Survey of Microorganisms - ppt download

Are Viruses Microorganisms

Virus / August 18, 2017

Bacteria, Protists, & VirusesWhat are Bacteria?

You can run, but you can't hide when it comes to bacteria. They can be found everywhere on earth, from Antarctica to the inside of your intestines! Some are good, aiding digestion and giving us tasty food like cheeses and yogurt. Many are harmful, causing serious diseases; these are called pathogenic bacteria. But what are bacteria?

Bacteria (or bacterium if you're speaking of only one) are one-celled or unicellular microorganisms that don't have chlorophyll and don't have a distinct membrane-enclosed cell nucleus, like plant and animal cells do. Instead, the nuclear material-a single strand of DNA-is folded and clumped in the interior of the cell. Microorganisms that don't have a distinct nuclear membrane are called prokaryotic organisms. Bacteria are classified in the kingdom Monera.

How are individual bacteria classified within the main kingdom? Scientists divide bacteria by shape: sphere, rod, and spiral. Spherical (round) bacteria include streptococcus, the cause of strep throat. Rod-shaped bacillus bacteria include anthrax and tetanus. Spiral bacteria have long bodies with a twist that form a spiral pattern when they are connected together; this group includes cholera.

Bacteria reproduce most commonly by binary fission where a single parent bacterium divides to form two independent bacteria. This type of reproduction is called asexual because there is no exchange or combination of nuclear material between two organisms. Fission occurs rapidly in as little as 20 minutes. Under perfect conditions a single bacterium could grow into over one billion bacteria in only 10 hours! A large group of bacteria is called a colony, which you can often see without magnification. Different colonies can be identified by their shape, texture, and color.

Some bacteria can also reproduce asexually by forming thick-walled endospores that are very resistant to conditions of extended heat, cold, or dryness. An endospore is formed within the cell body of a bacterium. Usually a bacterium forms only one endospore and that endospore will produce only a single bacterium. Endospores are difficult to kill except by strong chemicals or high heat. All the species in the Bacillus genus of bacteria produce endospores.