Bacterial Population Growth

Microbial Growth Cycle

Increases in cell size are tightly linked in unicellular organisms and under optimal conditions bacteria can grow and divide rapidly.

Learning Objectives

Duplicate the requirements of microbial growth cycles

Key Takeaways

Key Points

  • Bacteria grow to a fixed size and then reproduce through binary fission which a form of asexual reproduction. Under optimal conditions, bacteria can grow and divide extremely rapidly.
  • Different kinds of bacteria need different amounts of oxygen to survive.
  • For microbial growth to process, microorganisms require certain nutrients including carbon, nitrogen, phosphorus, sulfur, and metal ions.
  • Various types of bacteria thrive at different temperatures.

Key Terms

  • binary fission: The process whereby a cell divides asexually to produce two daughter cells.
  • Anaerobe: An anaerobic organism; one that does not require oxygen to sustain its metabolic processes.
  • Aerobe: Any organism (but especially a bacterium) that can tolerate the presence of oxygen or that needs oxygen to survive.

Microbial Growth Cycle

All microbial metabolisms can be arranged according to three principles: 1) How the organism obtains carbon for synthesizing cell mass. 2) How the organism obtains reducing equivalents used either in energy conservation or in biosynthetic reactions. 3) How the organism obtains energy for living and growing (for more detail on this topic see atom on Growth Terminology). Unlike in multicellular organisms, increases in cell size (cell growth and reproduction by cell division) are tightly linked in unicellular organisms. Bacteria grow to a fixed size and then reproduce through binary fission which is a form of asexual reproduction. Under optimal conditions, bacteria can grow and divide extremely rapidly. These optimal conditions are discussed below.

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Metabolic characteristics of microorganisms: This is a flowchart to help determine how a microorganism undergoes growth development.

Oxygen Requirements

Different kinds of bacteria need different amounts of oxygen to survive, which determines which bacteria can infect which parts of the body. They are not able infect the skin because oxygen is present, and they can only grow in the presence of oxygen. Conversely, obligate anaerobes are killed by oxygen and carry out fermentation. Tetanus is an obligate anaerobe so it will infect areas where oxygen in limited. Aerotolerant anaerobes breath anaerobically (without oxygen), but they are able to survive when oxygen is present.

Nutrient Requirements

For microbial growth to process, microorganisms require certain nutrients including carbon, nitrogen, phosphorus, sulfur, and metal ions.

Temperature Requirements

Various types of bacteria thrive at different temperatures. Microorganisms that grow best at moderate temperatures are called mesophiles. Those surviving at high temperatures are thermophiles and microorganisms surviving at very low temperatures are called psychrophiles.

Growth Terminology

The two ways that microbial organisms can be classified are as autotrophs (supply their own energy) or as heterotrophs (use the products of others).

Learning Objectives

Recall bacterial growth terminology

Key Takeaways

Key Points

  • An autotroph, which means self-feeding or producer, is an organism that produces complex organic compounds (such as carbohydrates and proteins) from simple substances present in its surroundings. To produce these organic compounds it either uses energy from light or inorganic chemical reactions.
  • Photoautotrophs are a type of autotroph that use light (sunlight if they are green plants) as their energy source.
  • Chemoautotrophs are also a type of autotroph that derive energy from chemical reactions and synthesize all necessary organic compounds from carbon dioxide.
  • A heterotroph is an organism that, unlike an autotroph, cannot fix carbon and uses organic carbon for growth. Heterotrophs use the products formed by autotrophs to survive.
  • Photoheterotrophs are a type of heterotroph that use light for energy, but cannot use carbon dioxide as their sole carbon source.
  • Chemoheterotrophs are a type of heterotroph that are unable to fix carbon and form their own organic compounds so they must use products formed by autotrophs.

Key Terms

  • autotroph: an organism that can synthesize its food from inorganic substances, using heat or light as a source of energy.
  • heterotroph: An organism which requires an external supply of energy in the form of food as it cannot synthesize its own.

Growth Terminology

The two ways that microbial organisms can be classified are as autotrophs (supply their own energy) or as heterotrophs (use the products of others).

image

Metabolic characteristics of microorganisms: This is a flowchart to help determine how a microorganism undergoes growth development.

Autotrophs

An autotroph, which means self-feeding or producer, is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings. To produce these organic compounds it either uses energy from light (by photosynthesis) or inorganic chemical reactions. Autotrophs reduce carbon dioxide (CO2) by adding hydrogen atoms to it. This reduction process forms an organic compound that stores chemical energy. Most autotrophs use water as their reducing agent (to gain hydrogen atoms), but some can use other hydrogen compounds like hydrogen sulfide. Autotrophs, and their formation of organic compounds, are an important component of the food chain because they produce the food necessary for larger, more complex organisms to grow.

Photoautotrophs

Photoautotrophs are a type of autotroph. Photoautotrophs use light (sunlight if they are green plants) as their energy source. They use this energy (physical) and convert it into chemical energy in the form of reduced carbon. This process produces energy that carries out various cellular metabolic processes.

Chemoautotrophs

Chemoautotrophs are also a type of autotroph. They derive their energy from chemical reactions and synthesize all necessary organic compounds from carbon dioxide. Most chemoautotrophs are bacteria and archaea that live in hostile environments (such as deep sea vents). Chemoautotrophs are thought to be the first organisms to inhabit earth.

Heterotrophs

A heterotroph is an organism that, unlike an autotroph, cannot fix carbon and uses organic carbon for growth. Heterotrophs use the products formed by autotrophs to survive.

Photoheterotrophs

Photoheterotrophs are a type of heterotroph. These organisms use light for energy, but cannot use carbon dioxide as their sole carbon source. They use compounds formed by autotrophs (such as carbohydrates, fatty acids, and alcohols) as their food.

Chemoheterotrophs

Chemoheterotrophs are a type of heterotroph. They are unable to fix carbon and form their own organic compounds so they must use products formed by autotrophs. These organisms use inorganic energy sources or organic energy sources to sustain life.