Bacterial growth: Physical, and Chemical requirements:

What is Bacterial growth?

         In a process known as binary fission, bacterial growth occurs when a bacterium divides into two daughter cells. The daughter cells that are produced have the same genetic makeup as the original cell, assuming no incident occurs. Because of this, bacteria flourish. The bacterial population, however, experiences exponential growth if the average survival rate exceeds unity.

      The measuring of an exponential bacterial growth curve in batch culture has historically been a need for all microbiologists; the fundamental approach cells for bacterial enumeration (cell counting) by direct and individual (microscopic, flow cytometry), direct and bulk (biomass), indirect and individual (colony counting), or indirect and bulk (most probable number, turbidity, nutrient uptake) methods. Theory and observations are reconciled via models.

What is generation time?

  • The change in bacterial population per unit of time is used to calculate a bacterium’s growth rate.
  • The amount of time needed for a bacterium to generate two daughter cells under ideal circumstances is known as the generation time.
  • The majority of harmful bacteria, including E. coli take around 20 minutes.
  • For Mycobacterium tuberculosis, the generation time is longer (20 hours), and for M, it is the longest (20 days). leprae.
  • Within 24 hours, a bacteria produce millions of cells through fast cell division and replication.

What are the factors affecting the growth of bacteria?

      Temperature, pH, moisture content, nutrients available, and the features of other organisms present all significantly impact the proliferation of microbes whether they are found in the body, in nature, or a lab.

  • Temperature
  • Ph
  • Osmotic pressure


      Most harmful bacteria prefer a temperature of 37 C as their ideal environment. The ideal temperature, however, varies; by their temperature range, bacteria are grouped according to their rates of growth as follows:


            Are cold-loving bacteria that can thrive in temperatures between 0 and 20 °C. These organisms make up the majority of soil and aquatic saprophytes.


         Are organisms that prefer a moderate temperature range (between 25 and 40 °C). This category includes the majority of harmful microorganisms.


        These are microorganisms that enjoy being hot. They may thrive at temperatures as high as 55 to 80 degrees B. Stearothermophilus is one illustration.


    The pH of a solution, also known as the level of acidity or alkalinity, is another physical criterion. The ideal pH range for most bacteria is between 6.5 and 7.5. These neutrophilic bacteria typically thrive in the body because the pH of the majority of human tissue is between 7.0 and 7.2. Some bacteria, such as those found in yogurt and sauerkraut, prefer acidic conditions with a pH of 6.0 or lower. It is claimed that these bacteria are acidophilic. Among other typical acidophilic bacteria are molds and yeasts.

Osmotic pressure:

      Microorganisms need water to flourish because the water around them contains nearly all of the nutrients they need in the solution. Extreme halophiles are organisms that can adapt to extremely high salt concentrations, while obligatory halophiles are bacteria that must have the ideal salt concentration for growth. Some microorganisms can grow in salt concentrations of up to 2% even if they don’t require it for growth (a concentration that inhibits the growth of many other organisms). These are referred to as facultative halophiles.

What is the chemical or nutritional requirement for bacterial growth factor?

            Microorganisms need to have access to water as well as a variety of other resources, such as mineral elements, growth stimulants, and gases like oxygen, to flourish. Whether they are proteins, fats, carbs, or lipids, virtually all chemical compounds in microbes contain carbon in some manner.

  • Carbon
  • Nitrogen
  • Oxygen


            All organic molecules have carbon as their skeleton or backbone, making it the primary constituent of biological macromolecules. Another significant chemical, hydrogen, is involved in the majority of microbes’ operations for producing energy. Many bacteria depend on oxygen for their respiration, but nitrogen is necessary for the production of proteins, nucleic acids, and other significant compounds like ATP.

         Microorganisms also require sources of energy and electrons to grow, in addition to the elements carbon, hydrogen, and oxygen. Based on their dietary needs, they can be divided into classes.

Heterotrophs and Autotrophs:

                                   Depending on the source of carbon that an organism prefers to use, microorganisms can be categorized as either heterotrophs or autotrophs. As their only or primary source of carbon, autotrophs can consume carbon dioxide (CO 2). Heterotrophs are organisms that obtain their carbon from reduced, prepared organic compounds.

Chemotrophs and Phototrophs:

                                        Chemotrophs get their energy from oxidizing chemical substances, whilst Phototrophs get their energy from using light (either organic or inorganic). There are just two sources of electrons in microorganisms as well.

Lithotrophs and Organotrophs:

                                     Lithotrophs (sometimes known as “rock-eaters”) obtain their electrons from reduced inorganic materials, whereas organography takes them from organic chemicals.


               Proteins, amino acids, DNA, and RNA are all created using nitrogen. Nitrogen-fixing bacteria are those that take their nitrogen supply straight from the atmosphere. They include soil-found Rhizobium and Azotobacter species.


                 According to their need for oxygen, bacteria can be roughly divided into aerobic and anaerobic microorganisms.

Aerobic bacteria:

For their development, they need oxygen. These include:

  • Aerobes that are required to grow in the presence of oxygen (e.g., P. aeruginosa).
  • Facultative aerobes are common aerobes that can also survive without oxygen (e.g., E. coli). Aerobes that can fly represent the majority of harmful bacteria.
  • Microaerophilic bacteria are those that can flourish in conditions of low oxygen and low (4%) carbon dioxide concentration (e.g., Campylobacter jejuni).

Although some fermentative organisms (such as Lactobacillus Plantarum) are aerotolerant, they lack catalase or superoxide dismutase enzymes.

Since oxygen is not oxidized, neither nascent oxygen (O2) nor hydrogen peroxide (H2O2) is formed.     

Anaerobic bacteria:

  • Obligate anaerobes are bacteria that can grow only in the absence of oxygen (e.g., Clostridium botulinum, Clostridium tetani, etc.).
  • These bacteria lack superoxide dismutase and catalase; hence oxygen is lethal to these organisms.

Chemical nutrients factor affecting growth :

Chemical nutrients include hydrogen, Sulphur, Phosphorous, trace elements and growth factors:


           Sulfur is required for the synthesis of several vitamins and amino acids that include sulphur. Sulfates, hydrogen sulphide, or sulfur-containing amino acids may all be used as sulphur sources, depending on the organism.


                      For the synthesis of phospholipids, DNA, RNA, and ATP, phosphorus is required. The main source of phosphorus is phosphate ions.

Trace elements:

            Like potassium, magnesium, calcium, and iron, trace elements, which are needed in extremely small quantities, typically serve as cofactors in enzyme reactions. They consist of ions of cobalt, manganese, sodium, zinc, copper, molybdenum, and copper. During enzyme processes, cofactors often serve as electron donors or acceptors.

Growth Factor:

             Organic substances that a cell needs for growth but cannot produce on its own include vitamins, amino acids, purines, pyrimidines, and other growth factors.

Organisms with intricate nutritional needs and a high need for growth nutrients are referred to as finicky.

   What is the summary of bacterial growth?

  • Bacteria can be classified as psychrophils, mesophils, thermophils, or hyperthermophils based on the minimum, optimal, and maximum temperatures at which they can grow.
  • The amount of heterogeneity that bacteria exhibit in their needs for gaseous oxygen is astounding. The majority belong to one of the following categories: microaerophils, obligatory anaerobes, facultative anaerobes, or aerotolerant anaerobes.
  • Based on their preferred pH conditions, microorganisms can be classified as neutrophiles, acidophiles, or alkaliphiles.
  • The osmotic environment of a bacterium can influence bacterial development.
  • According to their method of obtaining energy, bacteria can be classified as phototrophs or chemotrophs.
  • Bacteria can be categorized into three classes based on their optimal growth temperature: psychrophiles, mesophils, and autotrophs. Bacteria can also be categorized based on their carbon supply as either autotrophs or heterotrophs.
  • All living things in nature can be categorized into one of four types based on their dietary habits: photoautotrophs, photoheterotrophs, chemoautotrophs, and chemoheterotrophs.
  • For growth, bacteria also require a source of nitrogen, certain minerals, and water.
  • Fastidious organisms are those with complex nutritional needs and numerous growth stimuli.


Rimsha Bashir
Rimsha Bashir

Rimsha Saith is a highly knowledgeable microbiologist with a keen interest in the field. Her expertise and passion are in her writing for Microbiology. As a writer, Rimsha has authored numerous articles that have been well-received by both health and medical students and industries.

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