Classifying and Ordering Bacteria Help

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By — McGraw-Hill Professional
Updated on Aug 30, 2011

Introduction to Bacteria Characteristics and Classification

In this section the main emphasis will be on the characteristics of bacteria.

Gram Stain

Most of the prokaryotes (monerans or members of the Kingdom Monera) known about, today, are bacteria. Hence, we can nickname the bacteria as the “kings” of Monera! One relatively simple way of classifying bacteria is the way they react to particular biological dyes or stains, such as the iodine-rich Gram stain . Bacteria are classified as being gram-positive if they stain violet with the Gram stain. They are called gram-negative if they lose the violet and take the color of the red opposite stain.

Autotroph or Heterotroph

Another way of classifying bacteria and other monerans is by the general way in which they get their energy supplies. Recall that autotrophs are self-nourishing organisms, often relying upon photosynthesis for their ATP. And, likewise, remember that heterotrophs are nourished from some other source beyond themselves, usually by eating organic foodstuffs. Bacteria, too, can be classified as either autotrophs or as heterotrophs.

Autotroph Classifications

Among the autotrophs, there are two additional classifications, according to the specific way in which the bacteria are self-nourishing. Photoautotrophs ( FOH -to- aw -tuh- trohfs ) contain chlorophyll and use light and photosynthesis for their energy. Chemoautotrophs ( KEM -oh- aw -tuh- trohfs ) use chemical reactions, such as nitrogen-fixation , to produce their food. Nitrogen-fixing bacteria take nitrogen gas (N 2 ) out of the atmosphere and get energy by converting it into ammonia (NH 3 ) or ammonium (NH + 4 ). Nitrogen-containing organic compounds like these, once produced by chemoautotrophs, are then used by green plants for their own metabolism.

The Major Types Of Bacterial Shapes

In addition to classifying bacteria by the way in which they obtain their energy, they can also be slotted according to their shape (see Figure 6.3).

Coccus - Rounded Bacteria

A coccus ( COCK -us), or in plural form cocci ( COCK -see), is rounded and sphere-shaped, like a “berry.” A single berry-shaped bacterium is technically called a micrococcus ( MY -kroh- cock -us). Diplococci ( DIP -low- cock -see), in contrast, are “double berries.” The diplococci are a group of spherical bacteria that occur in pairs (hence, doubles). Strept ( STREPT ) means “twisted.” Hence, the streptococci ( STREP -toe- cock -see) are a genus of berry-shaped bacteria found as long twisted chains. Finally, consider the staphylococci ( STAF -ill-oh- cock -see). These rounded, berry-like bacteria assume the shape of a “bunch of grapes” (staphyl).

Bacillus - Rod Shaped

In contrast to the rounded coccus form are the bacillus (bah- SIL -us) or “rod” shape and the spirillum (spy- RIL -um) or “coil” shape. Similar to the coil shape taken by the spirilla (spy- RIL -uh) is the “coiled hair” arrangement assumed by the spirochetes ( SPY -row-keets).

Bacteria and the “Homeless” Viruses Classifying and Ordering Bacteria: The “Kings” of Monera The Major Types Of Bacterial Shapes

Fig. 6.3 Some major types of bacteria.


Practice problems for these concepts can be found at:  Bacteria and Viruses Test

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