About Bacteria


Phylogenetic Tree of Life

Need to know about bacteria? Beneficial bacteria and probiotics are still just bacteria. To find out more, read on.

Bacteria are unicellular microorganisms, and they form their own domain in the classification scheme of living things. They are found in every earthly environment including the stratosphere. Highly adaptable, they survive in arctic ice, hot springs and hydrothermal vents on the ocean floor. With approximately 5 x 1030 bacteria on earth, their biomass exceeds that of all other plants and animals.

They are easily distinguished from the singular cells that make up other animals. Bacteria have no nucleus and their organelles lack a membrane, which is what scientists call a “prokaryotic” cell type. Cells that have a membrane-bound nuclei and organelles are called “eukaryotic” cells. Most bacteria are 0.5-5.0 μm in length and are invisible to the unaided eye.


Bacteria, along with the unicellular microorganisms of the Archaea domain, were the first forms of life to appear on earth approximately four million years ago. Despite their long history, the human race was unaware of their existence until Antonie van Leeuwenhoek designed his own single lens microscope in 1676 and looked at his own saliva. Other notables in the microbiology world included Louis Pasteur and Robert Koch. Louis Pasteur discovered microorganisms were responsible for the process of fermentation (needed to make beer or wine), and he also developed pasteurization, the sterilization of liquids through high-heat. Robert Koch is considered the founder of modern bacteriology having discovered the infectious agents for tuberculosis, cholera, and anthrax. He firmly proved that infectious agents were at the root of many diseases.

Living things are separated into three main domains: Bacteria, Archaea and Eucarya. The domain Bacteria has undergone many changes in the last few years due to new ways of classifying bacteria using DNA. Current phyla are listed (groups within the domain).

  • Acidobacteria
  • Actinobacteria
  • Aquificae
  • Bacteroidetes
  • Caldiserica
  • Chlamydiae
  • Chlorobi
  • Chloroflexi
  • Chrysiogenetes
  • Cyanobacteria
  • Deferribacteres
  • Deinococcus-Thermus
  • Dictyoglomi
  • Elusimicrobia
  • Fibrobacteres
  • Firmicutes
  • Fusobacteria
  • Gemmatimonadetes
  • Lentisphaerae
  • Nitrospira
  • Planctomycetes
  • Proteobacteria
  • Spirochaetes
  • Synergistetes
  • Tenericutes
  • Thermodesulfobacteria
  • Thermotogae
  • Verrucomicrobia

Identifying Bacteria
One of the first ways that bacteria are identified is through Gram staining. This categorizes bacteria into two groups according to their cell wall type. Bacteria that stain positively have a thick cell wall with a lot of peptidoglycan, while those that are negative have very little peptidoglycan. Peptidoglycan is a substance formed by sugar molecules and amino acids.

Bacterial morphology diagram cs (2)

Morphology of Bacteria
Bacteria are also categorised by shape. Rod-shaped bacteria are “bacilli” types, round-shaped are “cocci” types, and spiral forms are called “spirilla.” Others exist as comma shaped “vibrios.” Their shape influences their ability to move along with the ability to elongate and the possession of flagella. Bacteria with flagella have the ability to swim through water and move relatively as fast as fish.

Bacterial Reproduction
Bacteria reproduce mainly through a system called “binary fission”. This means that an adult bacterium splits itself in two and forms perfect daughter clones. Other systems include “budding”, where a small protrusion forms on an adult bacterium that eventually breaks off and forms a daughter cell. Genetic recombination in these systems is absent, however, there are several methods that bacteria can use to exchange genetic code:

  • Transformation: This is when DNA is encountered in the environment and taken up by the bacteria. The DNA is often from dead bacteria.
  • Transduction: This occurs when foreign DNA is introduced into the bacteria via a bacterial virus called a bacteriophage.
  • Conjugation: This occurs directly between two bacteria. A small tunnel forms between them and allows DNA to be transferred.

What They Eat
Most bacteria are heterotrophic, meaning that they survive off other (previously) living things, like you and leftover food. However, there are also autotrophic bacteria that are capable of producing their own food like plants. These use the process of photosynthesis (producing energy from light) or chemosynthesis (producing energy from carbon molecules) to produce the energy that they need.

The diversity of bacteria is enormous, and they contribute extensively to our well-being. Not only do they directly help us internally, they are also highly important to industry. They are necessary for the production of fermented foods and alcoholic beverages, waste processing, and maintaining the health of plants, soil and water bodies.