KINGDOM MONERA The Prokaryotes Archaebacteria and Eubacteria BY

KINGDOM MONERA The Prokaryotes: Archaebacteria and Eubacteria BY : ASRURI R. ASY-SYIFA

i. Characteristics of Bacteria Prokaryote means “before a nucleus. ” They are single-celled organisms and the smallest, simplest organisms. This kingdom is subdivided into two kingdoms: Archaebacteria- Found in anaerobic conditions with high salt concentrations, high temperatures and a low p. H. These are believed to be the conditions on the primitive Earth’s early atmosphere didn’t contain oxygen. (anaerobic) Scientists believe that all life kingdoms are descended from this group. Archabacteria’s phyla are based on their habitats. Anaerobic Methanogens- live in the gut of animals, swamps and marshes and produce all of the methane gas found in the Earth’s atmosphere.

Halophiles- “salt-lovers” found in salt lakes such as the Dead Sea. Thermophiles – inhabit hot, acidic environments such as hot springs. ii. Eubacteria – This group includes the traditional bacteria and is the largest and most successful of the two kingdoms. Eubacteria species have allowed scientists to separate them into six phyla.

Bacteria are the oldest and most abundant organisms living on the Earth. (i. e. 10 m. L of soil contains 1 bacteria. They are found in nearly every habitat studied, including habitats that no other organisms are able to withstand. Bacteria all share these five characteristics -All bacteria are single-celled -All bacteria are prokaryotes. Their DNA is not surrounded by a membrane. -Cell organelles in bacteria are not surrounded by membranes. -The DNA of bacteria is made of a single chromosome. -All bacteria reproduce asexually by binary fission.

Structure of a Bacteria are the smallest organisms measuring from 1 -10 micrometres. It contains a cell wall that provides support and protection for the contents of the cell. The cytoplasm contains ribosomes, responsible for the formation of proteins and DNA. The DNA forms a single chromosome and forms a ring rather than a strand. Some bacteria have a whip-like flagella that act like propellers moving the organism forward. Some are also covered by a slime capsule. Bacteria are classified by their shape, reaction to being stained, nutrition and respiration.

Bacterial Cell Shape Bacteria can be classified by shape. -A spherical cell is called a coccus (pl. cocci) -A rod-shaped cell is called a bacillus (pl. bacilli) -A spiral-shaped cell is called a spirillum (pl. spirilla)

Cocci living as separate cells are called monococci, pairs are called diplococci, chains are called streptococci, and grapelike clusters are called staphlococci. Bacilli also exist as single cells, pairs (diplobacilli), or chains (streptobacilli). Spiral bacteria exist only as single cells. Staining bacteria results in two forms: grampositive (purple) vs. gram negative (pink).

Nutrition means obtaining energy and a source of carbon to produce the organic compounds needed for cellular metabolism. Most eubacteria are heterotrophs and obtain energy by breaking down organic molecules from their environment. Some are parasites, absorbing nutrients from living organisms. Others are saprobes, decomposing dead organic matter. Some eubacteria are autotrophs and produce their own organic compounds. (example- cyanobacteria (blue-green bacteria) are photoautotrophs using light for energy, but they lack true chloroplasts. Mode of nutrition Energy Source Carbon Source Photoautotroph Light Carbon Dioxide Chemoautotroph Inorganic Chemicals Carbon Dioxide Photoheterotroph Light Organic Compounds Chemoheterotroph Organic Compounds

Respiration Chemical reactions take place on the inner surface of the cell membrane so that gases can pass into and out of cells easily. All living things must carry out cellular respiration to receive energy. Bacteria differ in whether or not they require oxygen. If respiration requires oxygen, bacteria are termed aerobes. If oxygen is absolutely necessary for survival they are called obligate aerobes. Bacteria that carry out respiration without oxygen are called anaerobes. Presence of oxygen kills some bacteria and these are called obligate anaerobes. (example- Clostridium botulinum produces toxins that can cause an extreme form of food poisoning called botulism. ) Another group of bacteria can survive with or without oxygen and they are called facultative anaerobes.

Reproduction Bacteria reproduce asexually and divide by the process of binary fission. In binary fission, the parent cell divides into two offspring cells that are completely identical. There is no exchange of genetic material so the process is asexual. (example- E. coli produces between 10 and 100 million bacteria in 12 hours. )

When conditions begin to fail, either through decrease of food or space, or cooler temperatures, some bacteria take part in a type of sexual reproduction called conjugation. In conjugation the two cells join briefly and one cell donates some DNA (called plasmid) to the other one. Sexual reproduction combines genetic information from two different individuals and increases variation. Ex. - Antibiotic resistance in the 1950’s.

When growth conditions become extremely unfavourable, many gram positive bacteria form structures called endospores. Endospores are DNA and a small amount of cytoplasm enclosed in a tough cell wall. They are resistant to extremes in temperature, drying, and harsh chemicals.

The pros and cons of Bacteria convert atmospheric nitrogen into a useable form of nitrogen. (nitrogen-fixers) Bacteria play an important role in recycling by breaking down dead and decaying organic matter. Used to eliminate or neutralize toxic and hazardous waste and spills. Also used in sewage treatment to decompose the 5 billion kg of solid waste produced daily. Bacteria is used to produce dairy foods that help maintain a healthy balance of microorganisms in the digestive system. Only a small percentage of prokaryotes are pathogenic, or disease causing. These bacteria produce deadly toxins in the human body that cause disease symptoms. Endotoxins are seldom fatal and cause fever, vomiting and diarrhea. E. coli, Salmonella. Exotoxins are highly toxic, do not cause a fever and are often fatal. Tetanus and botulism. Example- Toxins released by the bacterium Streptococcus pneumoniae may result in symptoms of pneumonia.