Kinetics II and Growth

Question 1

Cell morphologies – just the major ones

Answer 1

*Rod-shaped cells= (about to divide) of Thermithiobacillus
tepidarius.
*Curved rod (shorter curved rods are vibrioid) cell (in
middle) of Thiomicrospira thyasirae. [the genus Vibrio has
curved-rod-shaped cells, thus “vibrioid”, meaning
“resembling Vibrio” –the word “Vibrio” means “I move quickly!”
*Cocci (balls/spheres) shaped cells (some in
pairs) of Staphylococcus aureus. More oval cells are
coccoid.
*Spiral shaped cells of a Thiomicrospira sp. Smaller
spirals are spirilla.

some cells can be pleomorphic so can change shape as they age

Question 2

Cell division

give an example of when cells get longer before binary fission and when they get bigger from middle to outward

Describe and give examples of the two types of binary fission

Answer 2

• this is not mitosis/meiosis, but a completely separate
  type of division.
• canonical type of division is binary fission – a cell
  gets much bigger, makes new copies of gDNA etc
  and moves them to the poles of the larger cell, a dividing septum forms between the two halves, two new cells.
• in some taxa, the cell grows bigger (before fission)
  from the middle of the cell outwards (central growth), as is the case in Escherichia coli. In others, the cell gets longer from the ends outwards (apical growth) e.g. in Corynebacterium spp.

Two types of binary fission. At the ‘short’ edge of the cell (cells get longer then divide) in Thermithiobacillus tepidarius and on the ‘long’ edge (when cell widens then divides) in a Simonsiella sp.

Question 3

Unicellularity is very common

Answer 3

• majority of known Bacteria and Archaea are unicellular but many do form transient associations or more complex structures with other cells as they are dividing, typically.
• Some cells stay unicellular and don’t interact (much)
  with nearby cells but stay in contact with them forming structures.

Two common arrangements of cocci= as tetrads/capsae
(squares) and sarcinae (cubes)
sarcina=package.
capsa=box.
Two common arrangements of rods– as palisades or chains
(can break apart). Cocci sometimes form chains.

Question 4

beyond palisades and chains
Name an example

Answer 4

Filaments and ribbons, which are more structured
and securely joined. Lamellae (sing. lamella) are
sheets of cells.
* we’re steadily learning there is a bit of a grey area
where adjacent cells can have direct cytoplasmic connections but aren’t truly multicellular.
* even gDNA can be shared

Thiothrix fructosivorans under dark-ground illumination – the bright white spots are sulfur granules in the cells. Cells are arranged in filaments with a polysaccharide sheath around each filament.

filament=like a tube on the outside (polysaccharide sheath) with cells on the inside. The cells are also longer at the base than at the ends as they divide asymmetrically
Sparky white in image are sulfur granules in cells refracting light. There can be a lot of cross (“feeding”) from adjacent cells

We can also have palisades that are transient (ribbons) more permanent. cells that are side by side and are rigid and stay together. These cells communicate with each other. More ribbons over each other can be lamellae (flat sheet).

Question 5

Cell cultivation: media

What are the two types of liquid media?
What other media can be used and how?

Answer 5

• cells are cultivated on or in a culture medium
• liquid media are used to grow planktonic cells that don’t tend to be attached to one another (unless a truly filamentous organism).
  Two key types of liquid media:
  -defined media that use contain precisely known amounts of substances that have a known molecular weight only e.g. potassium dihydrogen phosphate,dipotassium hydrogen phosphate, ammonium chloride, magnesium sulfate,
  ferric chloride, D-(+)-glucose, thiosulfate etc.
• complex media that contain anything you can’t define the molecular weight of, e.g. yeast extract, beef extract, peptone, tryptone, amylose, amylopectin etc.
• solid media (same as liquid media but set with agar to make a gel) are used to grow colonies (piles of cells each derived from a single original cell – a clonal population). Often (but not always), these are biofilms (cells attached to a surface and to other cells).
  -other gelling agents are used – some for high-temperature cultivation e.g. PhytaGel (plant extract for higher temperatures that 40 degrees), silica gel (forms a sort of glass used for difficult organisms that don’t like agar) etc but often costly or technically annoying to work with.
  -usually poured as plates (for isolation/purity checking) or slants (for maintaining cultures). Slants are good for longer incubations as petri dish agar dries out. Putting a lid makes it last longer. Slants are used for storing in a fridge. Plates are more used for seeing if the culture is pure.
  -Petri dishes used widely but sometimes we need to pour agar in more specialist containers e.g. for strict anaerobes or slow-growing organisms (as Petri dishes allow water to evaporate and the agar would dry out before growth happened).
• bright colours sometimes present are either pH indicators or dyes than can kill contaminating organisms.
  Mycobacterium tuberculosis growing on Lowenstein-Jensen agar (contains malachite green to inhibit common contaminants).

Question 6

Cell cultivation: broth culture
Describe the different types of bottles used

Answer 6

• cells are cultivated in various containers:
• Erlenmeyer flasks (250-mL normally, used for 50-mL
  culture) can be rapidly shaken to increase gas exchange and
  maintain strong growth. Used for growth curves and other
  times you want oxygen not to be limiting. Stopped with
  cotton wool or foam to let air in/gases out. Stopped with a
  vaccine stopper (e.g. SubaSeal) that can be injected through
  if growing under a non-air gas.

For smaller bottles that don’t need as good gas exchange we can use;
* universal bottles (c.30-mL) – hold about 10 mL culture and
are used mainly for testing properties of an organism.
* MacCartney bottles (ditto) also used, as are Bijou tubes
which are about 4-mL and good for making tiny agar slants.
* serum bottles are gas-tight if sealed with a vaccine stopper
– can be used to grow anaerobes, methanotrophs etc that
need non-air gas but in small volumes.

Question 7

1. Name an organism that produces curved rods.

Answer 7

Vibrio spp.,Thiomicrorhabdus spp., sometimes Thiomicrospira spp. and many more.

Question 8

2. Name an organism that produces spiral-shaped cells.

Answer 8

Thiomicrospira, if stressed/starved, Treponema pallidum, Helicobacter pylori, Magnetospirillum etc.

Question 9

3. What shape are the cells in Vibrio spp?

Answer 9

Short, curved rods.

Question 10

4. What vessel is used for liquid culture of Bacteria that grow on a gaseous alkane, if working with 20 mL culture volumes?

Answer 10

A serum bottle with abut yl rubber septum and aluminium crimp.

Question 11

5. What is the advantage over pouring agar slants versus agar plates?

Answer 11

Cheaper as use less materials, take up less space in the fridge, don’t dry out as easily.

Question 12

6. Name three complex media.

Answer 12

Nutrient agar, marine agar, Lowenstein-Jensen
agar and blood agars.

Question 13

7. Give an example of a sheathed filamentous organism.

Answer 13

Thiothrix fructosivorans.