Chapter 7 Kingdoms Bacteria andArchaea

Chapter 7 : Kingdoms Bacteria and Archaea. Bacteria have prokaryotic cells, usually 1 - 5 micrometers wide. Many species are mutualistic eg bacteria in gut of herbivores. Most bacteria are not harmful. In fact, normal bacteria on the skin keep the skin healthy. Reproduction in bacteria 1) Binary fission - one cell splits in two ( asexual ). 2) Conjugation - sex pili are used to transfer genes from one bacteria to another. 3) Transduction - viruses accidentally move genetic material from one bacteria to another. Bacteria are classified by : a) shape of cells Fig 17.4. Images of bacteria round : coccus eg Streptococcus mutans rod shape : bacillus eg Bacillus thuringiensis (Bt used as insecticide) Escherichia coli ( E. coli ) spiral : spirillum eg Treponema pallidum (causes syphilis) b) Gram stain You stain the bacteria first with violet dye, then a red dye. Bacteria with peptidoglycan on the outside of the cell wall stain violet (Gram positive) eg Streptococcus. Bacteria with cell membrane on the outside stain red (Gram negative) eg Escherichia. Many antibiotics prevent bacteria from producing peptidoglycan eg Penicillin. Antibiotics are often given to farm animals, which increases the risk of antibiotic resistant bacteria infecting humans. Types of bacteria 1) Kingdom Archaebacteria - ancient, fossils 3.5 billion years old - usually obligate anaerobes. - have no peptidoglycan and no flagella - are divided into three main groups : a) Methanogens - produce methane gas - found in swamps, sewage treatmentplants, animal intestines; decomposers eg Methanosarcina b) Halophiles - live in very salty water ; autotrophs. They grow best at 35 - 50 oC. eg Halobacterium c) Thermophiles - live in hot springs. They grow best at 70 - 100 oC. - eg Pyrococcus and Thermus (used in Polymerase Chain Reaction) 2) Kingdom bacteria - more modern, have peptidoglycan. - often form resistant endospores. - may have flagella for movement There are many groups, including : a) Cyanobacteria ( blue/green algae ); autotrophs, they were the first organisms that produced oxygen in the atmosphere. - eg Anabaena b) Enteric bacteria - live in the digestive system. - eg Escherichia - many are useful eg Lactobacillus, which helps digestion and reduces cancer risk in humans. c) Nitrogen fixing bacteria - in soil and legumes. They convert nitrogen gas in the air to ammonia or nitrate eg Rhizobium Bacteria are used in bioremediation - removing toxic chemicals from soils. Other bacteria are used in manufacturing chemicals such as citric acid, human proteins (insulin, growth hormone), anti-cancer drugs, and also in biotechnology to produce genetically modified (GM) crops. Energy use and Organic molecules Chemoheterotrophs : take in organic molecules and use them for energy - eg bacteria, fungi, animals Chemoautotrophs : take in carbon dioxide and make organic molecules using energy from inorganic compounds - eg bacteria Photoautotrophs : take in carbon dioxide, and use light for energy - eg green plants, bacteria Photoheterotrophs : take in organic molecules, and use light for energy - eg bacteria