Bacterial Nutrition and Growth Explained

• Lecture topic is Microbial Growth & Basic Nutritional Requirements

Learning Objectives

• Gain an undertanding of the microbial growth curve and what happens in each phase.
• Learn about different types of microbial reproduction and its underlining process.
• Know the basic nutritional requirements for microorganisms.
• Learn about the importance of each requirement
• Understand the classification of bacteria based on nutritional requirements

Microbial Growth

• Microbiologists study microbial growth as populations.
• They do not follow the growth of each cell individually.
• Population growth is studied by analyzing the growth curve of a microbial culture.

Growth Curve

• A standard bacterial growth curve describes the growth stages of bacteria. Bacteria added to fresh media go through four distinct phases of growth:
  • Lag phase
  • Log or Exponential phase
  • Stationary phase
  • Death or Decline phase

Lag phase

• Bacteria adjust and adapt to new conditions.
• Chemical differences between two media or habitats result in a lag in division.
• During this time, cells may increase in size, but do not undergo binary fission, so the population size doesn't increase

Log phase (logarithmic phase, exponential phase)

• Cells begin to divide.
• This is a period of most rapid growth
• The number of cells produced is greater than the number of cells dying
• Cells are at highest metabolic activity.
• Cells are most susceptible to adverse environmental factors, such as radiation and antibiotics, at this stage.

Stationary Phase

• Population size begins to stabilize.
• Number of cells produced is equal to the number of cells dying, so the overall cell number does not increase.
• Cell division begins to slow down because of factors that include:
  • Accumulation of toxic waste materials
  • Acidic pH of media
  • Limited nutrients
  • Insufficient oxygen supply

Death or Decline Phase

• Population size begins to decrease or decline.
• The number of cells dying is greater than the number of cells produced Cells lose their ability to divide
• A few cells may remain alive for a long period of time.

Microbial Reproduction

• Asexual reproduction results in offspring that are genetically identical to the parent organism.
• Sexual reproduction results in offspring that are genetically different from the parent organisms.

Asexual Reproduction

• Bacteria and archaea reproduce asexually only.
• Eukaryotic microbes can engage in either sexual or asexual reproduction.
• Three different types of microbial asexual reproduction:
  • Binary fission
  • Budding
  • Fragmentation

Binary fission (Transverse fission)

• This is the most common type of reproduction under favorable conditions
• Occurs when a cell divides into two similar daughter cells.
• During the process, bacterial DNA attaches to the cell membrane and starts to replicates itself.
• As the cell enlarges, the replicated DNA separates.
• A cross wall forms that divides the cell into 2 daughter cells.
• The daughter cells soon grow to maturity within 20 – 30 min.

Budding

• A small protuberance, called a bud, develops at one end of the cell.
• Genome replication follows, and one copy of the genome gets into the bud.
• Then the bud enlarges and eventually becomes a daughter cell
• Finally separates from the parent cell.

Fragmentation

• A new organism grows from a fragment of the parent.
• Each fragment develops into a fully grown individual.
• Fragmentation is seen in many organisms, such as animals (some annelid worms and sea stars), fungi, and plants.
• Mostly during unfavorable conditions, bacterial protoplasm undergoes compartmentalization and subsequent fragmentation.
• This process forms minute bodies called gonidia.
• Under favorable conditions, each gonidium grows to a new bacterium.
• Prior to fragmentation the bacterial genome has to undergo repeated replication so that each fragment gets a copy of it.

Viral Reproduction

• Viruses are obligate intracellular parasites.
• Viruses carry their genome (RNA or DNA) and sometimes functional proteins that are required for early steps in the replication cycle.
• Viruses depends on host cell machinery to complete the replication cycle.
• They must commandeer that machinery to successfully replicate.
• Steps in Viral Replication:
  • A. Attachment
  • B. Penetration
  • C. Uncoating

Basic Nutritional Requirement

• Elements of the surrounding environment required by bacteria for energy production, growth, and cellular biosynthesis are nutrients or nutritional requirements

Basic Nutritional Requirements

• Basic nutritional requirements for the growth and multiplication of bacteria are:
  • Water
  • Energy
  • Carbon
  • Nitrogen
  • Inorganic Salts
  • Growth Factor

Water

• Water is the main component of bacterial cells.
• About 70% of the total weight of bacteria consist of water.
• It is used to dissolve all the nutrients so that they can enter thecell easily.
• Required during metabolic reactions.

Energy

• A source of energy may be light (the sun or lamps) or inorganic substances like sulfur, carbon monoxide, or ammonia, or organic matter like sugar, protein, fats, etc.

Carbon

• Many bacteria use compounds which contain carbon (glucose, amino acids, fatty acids, nitrogen) as building blocks to synthesize cell components

Nitrogen

• A typical bacterial cell is 12-14 % nitrogen of dry weight.
• It is needed to synthesize proteins & nucleic acid.

Inorganic Salts

• Phosphorus is required for the synthesis of nucleic acids, membrane phospholipids, and nucleotides like ATP.
• Sulphur is required for the synthesis of sulfur-containing amino acids like cystein and methionine
• Potassium is required for the activity of many enzymes, especially those involved in protein synthesis.

Growth Factors

• Growth factors are certain organic compounds required in very small amount by particular bacteria as they are not capable of synthesizing.
• Also called essential organic compounds.
• Fastidious bacteria require a variety of growth factors.

Classification of Bacteria

• Bacteria are divided into two major groups on the basis of nutrition:
  • Autotrophic bacteria
  • Heterotrophic bacteria

Autotrophic Bacteria

• Bacteria which synthesize their own food are called autotrophic bacteria.
• They use carbon dioxide as the main source of carbon.
• The source of energy for the autotrophs may be either light or chemical.
• They are classified as :
  • Photoautotrophic
  • Chemoautotrophic

Photoautotrophic Bacteria

• Synthesize food using the light energy of the sun, carbon dioxide, and water.
• For example: Purple Sulfur bacteria

Chemoautotrophic bacteria

• Synthesize food using chemical energy.
• They do not require sunlight, therefore, they include bacteria which are found deep in the soil where sunlight does not reach.
• Example: nitrogen-fixing bacteria.
• These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen that will produce ammonia
• This ammonia is used by the bacteria to make their own organic compounds.

Heterotrophic Bacteria

• Those bacteria which obtain their organic food from other organisms are called Heterotrophs.
• Most of these heterotrophic bacteria are pathogenic, causing serious diseases in the host organisms.

Explore bacterial nutrition, differentiating between chemoautotrophs, photoautotrophs, and heterotrophs. Understand the role of nitrogenase in nitrogen fixation. Learn about bacterial growth phases and factors affecting microbial growth.