Bacteria

 

Bacteria are single celled microbes. The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles. Instead their control centre containing the genetic information is contained in a single loop of DNA. Some bacteria have an extra circle of genetic material called a plasmid. The plasmid often contains genes that give the bacterium some advantage over other bacteria. For example it may contain a gene that makes the bacterium resistant to a certain antibiotic.

Classification of Bacteria

Until recently classification has done on the basis of such traits as:

• shape
  • bacilli: rod-shaped
  • cocci: spherical
  • spirilla: curved walls
• ability to form spores
• method of energy production (glycolysis for anaerobes, cellular respiration for aerobes)
• nutritional requirements
• reaction to the Gram stain. 

  

 Bacteria are found in every habitat on Earth: soil, rock, oceans and even arctic snow. Some live in or on other organisms including plants and animals including humans. There are approximately 10 times as many bacterial cells as human cells in the human body. A lot of these bacterial cells are found lining the digestive system. Some bacteria live in the soil or on dead plant matter where they play an important role in the cycling of nutrients. Some types cause food spoilage and crop damage but others are incredibly useful in the production of fermented foods such as yoghurt and soy sauce. Relatively few bacteria are parasites or pathogens that cause disease in animals and plants. 

Bacteria reproduce by binary fission. In this process the bacterium, which is a single cell, divides into two identical daughter cells. Binary fission begins when the DNA of the bacterium divides into two (replicates). The bacterial cell then elongates and splits into two daughter cells each with identical DNA to the parent cell. Each daughter cell is a clone of the parent cell.

When conditions are favourable such as the right temperature and  

nutrients are available, some bacteria like Escherichia coli can divide every 20 minutes. This means that in just 7 hours one bacterium can generate 2,097,152 bacteria. After one more hour the number of bacteria will have risen to a colossal 16,777,216. That’s why we can quickly become ill when pathogenic microbes invade our bodies.