Lab 24, part 1

Bacteria

-Bacteria are prokaryotes.

prokaryotes: species with cells lacking membrane-enclosed organelles. Unicellular; cell size of about 1 micrometer in diameter; DNA molecule in nucleoid region, not nucleus; reproduce by binary fission; simpler flagella; wide metabolic diversity.

eukaryotes: species with cells that have membrane-enclosed organelles. Multicellular; cell size of about 10 micrometers; DNA in chromosomes in nucleus; cell division via mitosis and meiosis; more complex flagella; less metabolic diversity.

Domain Archaea (with Kingdom Archaebacteria)
-extremophiles

Domain Bacteria (with Kingdom Bacteria)
-Distributed more widely than any other group of organisms.
-Have cell walls which give them three distinct shapes:

1) Bacillus (rod-shaped)
2) Coccus (spherical)
3) Spirillum (spiral)



-Mostly Heterotrophic, decomposers that feed on dead organic matte and release nutrients locked in dead tissue.

-Some Autotrophic, via photosynthesis.

-Fission: asexual reproduction in which a cell's DNA replicates and the cell pinches in half without the nuclear and chromosomal events associated with mitosis.

-Conjugation: genetic recombination in which all or part of the genetic material of one bacterium is transferred to another bacterium and a new set of genes is assembled.

-Some bacteria are pathogenic and cause diseases: pneumonia, tuberculosis.

-Gram Stain: a helpful process that correlates with the sensitivity of a bacterium to antibiotics.
1) Gram-negative: bacteria that have a thinner cell wall that does not retain the crystal violet dye applied in the process of staining. After the process, they will be red from safranin. (Have a lipopolysaccharide coating).
2) Gram-positive: bacteria that have a thicker cell wall that does retain the crystal violet dye. (Have not lipopolysaccharide coating, just peptidoglycan).

-Bacterial Colony Morphology: Can help identify bacteria by looking at shape, color, size, texture and margins of a colony
1) Form:
a) Circular
b) Pinpoint
c) Irregular and spreading
d) Filamentous
e) Wrinkled

2) Margins:
a) Smooth (entire)
b) Wavy (undulate)
c) Lobate
d) Irregular (erose)
e) Filamentous

3) Elevations:
a) Flat
b) Raised
c) Convex
d) Umbonate







-Nitrogen Fixation By Bacteria: the process by which atmospheric nitrogen (N₂) is transformed into other nitrogenous compounds that can be used as nutrients by plants. Because the triple bond in the nitrogen molecule is hard to break, plants depend on bacteria to do this.

-Use an enzyme called nitrogenase along with ATP, energized electrons, and water to convert N₂ to ammonia (NH₃). Ammonia can be absorbed by plants and used to make proteins and other macromolecules.

Lab Example: Rhizobium, grows on the roots of legumes. Form nodules that transfer ammonia to the host plant while the host plants supplies the bacteria with sugars and other nutrients.



Bacterial Sensitivity to Inhibitors:
-Determined by Sensitivity Plates: a petri dish of solid medium uniformly inoculated with a bacterium.



After inoculation, four to eight small paper disks that have each been soaked in a different antibiotic are placed equidistant on the inoculated surface. After 24 hours, an effective antibiotic will produce a visible halo of clear surface around the disks where it inhibited growth of bacteria. If the antibiotic was ineffective, the bacteria will grow to the edge of the paper disk.