surfaces

Goal: diagnose and treat disease by isolating and identifying pathogens
Importance of proper collection: avoiding contamination and protecting healthcare workers
Standard precautions: CDC guidelines to protect healthcare workers from contamination
Culturing microorganisms: 4 steps, including inoculum, medium, culture, and colony formation
Obtaining pure cultures: isolating the culprit microbe and separating it from normal microbiota

Streak plate method: most common technique, involves streaking the inoculum across a solid medium
Pour plate technique: involves diluting the sample and mixing it with agar in Petri dishes
Key differences: streak plates have colonies on the surface only, while pour plates have colonies both on and within the medium