Gram Positive and Gram Negative Bacteria

Bacteria were one of the earliest forms of life to appear on the planet. It is estimated that 3.5 billion years ago, the planet was home to a population of single-celled organisms, which is about the same time that life on the planet began. During that time, bacteria were a predominant form of life and there were many complex and advanced bacteria on the planet. However, many scientists argue that life on earth originated from a single cell.

About Bacteria

Bacteria are microscopic organisms that live in or on other living organisms and are capable of altering or degrading their host cells. Most bacteria live in an aqueous environment and are found in the soil, water and air. Bacteria are  important for life on Earth because they provide energy and break down waste. They are responsible for decaying unnecessary biological materials in the soil and recycling nutrients via the process of respiration and elemental fixation. 

Bacteria also maintain symbiotic relationships with different plants and boost their respiratory and photosynthetic processes. 

Classification of Bacteria

Bacteria is a cosmopolitan organism, which means bacteria exist everywhere. Bacteria also exist in uninhabitable places such as hydrothermal vents, extreme cold glaciers, marshlands etc. These bacteria have evolved and developed physiological, and behavioural adaptability to the habitat by enhancing their mechanisms to thrive in stressful habitats. 

Bacteria are classified into gram-positive and gram-negative, Aerobic and Anaerobic, Autotrophic and Heterotrophic based and different structural, physiological and behavioural distinguishes.

Aerobic Bacteria 

Aerobic bacteria are the type of bacteria which synthesise their food material by photosynthesis and utilise oxygen for cellular respiration and other processes. As the name implies aerobic bacteria are the type of bacteria that can obligately and/or facultatively thrive in an oxygen-rich environment. The oxygen utilised from water during the photosynthetic process serves as the electron acceptor in the photosynthetic processes.

The amount of metabolic energy produced by Aerobic bacteria in cellular metabolic processes exceeds the energy produced by anaerobes. 

The most common types of aerobic bacteria are Mycobacterium, Tuberculosis, Lactobacillus etc. 

Anaerobic Bacteria

Anaerobic bacteria are the type of bacteria that can exist even in places devoid of oxygen. Anaerobic bacteria do not utilise oxygen-containing compounds for photosynthetic and cellular processes. Anaerobic bacteria are mainly found in regions with low or no oxygen concentration. Anaerobic bacteria predominantly utilise sulphur compounds as an electron acceptors in their photosynthetic processes. 

Anaerobic bacteria produce less metabolic energy than aerobes through their photosynthetic and cellular processes. 

Most common examples of Anaerobic bacteria are Methanogens (methane-producing bacteria), Clostridium family and Staphylococcus. 

Autotrophic Bacteria

An autotrophic bacteria is a microorganism that can produce its own sustenance. Autotrophic bacteria consume inorganic material and convert them into organic nutrition. Since they’re the primary producers at the bottom of all food chains, autotrophic bacteria are crucial to all life. There two types of Autotrophs, Photo autotrophs utilise sunlight for their photosynthetic processes. Chemoautotrophs use energy from chemical compound breakdown for their metabolic processes. Common examples of autotrophs include- Nitrosomonas, Nostoc, and Anabaena. 

Heterotrophic Bacteria

Heterotrophic bacteria, sometimes known as decomposers, feed mostly on dead plants and animals. Some bacteria, known as scavengers or detritivores, specialise in feeding on decaying organic debris. Even some life forms are heterotrophic, parasitizing the thallus of other species and receiving their own sustenance in this way. Saprophytic bacteria are bacteria that do not produce chlorophyll.

Common examples of heterotrophs include – Salmonella, Xanthomonas, and Agrobacterium.

Key Differences between Gram-Positive and Gram-Negative Bacteria

 The Gram’s Staining test was developed in 1884 by a Dutch bacteriologist Hans Christian Gram. The Gram’s staining test paves the way to distinguish bacteria into two major groups namely gram-positive and gram-negative bacterium. 

Gram-Positive Bacteria

1. The members of the Gram-Positive Bacteria comprise of thick peptidoglycan wall, hence take up the Gram’s solution which is crystal violet. As the Gram-Positive Bacteria takes up the Gram’s solution the root word “Positive” is added to the name.
2. Gram-Positive Bacteria have a very complex cell wall structure which comprises polysaccharides, and the unique composition of their cell wall is teichoic acids. The cell wall of a gram-positive bacterium also comprises specific proteins and peptidoglycan and lipid chains. 
3. Most Gram-Positive Bacteria are harmless and are used for industrial purposes. 
4. The peptidoglycan chains in gram-positive bacteria comprise N acetyl glucosamine, and N acetyl muramic acid and do not contain a cytoplasmic inner layer. 
5. The exchange of genetic material in Gram-Positive bacteria occurs by horizontal gene exchange and conjugation. 
6. Common examples of Gram-Positive bacteria are Streptococcus and Bacillus family.

Gram-Negative Bacteria

1. The members of Gram-Negative Bacteria possess a thin layer of peptidoglycan wall hence, they do not retain Gram’s Solution Crystal Violet. As the Gram-Negative bacteria does not show the gram stain test, the root word “Negative” is added to the name. 
2. The peptidoglycan slimy layer of the gram negative bacteria comprises lipids and predominantly liposaccharides. 
3. The lipoprotein chains are attached to the peptidoglycan base in the outer thin wall of the Gram-Negative bacteria. 
4. Teichoic acids and lipoteichoic acids are absent in the thin wall of gram negative bacteria.
5. Exchange of genetic material takes place by Transduction. 
6. Common examples of Gram-Negative Bacteria are Helicobacter, Haemophilus influenzae and Pseudomonas.

Conclusion

Bacteria are single-celled organisms that live in both soil and water. Bacteria are important to our ecosystem and help build the soil, decompose food and provide us with energy, but some bacteria are harmful and can cause food poisoning. Bacteria and their products are also used for domestic development, for example, lactobacillus is used to convert pasteurised milk to yoghurt.