Growth and Kinetics II: Microbial cultivation

Answer 1

. the common logarithm (log10) aka the decimal logarithm
. the common exponent (10x) aka the decimal exponent
. the binary logarithm (log2) – you may have a <logx (y)> or similar key in which you may have to press (to e.g. get log2 of 5) <KEY> <2> <5> to do it.
. the binary exponent (2x)– you probably have an <xy> key and would do <KEY> <2> <5> or similar to do 25.
. the natural logarithm (log e aka ln, where e is Euler’s number) the
. natural exponent (ex)
. Usually the common exponent and natural exponent are <SHIFT> and then the key for the corresponding logarithm.</SHIFT></KEY></xy></KEY>

Question 2

Cell morphologies – just the major ones

Answer 2

. 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” has nothing to do with the shape; it means “I move quickly!”
. Cocci (balls/spheres) shaped cells (some in pairs) of Staphylococcus aureus. More oval cells are coccoid. Gr. masc. n. κόκκος (kókkos), a grain, a kernel.
. Spiral shaped cells of a Thiomicrospira sp. Smaller spirals are spirilla (sing. spirillum).

Question 3

Cell division

Answer 3

• this is not mitosis/meiosis, but a completely separate type of division.
• we won’t worry much about what’s going on in fine detail – we’ve already done genome replication in
  BIOL220Z.
• 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.

Question 4

Unicellularity is very common

Answer 4

• 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 the structures on the right.

L. fem. n. sarcina, a package.
L. fem. n. capsa, a box

• beyond palisades and chains, you can have 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 gDNAcan be shared (cf. L16)

Question 5

Cell cultivation: media

Answer 5

• cells are cultivated on or in a culture medium (pl. media):
• 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:
• 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, silica gel etc but often costly or technically annoying to work with.
• usually poured as plates (for isolation/purity checking) or slants (for maintaining cultures).
• 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.

Columbia blood agar (complex medium) in Petri dishes

Mycobacterium tuberculosis growing on Lowenstein-Jensen agar
(contains malachite green to inhibit common contaminants)

Question 6

Cell cultivation: broth culture

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.
* 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.