Chapter #20 : Bacteria and Viruses I. Bacteria A. Classifying Prokaryotes Prokaryote – a single-celled organism that lacks a nucleus/major organelles. -All prokaryotes used to belong to the Kingdom Monera. -They’re now divided into 2 groups : 1. Kingdom Eubacteria – larger group that is found almost everywhere, ex : fresh water, salt water, land, inside our bodies (E.coli). -Cell walls of Eubacteria contain the carbohydrate peptidoglycan.

Kingdom Archaebacteria 2. Kingdom Archaebacteria - bacteria that live in harsh environments & are chemically different from Eubacteria. -Lack peptidoglycan & have different membrane lipids. *Archaebacteria have DNA sequences that are similar To Eukaryotic organisms (are thought to be ancestors of Eukaryotes).

3 Types of Archaebacteria : 1. Methanogens – prokaryotes that produce methane gas & live in oxygen-free environments, ex : human gut & thick mud in swamps. Aerobe – bacteria that require oxygen for survival. Anaerobe – bacteria that live in oxygen-free environments (oxygen is a poison to them). 2. Thermophiles – live in extremely hot environments : “therm” = heat, ex : hot springs & undersea vents. 3. Halophiles – live in extremely salty environments, ex : Salt Lake & the Dead Sea.

B. Identifying Prokaryotes *Prokaryotes are identified by : 1. Shape. 2. Chemical nature of their cell walls. 3. The way they move. 4. The way they obtain energy.

Shape - 3 basic bacterial shapes : A. Bacilli – rod-shaped prokaryotes. B. Cocci – spherical or circular prokaryotes. C. Spirilla – spiral or corkscrew- shaped prokaryotes.

Shape - 3 basic bacterial shapes : Other shapes : a. Strepto – chains of bacteria. b. Staphylo – grape-like clusters of bacteria. c. Diplo – 2 bacteria together. d. Mono – 1 bacterium.

Cell Walls - 2 Types in Eubacteria : *The method of Gram-staining is used to tell them apart. In Gram staining : 1. 2 dyes are applied to bacteria. a. Violet stain – primary stain. b. Red stain – counter stain. 2. Violet stain is applied first & stains peptidoglycan cell walls. 3. Alcohol is applied & if bacteria stay violet it is Gram-positive. 4. If bacteria are Gram-negative they have thin walls & an outer lipid layer. Alcohol dissolves lipids & counter stain dyes them red/pink.

Gram Staining Gram positive Gram negative

Movement – Structures used & types : Flagella – whip-like structures used for movement. Other ways to move : lash, snake, spiral forward, or glide along a layer of slime-like material they secrete.

Basic Bacterial Structure

Basic Bacterial Structure

Chloroplast

The Importance of Bacteria Bacteria impact living organisms on a daily basis. How are they good? How are they bad?