Biodiversity Prokaryotes

Prokaryotes are the most numerous living organisms (the number of cells in a handful of fertile soil is greater than the number of humans who have ever existed on Earth). They are almost ubiquitous (found almost everywhere) including some of the harshest environments on Earth. Why are they so successful?

structures such as cell walls made of peptidoglycan (a glycoprotein unique to prokaryotes) that maintain cell shape, provide protections and prevent lysis in hypotonic environments,

a capsule that protects cells from dehydration, protects the cells from chemicals of the immune systems of hosts, and also helps the cell attach to surfaces or other cells.

many prokaryotes are capable of motility mostly by flagella

mutate rapidly periods of exponential population growth (reproduce by binary fission) a great deal of genetic diversity Gene transfer

Transformation

Transduction

Conjugation

Some species produce endospores that allow the cell to remain dormant when conditions are not favorable for survival.

Typical structure of a bacillus with a polar monotrichous flagellum

The existence of all life is dependent on these organisms All life on the planet evolved from ancestral bacteria. 2. The early bacteria “prepared” the environment for future species. 3. Due to their functions in the ecosystems, all life would cease to exist if they were eradicated

Some bacteria are important tools in genetic engineering.

Morphology Bacteria may exist as single cells, or they may be filamentous or colonial.

The three most common shapes of bacteria are: coccus (plural cocci), bacillus (plural bacilli), spirillus (plural spirilla)

Most bacteria have cell walls Most bacteria have cell walls. The cell walls of the eubacteria are composed of peptidoglycan, but the chemical composition is different from the archeabacteria.

See table in notes for differences in the members of the three domains

Genome 1. Bacteria possess about 1/1,000 as much DNA as eukaryotes. 2. The DNA is concentrated in a nucleoid; it is circular, and double-stranded.

Metabolic Diversity 1. photoautotrophs utilize light energy and CO2 (e.g., the cyanobacteria) 2. photoheterotrophs utilize light and carbon in an organic form (restricted to some prokaryotes) 3. chemoautotrophs utilize CO2 and energy from the oxidation of inorganic substances (also called chemosynthetic autotrophs, only in prokaryotes) 4. chemoheterotrophs obtain energy from organic compounds (the majority of the bacteria do this).

Cyanobacteria

Photoheterotrophs

Chemoautotrophic whale-fall community, including bacteria mats Chemoautotrophic whale-fall community, including bacteria mats. (HR) http://images.google.com/imgres?imgurl=http://oceanexplorer.noaa.gov/explorations/06mexico/logs/may16/media/whalefall_100.jpg&imgrefurl=http://oceanexplorer.noaa.gov/explorations/06mexico/logs/photolog/photolog.html&h=75&w=100&sz=3&hl=en&start=29&usg=__GV0RbkCn6ANV6tCFT7KATDj7zqg=&tbnid=jeNbNV_G425rfM:&tbnh=62&tbnw=82&prev=/images%3Fq%3Dchemoautotrophs%2Bpurple%2Bbacteria%26start%3D20%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN

Chemoheterotrophs

Domain Archaea. The oldest living organisms. The extant species are found in extreme environments. Unique in that they do not have peptidoglycan, and have cell membranes that are different from those of other living organisms Taxa include methanogens, thermophiles, and halophiles.

Thermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park

Methanogens

Domain Bacteria includes many taxa such as:

Gram positive bacteria (cocci and bacilli)

The streptococci are those that are arranged in chains and sometimes in pairs.

The staphylococci are arranged in clusters The staphylococci are arranged in clusters. They are faculatively anaerobic and catalase positive. A medically important species is Staphylococcus aureus (sepsis, Toxic Shock Syndrome etc.).

The clostridia are spore formers, Gram positive, and bacilli The clostridia are spore formers, Gram positive, and bacilli. They are strict anaerobes often found in soil and are responsible for some serious diseases such as gangrene (Clostridium perfringens), botulism (C. botulinum), and tetanus (C. tetani).

Lactic Acid Bacteria are Gram positive organisms that produce lactic acid as an end product of fermentation. These catalase negative organisms include the lactobacilli are non-spore formers that are found in the mouth and the vagina.

The members of the genus Bacillus are also spore formers that include free-living forms as well as the bacterium that causes anthrax (B. anthracis).

The spirochetes (spirally shaped bacteria) are unique in that they have a flexible cell wall and axial filaments (for motility).

Chlamydias are unique in that they lack peptidoglycan and there are two forms in their life cycle.

Cyanobacteria are photosynthetic autotrophs that are abundant in marine and fresh water ecosystems.

Proteobacteria are Gram negative species that are classified within subgroups. Some of these are beneficial such as nitrogen fixing symbiotic species. Others are harmful such as Rickettsia rickettsia that causes Rocky Mountain Spotted Fever.

Rickettsia rickettsia

Important Evolutionary Trends: single cells to filamentous forms, community interactions among different species and compartmentalization of functions within cells leading to the formation of eukaryotic cells.