BacteriaAn Overview
BacteriaBacteria is the plural of
bacteriumProkaryotic cells – no true
nucleusHave one double stranded
chromosomeMay have additional DNA called a
plasmidReproduce by binary fissionMost are benignSome are pathogenic
KingdomsTwo kingdoms include prokaryotic
cellsArchaebacteria
◦Extremophiles◦Methanogens - intestines◦Halophiles - salt◦Thermophiles – heat tolerance◦May have been on Earth for 3.5
billion years
Eubacteria – all other bacteria
ArcheabacteriaThermophile research in
Yellowstone has also proved benefical to the field of astrobiology.
Many scientists believe that thermophiles are most closely related to the primordial origin of life and can provide insight into early Earth as well as expand possiblities for life elsewhere in the universe
Archaebacteria
Filamentous BacterisYellowstone
Thermophile matsGrand Prismatic
Archaebacteria
Halophilic bacteria surviving in salt crystals.Owens Valley, California
Salt crust is colored red by dense colonies of halophilic archaebacteria. Sierra Nevada
Characterizing EubacteriaBacteria can be characterized by
shape
Characterizing BacteriaBacteria is also classified by their
oxygen requirementsAerobic Bacteria require oxygen
to support reproduction◦Esherichia coli
Anaerobic bacteria reproduce in the absence of oxygen◦Listeria◦Clostridium botulinum
Characterizing BacteriaFacultative bacteria reproduce
either in the presence or in the absence of oxygen.◦Salmonella◦Staphylococcus aureus◦Bacillus cereus
Characterizing BacteriaBacteria secrete a covering for
themselves - cell wallDo not contain cellulose like plant cell
wallsMostly made of peptidoglycan
(polypeptides bonded to modified sugars)
the amount & location of the peptidoglycan are different in the two possible types of cell walls, depending on the species of bacterium
Characterizing BacteriaSome antibiotics, like penicillin, inhibit the
formation of the chemical cross linkages needed to make peptidoglycan.
These antibiotics don’t outright kill the bacteria, but just stop them from being able to make more cell wall so they can grow.
That’s why antibiotics must typically be taken for ten days until the bacteria die (unable to grow)
If a person stops taking the antibiotic sooner, any living bacteria could start making peptidoglycan, grow, and reproduce.
Characterizing BacteriaDr. Hans Christian Gram, a
Danish physician, invented a staining process to tell the two types of bacteria apart, and in his honor, this process is called Gram stain.
Gram Stainthe amount of
peptidoglycan in the cell walls of the bacteria determine how those bacteria absorb the dyes with which they are stained
bacterial cells can be Gram+ or Gram -.
E.Coli and Staph
Gram StainGram+ bacteria have simpler cell
walls with lots of peptidoglycan, and stain a dark purple color.
Anthrax
Gram StainGram- bacteria have more
complex cell walls with less peptidoglycan, thus absorb less of the purple dye used and stain a pinkish color insteadE.coliPseudomonus aerugenosa
Gram StainGram- bacteria often incorporate
toxic chemicals (called endotoxin) into their cell walls, thus tend to cause worse reactions in our bodies.
antibiotics like penicillin are less effective against gram negative bacteria.
Ampicillin was developed to treat gram negative bacteria
Gram StainGram staining involves a four-
part process, which includes:◦crystal violet, the primary stain◦ iodine, the mordant◦a decolorizer made of acetone and
alcohol◦safranin, the counterstain