Submitted by-Debashish Dey- 31330092

Morphology of Bacteria & Its Characteristics

MorphologyOne-celled organisms that can range from 0.5 to over 100 micrometers in size are called bacteria. Bacteria can be complex despite their small size and lack of a nucleus. Bacterial classification is based primarily on their shape. The three most common bacterial shapes are the round or oval coccus, the rod-shaped bacillus and bacteria with a spiral shape spirillum.Bacteria are classified by direct examination with the light microscope through its morphology and aggregation.

CoccusA coccus (plural cocci, from the Latin coccinus

(scarlet) and derived from the Greek kokkos (berry) is any microorganism  (usually bacteria) whose overall shape is spherical or nearly spherical. 

AggregationsAggregations of coccoid bacteria often occur and these

forms have specific names as well; listed here are the basic forms as well as representative bacterial genera:

pairs, or diplococci (Neisseria)groups of four or eight known as tetrads or sarcina (

Micrococci)bead-like chains, or streptococci (Streptococcus)grapelike clusters, or staphylococci (Staphylococcus)

DiplococcusA diplococcus (plural diplococci) is a round bacterium (a coccus) that typically occurs in pairs of two joined cells. Examples are Streptococcus pneumoniae, Moraxella catarrhalis

SarcinaSarcina is a genus of  cocci bacteria. They have a cuboidal cell arrangement i.e eight cells joined together in the form of a cuboid. Examples Sarcina ventriculi

Tetrads The tetrad occurs in a subgroup of the cocci where the bacterium divides in two planes to form a  square of four bacteria called a tetrad. Examples of tetrad-forming bacteria are the lactic acid bacilli, Aerococcus.

Streptococcus Streptococcus is a genus of coccus (spherical) belonging to the phylum Firmicutes and the Lactobacillales (lactic acid bacteria) order. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs. Examples S. pneumoniae ,S. canis , etc.

StaphylococcusStaphylococcus (from the Greek: staphylē, "grape"  kókkos, "granule") is a genus of Gram-positive bacteria. Under the microscope, they appear round (cocci), and form in grape-like clusters. Examples are S. agnetis , S. aureus , etc.

BacillusBacillus is a genus of Gram-positive, rod-shaped (bacillus), bacteria and a member of the phylum Firmicutes.  Bacillus species can be obligate aerobes (oxygen reliant), or facultative anaerobes (having the ability to be aerobic or anaerobic). Examples are B.subtilis , B. anthracis etc.

SpirillumSpirillum is a genus of Gram-negative bacteria within family Spirillaceae. Spiral bacteria can be sub-classified as spirilla, spirochetes, or vibrios based on the number of twists per cell, cell thickness, cell flexibility, and motility. Members of Spirillum are large, elongate, spiral shaped, rigid cells. Some have tufts of flagella at both poles. They are usually found in stagnant freshwater rich in organic matter.

CharacteristicsRespiration in bacteria: Anaerobic bacteria: does not require oxygen for

respiration.Aerobic bacteria: require oxygen for respiration.

Gram staining bacteria are a method of differentiating bacterial species into two large groups, which are based on their chemical and physical properties of their cell wall.

Gram positive bacteria: Those bacteria when they are stained in gram stain results in purple colour.

Gram negative bacteria: Those bacteria when they are stained in gram stain results in pink colour.

Locomotion of bacteria:They move around by using their locomotion organs such as cilia and flagella.

Nutrition of bacteria: They exhibits different modes of nutrition level such as-

Autotrophic bacteria: These bacteria are able to synthesize their own food. For e.g.: Phototropic bacteria and chemosynthetic bacteria

Heterotrophic bacteria: These bacteria are unable to synthesize their own food, hence they depends on other organic materials. For e.g.: saprophytic bacteria-these bacteria feeds on dead and decaying matter.

Symbiotic bacteria: These bacteria have a mutual benefit from other organisms. For e.g.: nitrogen fixing bacteria (or) rhizobium. 

Parasitic bacteria: These bacteria are present in plants, animals and human beings. These bacteria feeds on host cells and causes harm to the host. 

Reproduction in Bacteria: The reproduction in bacteria is mainly by cell division and binary fission. In some cases few bacteria also reproduce by budding.