Gene conserversion
A gene is conserved if it stays similar across different species over time.
This means the gene is important for survival, so evolution keeps it mostly unchanged.
Microbial Diversity
- can live anywhere on earth because they adapt to every temperature
-Temperature: Some thrive in extreme heat (thermophiles) or cold (psychrophiles).
-pH:Acidophiles: love acidic environments (low pH).
Alkaliphiles: thrive in basic conditions (high pH).
Neutrophiles: prefer neutral pH (~7).
Water Availability, Oxygen, Pressure, Nutrient Composition etc
temperature classes of microbes
psychrophile: cold loving
mesophile: room temperature (39)
thermophile: heat loving
hyperthermophile: extreme heat loving
Methanogenium frigidum – psychrophilic methanogen
Methanogenium frigidum survives in freezing, oxygen-free conditions by making methane from hydrogen and carbon dioxide — a metabolism completely opposite to humans, who need warmth, oxygen, and organic food for energy.
growth rate : minimum
membrane gelling(At very low temperatures, the lipid bilayer of the cell membrane becomes rigid (like gel), transport processes so slow that growth cannot occur
growth rate : optimum
enzymatic reaction occurring at maximum possible rate
growth rate : maximum
protein denaturation, collapse of cytoplasmic membrane , thermal lysis(rupture of cell wall)
Deep-sea microbes
- can live at ~300 atmospheres pressure (~4,408 psi), Found near black smokers (underwater hydrothermal vents, “mineral chimneys” 3000 m below surface).
-environments often have high temperatures near vents or very cold water further away.Microbes must adapt to both high pressure and temperature extremes.
Microbial Adaptations to Heat and Pressure
Bacteria: Increase the ratio of saturated fatty acids → makes membranes less fluid and more stable under heat.
Archaea: Some use a lipid monolayer instead of a bilayer → extremely stable at high temperatures.
Heat-shock proteins (HSPs): Help refold damaged proteins.
Heat-stable proteins: Naturally resistant to denaturation at high temperatures.
High G+C content: More Guanine-Cytosine pairs → 3 hydrogen bonds vs 2 in A-T → DNA is more thermally stable.
Positive supercoils (archaea): DNA is twisted tightly to resist unwinding or melting at extreme heat.
Microbial Diversity in Ocean Zones
-Cold ocean temperatures decrease plasma membrane fluidity, making membranes stiff.
-Microbes increase polyunsaturated fatty acids in their membranes → keeps them fluid and functional even in cold water.
-Microbes adapt their enzymes to work efficiently at low temperatures, more flexible.
Salinity and Microbial Adaptation
A halophile (“salt-loving” microorganism), requires very high salt levels to grow (3.5-5M NaCl), Found in places like the Dead Sea. Maintains internal salt balance and enzyme adapt to work there.
ex Halobacterium salinarum; S-layer(surface layer) with active transporters, Contains >4 M potassium chloride (KCl) — this matches the salty surroundings, preventing water loss.
pH and Microbial Diversity
Most microbes can only tolerate a narrow pH range — usually 2–4 pH units above or below their optimum pH.
pH affects enzyme activity, membrane stability, and nutrient transport.
ex; (Picrophilus oshimae)-acidophiles
(Natronbacterium gregoryi)-alkaliphiles
Radioactivity and Microbial Survival
Deinococcus radiodurans can survive up to 15,000 grays of radiation. Humans are killed by just 10 grays.
How It Survives Radiation- DNA Repair System:
It has four copies of its genome → gives it backup DNA templates to repair breaks caused by radiation.
These copies make DNA repair fast and accurate, even after massive damage.
Manganese Complexes:
Contains manganese-based antioxidant complexes that protect proteins and enzymes from radiation damage.
These act like a shield against oxidative stress.
Protective Pigments:
Produces pigments (like carotenoids) that absorb UV radiation and reduce oxidant damage.
Possible Biofilm or Capsule:
These outer layers may provide extra protection from radiation, drying, and other stresses.
why should we study microbes physiology
-to understand how they interact with the world
-for medicine purpose , could be how to use or protect against them
-see how they live in harsh environments and adapt
-food safety and water safety
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What is the relationship between phylogeny, gene conservation, protein function, and structure?
Phylogeny = evolutionary relationships among organisms or genes.
Gene conservation = genes that stay similar across species because they’re vital for survival.
Protein function conservation = conserved genes make proteins that keep the same job in different species.
Structure/model = protein structure often stays the same to preserve function; models help compare evolution and predict function.
cyanobacteria vs plant cell
Both cyanobacteria and plant cells do photosynthesis, but cyanobacteria are prokaryotic (simpler structure no nucleus or membrane-bound organelles), while plant cells are eukaryotic and have chloroplasts (which preform photosynthesis)
What makes microbes metabolically unique?
They have varied metabolisms and can perform many different biochemical reactions depending on their environment. Some eat organic matter (heterotrophs).Some use sunlight (phototrophs). Some use chemicals like hydrogen or methane (chemotrophs).
What is compartmentalization in microbes?
It’s when microbes separate or organize different metabolic processes within specialized structures or regions of the cell.
Compartmentalization; Multienzyme granules
Example: Pyruvate Dehydrogenase Complex (PDC)
This enzyme complex performs a key reaction at the end of glycolysis:
Pyruvate→Acetyl-CoA+NADH+CO₂
It’s made of three enzymes (E1, E2, E3), and many copies of each — forming a massive multienzyme structure (like a mini factory)..pyruvate dehydrogenase complex acts like a functional compartment(it organizes certain biochemical processes in space for them to react more efficiently.)
Compartmentalization: Inclusion Bodies
Inclusion bodies are storage compartments inside microbial cells.
They are not surrounded by a membrane, but they serve as special areas where the cell stores or organizes important materials.
Compartmentalization: Intracellular Membranes
Some microbes create extra internal membranes to separate specific chemical reactions from the rest of the cell.
These are not organelles like in eukaryotes, but they serve similar purposes — giving certain reactions their own space.
Nitrogen Fixation (anaerobic process)
Methanotrophs(internal membrane to seperate from O2)
Methanotrophs(internal membrane packed with enzymes that help break down methane. and give energy)
Phototrophs- These use light for energy and have internal membranes containing pigments (like chlorophyll) to absorb light efficiently.
What roles does the cell membrane play in microbial compartmentalization?
The cell membrane acts as a functional compartment where key processes occur:
Transport: controls movement of molecules in/out of the cell
Energy generation: site of the electron transport chain and ATP synthesis
Sensory proteins: detect environmental signals
Lipid rafts: organized zones for specific functions
🧠 It’s both a boundary and a specialized area where essential cellular processes are organized.
Compartmentalization: Periplasm
The periplasm is the space between the inner and outer membranes in Gram-negative bacteria.
It contains salts, proteins, and oligosaccharides for nutrient transport, cell wall synthesis, and osmotic protection.
Gram-negative: has a true periplasmic space.
Gram-positive: lacks an outer membrane; only a small periplasm-like zone exists.
What are the main functions of the cell wall in microbial compartmentalization?
The cell wall helps organize and support key processes:
Transport of molecules
Sensory proteins for environmental detection
Macromolecular machines (flagella, pili) anchored in the wall
Extracellular enzymes that digest nutrients outside the cell
