Chapter 3: Microbial Growth

Binary fission

bacterial replication- a form of asexual reproduction in which one cell divides to form two identical cells

1. DNA replicates (both cells need DNA)

2. Cell elongation (separate into 2 cells of equal size)

3. Formation of division septum (pinch off to separate)

4. Cell separation forms 2 identical cells

Fragmentation

an alternate type of reproduction; means of asexual reproduction whereby a single parent breaks into parts that regenerate into whole new individual

- bacteria live in community that form filaments- when the filaments break, each one elongates

Budding

asexual reproduction in which a part of the parent organism pinches off and forms a new organism

- asymmetric division

- creates a normal size and a smaller size

Bacterial counts

Nn (# of bacteria after n generations)= No (# we start with)* 2n

n (# of generations)= time of incubation/doubling time

Doubling time:

E.coli: around 20 min.

M. tuberculosis: around 15-20h

M. leprae: around 14d

Lag phase

intense activity preparing for population growth, but no increase in population

- gearing up for replication

- increase cell size (budding)

- increase in metabolism

- increase in protein synthesis

Log phase

- exponential growth

- actively replicating

- most susceptible to antibiotics (targets DNA replication, protein synthesis, cell wall membranes, RNA synthesis, transcription)

Stationary phase

period of equilibrium; microbial deaths balance production of new cells

- bacteria are dying as we make new ones

- low on space, nutrients, oxygen

- bacteria go into survival mode

- start sporulation (organisms create spores to survive in unfavorable conditions)

- produce secondary metabolites (help with defense; ex. antibiotics)

- produce virulence factors (infect us more so they can stay alive)

Death phase

- exponential cell death

- increase in toxic waste

- some lyse open to help other bacteria live by releasing nutrients

- sporulation completes (releases spores)

- persister cells- refuse to die

- tend to have a lot of antibiotic resistance which may be due to plasmids that got secreted in the stationary phase which are resistant to their own antibiotics and similar ones pick up plasmids from the environment that encode antibiotic resistance to other things

- plasmids: transferring resistance genes between bacteria

Diluting bacteria for CFU (colony forming units) counting

- you have a stock of bacteria and the goal is to get individual colonies

- concentration decreases as you continue to dilute

Optical density

measures how well a medium can transmit light

- light source passes through blank sample

- when there is a bacterial suspension, there is scatter light in the tube that does not reach detector

Planktonic

free floating (can't form a community)

Sessile

describes an organism that remains attached to a surface for its entire life and does not move

- needs to be sessile to form a community

Quorum sensing

- how bacteria talk to each other

- coordination of activities in response to environmental stimuli

- occurs between microbes of the same or different species

- autoinducers: detect the population density and activates specific genes

Autoinducers

chemical signals that bacteria produce to communicate with each other and sense their population density

- gram + makes proteins and it can only secrete proteins

- gram - makes chemicals and can only secrete chemicals

- they can receive both due to receptors, but can only secrete their designated one

Biofilm formation

1. reversible attachment of planktonic cells (seconds)

2. first colonizers become irreversibly attached (second, min.)

3. growth and cell division (hours, days)

4. production of EPS and formation of water channels that flow through the community (hours, days)

- EPS= sticky extrapolymeric substance composed of nucleic acids, proteins, and lipids

5. attachment of secondary colonizers and dispersion of microbes to new sites (days, months); send some bacteria away to start a new community because it's too big

Thioglycolate medium- to measure O2 requirement

obligate aerobes, obligate anaerobes, facultative anaerobes, aerotolerant anaerobes, microaerophiles

Obligate aerobes

require normal amounts of oxygen

Obligate anaerobes

at the bottom, hates oxygen, die in the presence of oxygen unless they form spores

Facultative anaerobes

most growth at the top because they prefer oxygen, but they can grow without

- switch to fermentation when there is no oxygen

Aerotolerant anaerobes

indifferent to oxygen

- oxygen doesn't harm them, but they don't use it

Microaerophiles

all bacteria are just below the surface because they like low levels of oxygen

Capnophiles

- grow best in high CO2 and low O2

pH requirements for growth

bacteria survive best in lower pH

acidophile: acidic (ex. stomach, vagina)

neutrophile

alkaliphile (ex. sperm)

Acidophiles

grow in acidic environments

Sulfolobus sp.

Lactobacillus sp.

Neutrophiles

grow best in a narrow range around neutral pH

E. coli (in our gut)

Salmonella sp (imbalance causes disease)

Alkaliphiles

grow optimally at pH above 8.5

Vibrio cholera (ocean)

Natronobacterium sp. (archaea- pH of 10.5)

Effects of pH on DNA

denatures because it breaks hydrogen bonds between base pairs at a high pH

Effects of pH on lipids

high pH leads to breakdown of lipids; can impact membrane fluidity, stability, and cell behavior

Effects of pH on proteins

moderate changes in pH can denature proteins (charge, shape, hydrophobicity)

- changes ionization (unfolds)

- disrupting hydrogen bonds

Effects of pH on electron transport

carries in the form of protons (H+ ions) across a membrane

- low pH is disruptive

- high pH makes water and not ATP (unstable at high pH levels and breaks down into ADP)

Changes acidophiles make

- proteins have negatively charged surfaces

- hydrogen efflux pumps- remove H+ ions

- changes the lipids composition of the plasma membrane to withstand low pH

Changes alkaliphiles make

- modified lipid and protein structures so its less likely to break down from a high pH

- modified proton motive force (electron transport)

- Bacillus firmus- uses Na+ instead of H+

Psychrophiles

- optimal temp is around 15°C

- die at or above 20°C

- survive below 0°C

- live in cold lakes and the ocean floor

- antarctic ice sheets, glaciers

- bacteria in antartica

Psychrotolerant

- live between 4-25°C

- survive but no replication

- soil, freshwater, and plant surfaces in colder temperatures

Mesophiles

- moderate temperature (humans)

- 20-40°C

- 37°C is body temperature

- human body (intestines, skin)

- temperate waters, plants

- Ex. E.coli (gut), Salmonella sp., Lactobacillus sp., staph (skin)

Thermophiles

- 50°C - 80°C

- found in hot springs, geothermal soil, or composts

- Ex. Thermus aquaticus (found in hot springs- source of Taq polymerase) , Geobacillus sp.

Hyperthermophiles

- 80°C - 110°C

- found in hydrothermal vents (bottom of ocean), volcanic areas

- Ex. Pyrobolus sp., pyrodictium sp.- survives the autoclave

Effects of low temperatures on membrane structure

- membranes get stiff/less fluid- ice crystal formation because water freezes and we have water in us

- chemical reactions and diffusion slow down

Effects of high temperatures on membrane structures

- proteins and nucleic acids denature

- membranes become more fluid and impair metabolic processes

Psychrophiles adaptions

- proteins are highly hydrophobic to increase flexibility

- decreased secondary stabilizing bonds

Hyperthermophiles

- increase saturated/polysaccharide lipids to limit membrane fluidity

- increased C-G content in DNA

- increased secondary (ionic and covalent) bonds in proteins

- alter amino acid usage to prevent protein denaturing

Isotonic solution

no net movement of water particles, and the overall concentration on both sides of the cell membrane remains constant

Hypertonic solution

a solution that has a higher solute concentration than another solution; water particles will move out of the cell because the solute conc. is greater outside, and the cells shrivel up and die

Hypotonic solution

a solution that has a lower solute concentration than another solution; conc. solute is greater inside the cell so water goes into the cell, causing the cell to expand and lyse

Halotolerant

doesn't require salt for growth but can grow in high salt

Ex. S. aureus, Bacillus cereus, Vibrio cholera

Halophiles

loves salt and doesn't want to be in isotonic environment

- found in ocean and salt lakes

- adaptations: increased cytoplasmic glycerol (stops it from shriveling & lysing); efflux pumps for salt

Barophiles

need high atmospheric pressure for growth

- found at the bottom of the ocean

- ex. Mariana Trench

Photoautotrophs

use light for energy and CO2 is primary carbon source

- Ex. cyanobacteria, green sulfur bacteria

Photoheterotrophs

use light for energy but can't use CO2 as a sole carbon source

- Ex. purple non-sulfur bacteria