Bacterial growth

At which temperature do psychrophiles grow?

4C

At what temperature do mesophiles grow?

37C

At what temperature do thermophiles grow?

70C

At what temperature do extreme thermophiles grow?

106C

What factors increase membrane fluidity?

high content of unsaturated, polyunsaturated and methyl-branched fatty acids

shorter acyl-chain length (limits membrane cohesion/homogeneity)

How do psychrophiles adapt to cold temperatures?

increase membrane fluidity

produce anti-freeze proteins (AFPs)

production of cryoprotectants

production of cold adapted enzymes

How do AFPs function?

 bind to small ice crystals to inhibit their growth by covering water-accessible surfaces of ice

How do cold adapted enzymes allow for greater membrane flexibility?

higher proportion of a helices, less weak bonds and interdomain interactions

How do thermophiles adapt to high temperatures?

Genome protection

Existence of thermostable chaperonins

Production of thermostable proteins

Modification of the membrane composition

How is the genome protected in thermophiles?

• Stabilization of DNA by DNA-binding proteins

• Introduction of supercoils by reverse DNA gyrases

• Resistance to denaturation favoured by high G-C %

How does the modification of membrane composition allow the adaptation of thermophiles to high temperatures?

Ether-linked phospholipids = stronger so avoid breakage

Single lipid layer (glycerol tetraethers) = thermally stable

How do thermostable proteins function in high temperatures?

hydrophobic interactions, increased proportion of ionic interaction

What are thermostable chaperonins? How do they allow thermophiles to live in high temperatures?

protein complexes that help proteins fold and are resistant to high temperatures

where proteins could be dysfunctional and unfolded, chaperonins allow proteins to fold and work properly

Name an example of thermostable chaperonin? In what type of organism can these be found?

thermosome

Archaea like Pyrodictium abyssi

What are cardinal temperatures?

minimum, optimum, and maximum temperatures that define the limits of growth and development

What are the 5 requirements for bacterial growth?

• temperature

• pH

• nutrients

• Oxygen

• Osmotic pressure

What are the 3 types of bacteria called depending on their optimal pH for growth?

• acidophiles

• neutrophiles

• alkaliphiles

Name some metabolic adaptations of acidophiles

• Hydrogen drives ATP synthesis and force power motility + substrate symport

• membrane impermeability/stability through tetraether lipids

• H/Na+ antiporters maintain pH below external pH

What types of organisms are adapted to live in pH of volcanic soils and waters ?

acidophiles bc pH is around 1

What types of organisms are adapted to live in pH of alkaline lakes?

alkaliphiles bc pH is around 10

Name some metabolic adaptations of alkaliphiles

• sodium drives ATP synthesis, its motive force powers motility and drives substrate symport

• H/Na+ antiporters scavenge protons

• sodium is secreted and pumped through decarboxylases and respiratory chains

Which ion is alkaliphile metabolic activity mainly dependent on?

Sodium

Which ion is acidophile metabolic activity mainly dependent on?

Hydrogen

What are 4 types of bacteria classifications depending on their optimal osmotic pressure?

• nonhalophile

• halotolerant

• halophile

• extreme halophile

Name an example of nonhalophile and a halotolerant bacteria

Escherichia coli // staphylococcus aureus

Name an example of halophile vs extreme halophile bacteria

aliivibrio fischeri vs halobacterium salinarum

In acidophiles, what powers the flagellar motion? And in alkaliphiles?

protons

sodium

What is the osmotic pressure of water? What are therefore most aquatic bacteria?

0.5M so most will be halotolerant/halophile

What domain of life are the main extreme halophiles in?

Archaea

What is osmotic pressure?

pressure caused by water at different concentrations due to the dilution of water by solutes like salts

From what Molarity of NaCl are bacteria considered halophiles? Extreme halophiles?

around 1 - 1.5 M vs >3.5 M

From what Molarity of NaCl are bacteria considered nonhalophiles? Halotolerant?

Under 0.5M, around 0 - 1 M

What are 3 responses to osmotic stress in bacteria?

Regulation of water movements by passive diffusion and aquaporins

Production of compatible solutes to cope with high osmolarity (betaine, proline, glutamic acid…)

Release of solutes by mechano-sensitive channels

What can salt be required for in halophile bacteria?

Stabilization of the S-layer glyco-protein by Na⁺ ions

Accumulation of K+ as a compatible solute (>4M in the cell!)

both = cell membrane stability

What types of nutrients to bacteria require for growth?

-Nitrogen

-Sulfur

-Phosphorus

-Some vitamins

-K⁺, Ca²⁺ Mg²⁺ (cofactors)

-Trace elements (Fe, Cu, Zn…)

What are 2 types of bacteria depending on how they acquire energy?

• phototroph through sunlight

• chemotroph through preformed molecules

What are 2 types of electron sources for bacteria?

organic molecules (carbon) or inorganic (no carbon so like nitrate)

What are 2 types of carbon sources for bacteria?

organic compounds like amino acids, carbohydrates

inorganic compounds like CO2

What distinguishes organotrophy from autotrophy?

obtain hydrogen/electrons from organic substrates to perform respiration (basically eat food)

converts abiotic sources of energy into energy stored in organic compounds (basically make their own food)

What distinguishes a heterotroph from an autotroph?

source of their energetic compounds for nutrition

can’t produce its own food so must obtain organic carbon from other organisms vs convert abiotic sources of energy into energy stored in organic compounds

What’s the difference between a heterotroph and an organotroph?

can’t produce its own food so must obtain organic carbon from other organisms vs specifically gets its energy breaking down organic compounds

so an organotroph is a specific type of heterotroph

When considering heterotrophs and autotrophs, which are termed producers vs consumers?

producer = auto

consumer= hetero

What distinguishes organotrophs from lithotrophs?

get energy from organic compounds /vs/ get energy from inorganic compounds

Which molecule is an especially good terminal acceptor of electrons?

oxygen

Name enzymes that detoxify reactive oxygen species by converting H₂O₂ into H₂O

catalase / peroxidase

How do superoxide dismutase and superoxide reductase detoxify O₂^- ?

convert O2- in H2O2 then H2O (with help of catalase)

What are toxic forms of oxygen?

Reactive Oxygen Species including superoxide, hydrogen peroxide, hydroxyl radicals

Where does ROS come from and what functions des it have? How is it dealt with in bacteria?

by-product of cellular respiration in mitochondria

role in signalling pathways (cell cycle, phagocytosis, enzyme activation)

detoxified by various enzymes

What determines which enzymes are used to detoxify ROS?

the bacteria species and the enzymes they have

What are the 5 types of bacteria depending on how much oxygen they require to grow?

• obligate aerobes

• facultative aerobes

• microaerophiles

• anaerobes aerotolerant

• obligate anaerobes

What are the oxygen requirements for obligate aerobes?

catalase + superoxide dismutase, exclusively uses O₂ for respiration

What are the oxygen requirements for facultative aerobes?

catalase + superoxide dismutase, can use O₂ for respiration

What are the oxygen requirements for microaerophiles?

require O₂ for respiration

What are the oxygen requirements for anaerobes aerotolerant?

only superoxide dismutase, do not use O₂ for respiration

What are the oxygen requirements for obligate anaerobes?

no oxygen required

What are ways of directly measuring bacterial growth?

microsopy, flow cytometry, plating

What are ways of indirectly measuring bacterial growth?

optical density, dry weight, production of metabolites

What are 3 factors determining bacterial metabolic types?

• Energy (light/preformed molecules)

• Electrons (organic/inorganic)

• Carbon  (organic/inorganic)

What does the sensitivity of bacteria to oxygen rely on?

(i) the use of O₂ as an electron acceptor and 

(ii) the production of enzymes detoxifying ROS

What are limitations to optical density as a way to measure bacterial growth? (4)

- requires high cell densities (>10⁷ cells/ml)

- does not distinguish live vs dead cells

- OD values differ depending on organisms

- does not work with molds and filamentous bacteria

What does optical density measure? How?

unscattered light

light through sample with cells

photocell measures the unscattered light, spectrophotometer gives the OD

Describe what a bacterial growth curve is?

plot the amount of bacteria in a culture as a function of time, shows exponential/logarithmic growth through 4 distinct growth phases

What are the 4 phases of bacterial growth?

• lag phase

• log phase

• stationary phase

• death phase

Describe the lag phase of bacterial growth

metabolism starts but no division - stable level of cells

Describe the log phase of bacterial growth

exponential increase in bacterial population - this logarithmic growth is due to multiplication by binary fission

Describe the stationary phase of bacterial growth

microbial deaths balance production of new cells - stable level of cells

Describe the death phase of bacterial growth

population is decreasing

Beyond what temperature can mesophiles no longer grow?

70 C

What types of bacterial proteins contain more alpha helices?

psychrophile ones (optimal growth in cold temp.)

Does the cytoplasmic membrane of psychrophiles or thermophiles contain a higher proportion of saturated fatty acids ?

thermophiles

At what temperatures is super coiled DNA found?

high, 95 to 107 C

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