Major characteristics of microorganisms

Major characters of microorganisms

The major characteristics of microorganisms fall into the following categories:

1. Morphological characteristics:The cell shape, size, and structure; cell arrangement; the possession of special structure and developmental types; The staining reactions; and the motility and flagellar arrangement.
2. Chemical composition: The various chemical constituents of the cells.
3. Cultural characteristics: Nutritional requirement and physical conditions required for growth, and the manner in which growth occurs.
4. Metabolic characteristics: The way in which cells obtain and use the energy, carry out chemical reactions, and regulate these reactions.
5. Antigenic characteristics: Special large chemical components (antigens) of the cell, distinctive for certain kinds of microorganisms.
6. Genetic characteristics: characteristics of the hereditary material of the cell (deoxyribonucleic acid, or DNA) and occurrence and function of other kinds of DNA that may be present, such as plasmids.
7. Pathogenicity: The potential to cause disease in various plants or animals or even other microorganisms.
8. Ecological characteristics: Habitat and the distribution of the organism in nature and the interactions between and among species in natural environments.

Morphological characteristics

Different from other kinds of microbial characteristics, determination of morphological habits usually requires studying individual cells of a pure culture. Microorganisms are very minute and their size is usually expressed in micrometers (). One is equivalent to 0.001 millimeters (mm) or about 0.00004 in; consequently, periodic exam of microbial cells requires the use of a high-power microscope, usually at a magnification of about 1,000 diameters.

The involvement of electron microscopy gives a magnification of thousands of diameters and had making it possible to see fine structure of cell structure. Various techniques are available for the microscopic examination of microorganisms. The technique selected depends on upon the information which is being searched.

Chemical characteristics

Microbial cells consist of a large variety of organic compounds. When cells are torned apart and their components subjected to chemical analysis, each and every kind of microorganism is found to have a characteristics chemical composition. Both qualitative and qualitative difference in composition occur among various species. For example, the occurrence of lipopolysaccharide in cell walls is characteristic of gram-negative bacteria but nor gram-positive bacteria; on the other hand, many gram-positive bacteria have cell walls that contain teichoic acids, compounds are not found in gram-negative bacteria. Fungal and algal cell walls are different in composition from those of bacteria. A important distinction among viruses is made on the basis of the kind of nucleic acid they possess, namely ribonucleic acid (RNA) or deoxyribonucleic acid (DNA).

Cultural characteristics

Each kind of microorganisms has definite growth requirements. Many microorganisms can be grown in or on a culture media (a mixture of nutrients used in the laboratory to support growth and multiplication of microorganisms). Few microorganisms can grow in a medium containing only inorganic compounds, whereas some may require a medium containing organic compounds (amino acid, sugars, purines or pyrimidines, vitamins, or coenzymes). Some require complex natural substances (peptone, yeast autolysate, blood cells, or blood serum), and some cannot as yet be cultured in an artificial laboratory medium and can be propagated only in a living host or living cells. For example, rickettsias require a host in which to grow, such as an animal, a fertilized chicken egg (chick embryo), an arthropod, or a culture of mammalian tissue cells. The host functions as a very complex “medium” for such nutritionally demanding microorganisms.

In addition to specific nutrients, every kind of organism also requires specific physical conditions for growth. For example, some bacteria grow best at high temperatures as thermophiles and cannot grow below 40; others grow best in cold and cannot grow above 20; still, others, such as bacteria pathogenic to humans, needs a temperature close to that of the human body (i.e., 37). The gaseous atmospheric environment required for growth is also important; for instance, some bacteria require oxygen for growth; oxygen is lethal n harms to others and they can grow only in its absence. Light may be another essential physical condition; certain bacteria, such as cyanobacteria, require light as a source of energy, whereas others may be okay to light or may even find it deleterious to their deevelopment.

Every type of microorganism grows in a characteristics manner. For example, growth in a liquid medium may be abundant or sparse; it may be evenly dispersed throughout the medium, or it may occur only as a segment at the bottom or only as a thin film or pellicle at the top. On solid media, microbes grow as colonies-distinct, compact masses of cells that are macroscopically visible. Colonies are characterized by their size, shape, texture, consistency, color and other notable characteristics.

Metabolic characteristics

The life processes of the microbial cell are a complex integrated series of chemical reactions collectively referred to as metabolism. The variety of these reactions affords many opportunities to characterize and differentiate various groups of microorganisms. For instance, some organisms may gain energy by absorbing light, others by oxidizing various organic or inorganic compound, and others by redistributing the atoms within certain molecules so that the molecules become less stable and reactive . Organisms also differ in the ways in which they synthesize their cell components during development. The various chemical reactions of an organism are catalyzed by proteins are called enzymes, and the complement of enzymes possessed by one kind by an organism, as well as the ways in which those enzymes are regulated, can differ significantly from that of other organisms.

Antigenic characteristics

Certain chemical compounds of microbial cells are called antigens. Antigenic ability of a microorganism has great practical importance. If microbial cells went inside the animal body, the animal responds to their antigens by forming specific blood serum proteins called antibodies, which binds to the antigens. Antibodies are highly used as tools for the rapid identification of particular kinds of microorganisms.

For the present thus might be explained as “lock and key system”. Because of the highly specific nature of the reaction, if we know the character of one part of the system (antigen or antibody) we can identify the other. For example, if we take typhoid bacterium antibody and mixed it with a suspension of unknown bacterial cells, and a positive reaction occurs, we can decide that the cells are those of the typhoid organism. If no reaction occurs, then these bacterial cells are of some other species other than the typhoid bacterium.

Genetic characteristics

The double-stranded chromosomal DNA of every type of microorganisms has certain features that are constant and characteristics for that organism and useful for its classification:

1. DNA base composition: it is essential to note that the DNA molecule is made up of base pairs; guanine-cytosine and adenine-thymine. Of the total number of nucleotide bases found in DNA, that percentage represented by guanine plus cytosine is termed the moles % G+C value (or more briefly, mol% G+C).Values for various organisms range from 23 to 75.
2. The sequence of nucleotide bases in the DNA: This sequence is not common for reach kind of organism and is the most fundamental of all the characteristics of an organism: it has the great significance of microbial classification.

More than to chromosomal DNA, plasmid DNA may sometimes be present in microbial cells. plasmids are circular DNA molecules that are capable of autonomous replication within bacterial cells, and their activity can confer special characteristics on the cells that contain them, such as the ability to make toxins (toxigenicity), to become resistant to various antibiotics, or to use unusual chemical compounds as nutrients.

Pathogenicity

The tendency to cause disease, or pathogenicity, of some microorganisms, is surely a dramatic nature and it stimulated much of the early work with microorganisms. Although we are known that relatively few species of microorganisms cause disease, Some of microorganisms are pathogenic for animals or plants, and some microorganisms may cause disease in other microorganisms.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.