(Lecture 6) Overview of Bacterial Growth

where does most of the dry weight of the cell come from?

Protein

How much more of RNA than DNA is there in the cell?

Roughly 7 times the amount

What is the final portion of a cell mostly comprised of?

Lipids (fats), polysaccharides (sugar), and lipopolysaccharides (fatty sugars).

What is the most prevalent element by dry weight and around how much of E. coli's dry weight?

Carbon

What are the essential cations /anions for most life?

potassium (K), sodium (NA), calcium (CA), magnesium (MG), and chlorine (CL)

How do bacteria replicate?

Symmetrical division

What is symmetrical division?

this division creates two duplicate daughter cells from an initial mother cell. The most common mechanism for this is binary fission

What is binary fission?

The elongation and separation of a single microbial cell into two daughter cells,

What is cell elongation?

Increase in cell size due to growth and the creation of cellular structures (anabolism)

What is septum formation?

A partition forms between dividing cells, separating the daughter cells.

What is generation?

The process of one cell dividing into two cells.

What is generation time?

The time it takes for a newly form cell to divide into two cells.

How long is the generation time for E.coli?

20 minutes

How long is the generation time for V.natrienges?

9.8 minutes?

How long is the generation time for M.tuberculosis?

24 hours.

Ho does each generation divide?

The population increases exponentially.

How much bacteria is 10 generations?

1000 bacteria

How much is 20 generations?

1 million bacteria

How much is 30 generations?

1 billion bacteria.

Does bacteria die off during division?

Yes.

What is a growth curve?

The way the change in the number of bacteria over time can be graphically represented.

What is the lag phase?

When microbes enter a new medium, they must alter their metabolic state to respond to the new conditions.

What is exponential phase?

The growth period when cells are doubling at regular intervals. These cells are considered metabolically identical.

What is the stationary phase?

There is no net increase/decrease in population. Cells are dying and being created at the same rate. Cellular metabolism has shifted to maintenance and survival.

What is decline phase?

The rate of cell death is greater than the rate of cell division. Overall cell number decreases.

Various factors can alter the growth rate of bacteria, and even their viability in the environment. How does nutrient variability affect growth conditions?

Essential nutrients may vary between different species of bacteria.

Various factors can alter the growth rate of bacteria, and even their viability in the environment. How does temperature affect growth conditions?

Some bacteria prefer hotter temperatures, while others prefer colder climates.

Various factors can alter the growth rate of bacteria, and even their viability in the environment. How does the presence of oxygen affect growth conditions?

Oxygen may be essential, non-essential, or toxic to different bacterial species.

Various factors can alter the growth rate of bacteria, and even their viability in the environment. How do pH levels affect growth conditions?

Some bacteria may prefer acidic or basic environments while others prefer neutral pHs

Are all microbes temperature dependent or only some of them?

All are temperature dependent.

What is a minimum cardinal temperature?

The temperature below which cellular growth cannot occur.

What is an optimal cardinal temperature?

The temperature at which growth is most rapid. Doubling time is at its shortest.

What is maximum cardinal temperature?

The temperature above which denaturation of essential cellular components and enzymes begin, resulting in cell death.

What is the optimum growth temperature for psychrophiles?

Grow better at lower temperatures. (8 degrees) - Below 15 degrees and a maximum below 20

What is the optimum growth temperature for mesophiles?

Grow best at temperatures found in the human intestine, terrestrial and aquatic environments, and tropical latitudes. (37 degrees)

What is the optimum growth temperature for thermophiles.

Grow better at high temperatures (48 degrees)

Where do psychrophiles often grow?

Within and under sea ice. They are also found on the faces of permanent snowfields and glaciers, resulting in a distinct pigmentation.

Why do psychrophiles contain an increased number of a helices over beta sheets?

Alpha helices have more flexibility than beta sheets, which counteracts the cold induced rigidity

Why do the cytoplasmic membranes of psychrophiles have more unsaturated fatty acids?

To increase fluidity.

What temperature can thermophiles can survive, where no bacteria can?

Thermophiles can survive temperatures exceeding 100 degrees, whereas no bacteria have been found to survive above 95 degrees.

What are the adaptations that thermophiles have that allow them to survive high temperatures?

They contain GC-rich DNA sequences which help prevent denaturation of DNA.

How do thermophile form strong ionic bonds?

They produce heat stable proteins which contain an increased number of basic amino acids.

How do thermophiles prevent unfolding?

They contain highly hydrophobic interiors.

When did an oxygen rich atmosphere begin?

Only 2.3 billion years ago, 1.5 billion years after life had begun.

What is the benefit of oxygen?

Oxygen is an excellent electron acceptor enabling large amounts of ATP generation seen in aerobic respiration.

What is the cost of oxygen?

Oxygen produces highly toxic by-products in cellular processes called reactive oxygen species (ROS)

What generates ROSs?

The reduction of oxygen to water.

Examples of strong oxidizing agents.

Superoxide, hydrogen peroxide, and the hydroxyl radical

What do ROSs do?

Damage cellular components, organic compounds, and macromolecules by oxidation

How are ROSs converted to less damaging byproducts?

Microbes, like catalase and peroxidase, that live in environments with oxygen produce enzymes which convert these ROS to less damaging byproducts.

What does superoxide dismutase do?

It converts superoxide into the less toxic hydrogen peroxide.

What are aerobes?

Can use oxygen as a terminal electron acceptor

What are anaerobes?

Cannot use oxygen as a terminal electron acceptor.

What are obligate aerobes (A)?

Oxygen required for growth.

What are facultative aerobes (C)?

Can use oxygen but can also grow under anaerobic conditions,

What are microaerophilic aerobes (D)?

Oxygen required at percentage less than 21% (atmospheric).

What are aerotolerant anaerobes (E)?

Bacteria can tolerate the presence of oxygen

What are obligate anaerobes (B):

Oxygen is lethal to bacteria