Bacteria

• Bacteria differ from eukaryotes in at least seven ways.
• Bacteria are prokaryotes. Unlike eukaryotes, prokaryotes lack a cell nucleus.

Most bacterial cells are about 1 µm in diameter; most eukaryotic cells are more than 10 times that size.

• All bacteria are single cells.
• Bacterial chromosomes consist of a single circular piece of DNA. Eukaryotic chromosomes are linear pieces of DNA that are associated with proteins.
• Bacteria reproduce by binary fission, a process in which one cell pinches into two cells.
• Bacterial flagella are simple structures composed of a single fiber of protein that spins like a corkscrew to move the cell.
• Some bacteria also have shorter, thicker outgrowths called pili.
• Bacteria have many metabolic abilities that eukaryotes lack. For example, bacteria perform several different kinds of anaerobic and aerobic processes, while eukaryotes are mostly aerobic organisms.

Shape

• A bacterial cell is usually one of three basic shapes: bacillus, a rod-shaped cell; coccus, a round-shaped cell; or spirillum, a spiral cell.
• Members of the kingdom Eubacteria have a cell wall made of peptidoglycan, a network of polysaccharide molecules linked together with chains of amino acids.
• Outside the cell wall and membrane, many bacteria have a gel-like layer called a capsule.
• Eubacteria can have two types of cell walls, distinguished by a dye staining technique called the Gram stain.
• Gram staining is important in medicine because the two groups of eubacteria differ in their susceptibility to different antibiotics.
• Antibiotics are chemicals that interfere with life processes in bacteria.
• Some bacteria form thick-walled endospores around their chromosomes and a small bit of cytoplasm when they are exposed to harsh conditions.
• Pili enable bacteria to adhere to the surface of sources of nutrition, such as your skin. Some kinds of pili enable bacteria to exchange genetic material through a process called conjugation.
• Conjugation is a process in which two organisms exchange genetic material.

• Photosynthetic bacteria can be classified into four major groups based on the photosynthetic pigments they contain: purple nonsulfur bacteria, green sulfur bacteria, purple sulfur bacteria, and cyanobacteria.
• Green sulfur bacteria and purple sulfur bacteria grow in anaerobic environments.
• Cyanobacteria are thought to have made the Earth’s oxygen atmosphere.
• Bacteria called chemoautotrophs obtain energy by removing electrons from inorganic molecules such as ammonia and hydrogen sulfide or from organic molecules such as methane.
• In the presence of one of these hydrogen-rich chemicals, chemoautotrophic bacteria can manufacture all their own amino acids and proteins.

• Most bacteria are heterotrophs.
• Many are aerobic, that is, they live in the presence of oxygen. Some other bacteria can live without oxygen.
• Together with fungi, heterotrophic bacteria are the principal decomposers of the living world; they break down the bodies of dead organisms and make the nutrients available to other organisms.
• Heterotrophic bacteria obtain nutrients by secreting enzymes that break down complex organic structures in their environment and then absorbing them. If that environment is your throat or lungs, this can cause serious problems.
• Several common bacterial diseases include dental cavities, strep throat, tuberculosis, and acne.

• The second way bacteria cause disease is by secreting chemical compounds into their environment. These chemicals, called toxins, are poisonous to eukaryotic cells.
• When bacteria grow in food and produce toxins, the toxins can cause illness in humans who eat those contaminated foods.
• Most bacteria can be killed by boiling water or various chemicals.

• In 1928, the British bacteriologist Alexander Fleming discovered the antibiotic penicillin.
• Today different antibiotics are used to interfere with different cellular processes.
• Because these processes do not occur in viruses, antibiotics are not effective against them.
• Some bacteria have become resistant to antibiotics.
• Susceptible bacteria are eliminated from the population, and resistant bacteria survive and reproduce, thus passing on their resistance traits.
• Usually, if the full course of the antibiotic is administered, all the targeted bacteria are killed and there is no chance for a resistant strain to develop. If antibiotic treatment ends prematurely, some of the more-resistant bacteria may survive and reproduce.

Mining and Environmental Uses of Bacteria

• Mining companies can use bacteria to concentrate desired elements from low-grade ore.
• Bacteria metabolize different organic chemicals and are therefore used to help clean up environmental disasters such as petroleum and chemical spills.
• Powders containing petroleum-metabolizing bacteria are used to help clean oil spills.