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What is Bacteria? What are Bacteria?

written by: •edited by: Paul Arnold•updated: 8/18/2009

What is bacteria? This is one of the most frequently asked questions about microbes. Bacteria is plural, bacterium is singular so the question should be phrased - what is a bacterium? or what are bacteria? In this article we will look at some of the most fascinating types of bacteria.

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    Bacteria Types

    Bacteria are prokaryotic cells and are neither plants nor animals. They are tiny living single-celled microorganisms that range in size from a few micrometres to several centimetres in length, and they can be found in every habitat on Earth. They are probably the planet's most successful colonizers and can exist in every type of niche, from the depths of the ocean to the tops of mountains. They can grow in acidic, and radioactive environments as well as making their homes in other organisms such as plants and humans.

    A gram of soil will typically contain 40 million bacterial cells and they make up much of the biomass of the planet. There are three main types of bacteria:

    • Spherical - are known as cocci (singular) or coccus (plural)
    • Spiral - are known as spirilla (singular) or spirillus (plural). Tightly coiled forms are called spirochaetes.
    • Rod shaped - are known as bacilli (singular) bacillus (plural). Some rod shaped bacteria, called vibrio, are slightly curved, like a comma.

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    Examples of Bacteria

    The bacterial world is full of fascinating organisms, some are harmful, and others are benign and even beneficial. Here are just a few examples:

    Flesh eating bacteria - they don't actually eat flesh, but the toxins they release dissolve skin and the fascia connective tissue that covers muscles. The condition is known as necrotizing fasciitis and it is rare. Several types of bacteria can cause the disease, but the most common flesh eating bugs belong to group A streptococcal bacteria, particularlyStreptococcus pyogenes.

    Bacterial toxins - toxins released by other types of bacteria can also be extremely harmful, and cause illnesses such as diphtheria, botulism, and tetanus. Diphtheria is caused by Corynebacterium diphtheriae, botulism is caused by Clostridium botulinum, and tetanus is caused by Clostridium tetani.

    Friendly bacteria - then there are the friendly types that live on and inside you, but don't cause you any harm. In fact they are very beneficial and good to have around. Bifidobacterium longum lives in the human digestive tract and helps to keep the entire digestive process functioning smoothly. Lactobacillus salivarus makes a nice home inside your mouth, and produces lactic acid which can prevent the growth of pathogenic bacteria.

    Ice-minus bacteria - these coolly named microbes are mutant strains of the common wild-type bacteria Pseudomonas syringae. They are sprayed on crops to prevent frost from forming.

    E.coli and E. coli DNA - this is probably the most studied organism in biology. It's found in the lower intestines of mammals and has helped in many areas of scientific research including the development of DNA sequencing technology. Only a small handful of E.coli strains are harmful