Bacteria An Overview

Bacteria Bacteria is the plural of bacterium Prokaryotic cells – no true nucleus Have one double stranded chromosome May have additional DNA called a plasmid Reproduce by binary fission Most are benign Some are pathogenic

Kingdoms Two kingdoms include prokaryotic cells Archaebacteria ◦ Extremophiles ◦ Methanogens - intestines ◦ Halophiles - salt ◦ Thermophiles – heat tolerance ◦ May have been on Earth for 3.5 billion years Eubacteria – all other bacteria

Archeabacteria Thermophile 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 Bacteris Yellowstone Thermophile mats Grand 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 Eubacteria Bacteria can be characterized by shape

Characterizing Bacteria Bacteria is also classified by their oxygen requirements Aerobic Bacteria require oxygen to support reproduction ◦ Esherichia coli Anaerobic bacteria reproduce in the absence of oxygen ◦ Listeria ◦ Clostridium botulinum

Characterizing Bacteria Facultative bacteria reproduce either in the presence or in the absence of oxygen. ◦ Salmonella ◦ Staphylococcus aureus ◦ Bacillus cereus

Characterizing Bacteria Bacteria secrete a covering for themselves - cell wall Do not contain cellulose like plant cell walls Mostly 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 Bacteria Some 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 Bacteria Dr. 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 Stain the 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 Stain Gram + bacteria have simpler cell walls with lots of peptidoglycan, and stain a dark purple color. Anthrax

Gram Stain Gram - bacteria have more complex cell walls with less peptidoglycan, thus absorb less of the purple dye used and stain a pinkish color instead E.coliPseudomonus aerugenosa

Gram Stain Gram - 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 Stain Gram 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