Microbio 2.0 Lec 4 (EXAM 2) - INCOMPLETE

Cell Nutrition

Nutrients → supply of elements req. by cells for growth

• Macronutrients → LARGE amnt needed

• Micronutrients → SMALL amnt needed

Heterotrophs → req. organic carbon

Autotrophs → syn. organics from CO2

Chemical Make Up of a Cell

Carbon , Oxygen, Nitrogen, Hydrogen, Phosphorus, Sulfur → req. BY ALL LIFE (~96% of dry weight of bacterial cell)

• K, Na, Ca, Mg, Cl, Fl (~3.7% dry weight)

• Nitrogen used for protein and nucleic acid (nitrogen fixation)

  • nearly all microbes can use ammonia (NH3) and many use nitrate (NO₃^-)

  • Phosphorus used for nucleic acid

  • Sulfur used for sulfur containing amino acids

    • EX: vitamins (biotin, thiamine, lipoic acid)

  • K is for enzymes

  • Mg used to stabilize ribosomes, membranes, and nucleic acid

  • Ca used for cell wall

  • Na important for marine organisms

  • Fe used for cellular resipiration, related oxidation-redux reactions*****

    • BACTERIAL cells have a much higher binding affinity for iron than human cells

Growth Media and Lab Culture

Classes of Culture Media

• Defined media → exact comp. is known

• Complex media → digests of microbial, animals, or plant products

• Selective Medium → contains compounds that inhibit growth of some microbes but not others

• Differential Medium → contains indicator that detects particular metabolic reactions

  • EX: MSA (mannitol Salt Agar) → selective for staph bacteria and differentiates between staph species

    • mannitol fermentation

Lab Culture

• can be liquid or sold

  • solid media is prepped via addition of agar to liquid media

• Colony morphology → used to identify microorganisms and determine if culture is pure, contaminated, or mixed

• Aseptic Technique → transfer w/o contamination

  • Pure cultures contain a single microbe usually req. streak plate technique w. inoculating loop

Microscopic Counts of Microbial Cell #

Total Cell Count

• microscopic cell count → observing and enumerating cell present

  • Potential Problems:

    • experimental error (might’ve not been fully homogenized)

    • human error (miscount or double counted)

    • is the cell dead or alive (req. special staining)

Phylogenetic stains can determine proportions of bacteria and archaea in a sample

Viable Counting of Microbial Cell #

Viable (alive/lving) count → measurement reproducing population

• 2 Ways to perform viable plate count:

  • Spread-plate method

  • pour-plate method

  • is reported in cfu

• Diluting a Sample

  • 10 fold, serial/successive dilutions needed for dense cultures

• Plate counts are: quick and easy, used in food, dairy, medical, and aquatic microbiology, and highly sensitve

• Great plate count anomaly → naturally selected samples reveal more organisms than recoverable samples on plates bc you can’t tell if cells are dead or alive

Turbidimetric Measures of Microbial Cell #

Cell suspensions are turbid (cloudy) bc cells scatter light

• turbidity measurements are rapid, widely used for estimates

• is measured w/ spectrophotometer → units in optical density (OD) @ specific wavelength

Microbial Growth Cycle

Growth → increase in # of cells

• Binary Fission → cell division following enlargement of a cell to twice original size

Septum → partition between dividing cells, pinches off between 2 daughter cells

Generation (doubling) time → time req for cells to double in #

• EX: E. Coli → 20 min

Microbial Growth Cycle

• Batch culture → closed-system microbial culture of fixed volume

  • Typical growth curve:

    • lag phase → time needed for biosynthesis of new enzymes

    • exponential/growth phase (shortest time) → doubling population @ regular intervals, GROWTH will continue until conditions can no longer sustain growth

    • stationary phase

    • decline/death phase (longest time)

  • growth + stationary phase growth limited by nutrient depletion OR waste accumulation

Continuous Culture + Biofilm Growth

Continuous Culture → open system

• Chemostat → most common type of continuous culture device where know volume added while spent medium is removed at same rate

  • this keeps microbes fresh + constantly growing while removing waste\

  • Dilution rate (D) : F / V

  • experimental uses of chemostat → used to study physiology, microbial ecology + evolution, enrichment + isolation of bacteria from nature

• Steady state → cell density + substrate conc do not change over time

Biofilm Growth

Planktonic growth → floating (suspension of free living cells)

Sessile Growth → attached to surface

• can develop into biofilms

  • important in medical + industrial app

  • diff prop than planktonic cells

Biofilms → cells enmeshed in POLYSACCHARIDE MATRIX attached to surface

• Stage of Biofilm development:

  • Planktonic cells attach (flagella, fimbriae, pili)

  • colonization

  • development

  • dispersal

• EX: psudomona aeruginosa (very well known for forming biofilms + rez to antibiotics)

• Microbial Mats → multilayered sheets w/ diff organisms in each layer

  • EX: hotsprings

  • responsible for cavities, gum disease, plug + corrode pipes, form in fuel tanks + ship hulls, joint infections + medical devices

Alternatives to Binary Fission

Hyphae → long, thin filaments of actinomycetes G(+) filamentous bacteria

Mycelia → weaved hyphae

Arthrospores → survival structures formed from mycelia

Temp Classes of Microorganisms

Cardinal Temps

• minimum, optimum, and maximum temp @ which an organism grows

• @ optimum all/most cellular components are functioning @ max rate

  • Psychrophiles (cold) ; optimal growth ~15C, max 20C, minimum 0C

  • Mesophiles (optimal temp)

  • thermophiles (hot temp)

  • hyperthermophile (very hot temps)

Microbial Life in Cold

• Extremophiles → organisms that grow under very hot or cold conditions

• Psychrotolerant → can grow @ 0C but have optima of 20 - 40C

  • isolated from soils + waters in temperate climates and food @ 4C

• prod of enzymes that function optimally in the cold

  • more alpha-helices than beta-helices → greater flexibility for catalysis @ cold temp

  • more polar + fewer hydrophobic amino acids

  • cytoplasmic membrane functions @ low temps

  • cold shock proteins

  • cryoprotectants (EX: antifreeze proteins, certain solutes) prevents form of ice crystals