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. They are able to sense the presence of certain nutrients in their environment and move toward them and they are able to move away from harmful substances.Milk-curdling Lactobacillus acidophilus are bacilli bacteria, meaning they are cylindrical-shaped. Using flagella, bacteria are able to respond to environmental stimuli.
Bacteria can have multiple flagella that surround the cell, a few flagella on one or both ends of the cell, or a single flagella. These structures move in a circular motion to propel the bacteria forward. Some, but not all, bacteria have one or more flagella. Because it has no cell wall it can have a variety of shapes.ģ) flagella –a whip-like structure used for movement. Mycoplasma pneumoniae is an example of a cell wall-less bacteria. They have, instead, chemical compounds which protect the bacteria against drying out and they usually live in environments in which osmotic pressures are not a problem for survival. coli (stained pink).Ī few bacteria do not have cell walls. The image at the left as seen through a microscope shows both Gram-positive (stained dark purple) rod-shaped bacteria, Bacillus cereus, and the smaller Gram-negative rod-shaped bacteria E.
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