Conjunction happens when bacteria make direct contact. Transduction occurs when a virus picks up DNA from one bacterium and infects another bacterium, inserting the new gene sequence. In these circumstances, it might be evolutionarily advantageous to try out some new DNA. This usually happens when nutrients are scarce or when the density of a bacterial colony is high. (The DNA fragments are released into the environment by other bacteria.) To undergo transformation, a bacterium must be in a state known as competence. Transformation is the most common process of horizontal gene transfer and occurs when a bacterium absorbs short DNA fragments from the environment through its cell membrane. This diagram of shows the stages of bacterial conjugation. There are three ways horizontal gene transfer occurs: transformation, transduction and conjugation. The resulting genetic variation ensures that bacteria can adapt and survive as their environment changes, Live Science previously reported. This is known as horizontal gene transfer, according to the San Diego State University College of Sciences. Therefore, bacterial cells introduce variation into their genetic material by integrating additional DNA, often from their surroundings, into their genome. It starts off as a small nub, grows until it is the same size as its parent and then splits off.Īfter binary fission or budding, the DNA found in parents and offspring is exactly the same. In this case, the daughter cell grows as an offshoot of the parent. Some types of bacteria, such as cyanobacteria and firmicutes, reproduce via budding. The cell then splits apart, pushing the duplicated material out and creating two identical "daughter" cells. In this process, a single bacterial cell, called the "parent," makes a copy of its DNA and grows larger by doubling its cellular content. Most bacteria multiply by a process called binary fission, according to the Cornell University College of Agriculture and Life Sciences. Some enter symbiotic, or mutually beneficial, relationships with a host (more on this later). Some bacteria are photosynthetic, while others are master decomposers, breaking down rotting and decaying organic material into nutrients. How do bacteria eat and reproduce?Īs some of the oldest life-forms on Earth, bacteria have evolved a dizzying number of ways to survive. These chromatophores hold pigments used in photosynthesis. Photosynthetic bacteria, which generate energy from sunlight, may have structures called chromatophores spread throughout their cytoplasm. The cytoplasm of some bacteria may also have little pockets, called inclusions, where nutrients are stored for lean times. Some antibiotics, like tetracycline, target bacterial ribosomes to prevent them from synthesizing proteins, thus dooming the cell. Within the cytoplasm float the nucleoid, plasmids and tiny protein factories called ribosomes, which are the sites where the cell's genetic instructions are translated into the cell's products. pneumoniae is a Gram-positive bacterium, but Escherichia coli, which can cause food poisoning, and Vibrio cholerae, which causes cholera, are Gram-negative bacteria.ĭelving beneath the cell wall and membrane, bacteria contain cytoplasm, a solution of mostly water and salts. Gram-negative bacteria, which do have an outer membrane, don't pick up the stain. The test stains Gram-positive bacteria, or bacteria that do not have an outer membrane. Whip-like extensions often cover the surfaces of bacteria - long ones, called flagella, or short ones, called pili - and help bacteria move around and attach to a host.īacteria can be classified by the composition of their cell walls using a test called the Gram stain, according to the Science Education Resource Center at Carleton College. Some bacteria may even have a third, outermost protective layer, called the capsule. Certain bacteria, like the mycoplasmas, do not have a cell wall at all. For example, the milk-curdling Lactobacillus acidophilus are bacilli, and pneumonia-causing Streptococcus pneumoniae are a chain of cocci.īacterial cells are generally surrounded by an outer cell wall and an inner cell membrane. The shapes and configurations of bacteria are often reflected in their names. The scientific names for these shapes are cocci (round), bacilli (cylindrical), vibrios (comma-shaped), spirochaetes (corkscrew) and spirilla (spiral). (Image credit: Shutterstock)īacteria come in five basic shapes: spherical, cylindrical, comma-shaped, corkscrew and spiral. Milk-curdling Lactobacillus acidophilus are bacilli bacteria, meaning they are cylindrical-shaped.
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