9.1: How Microbes Grow

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• As a culture medium accumulates toxic waste and nutrients are exhausted, cells die in greater and greater numbers. Soon, the number of dying cells exceeds the number of dividing cells, leading to an exponential decrease in the number of cells

• In eukaryotic organisms, the generation time is the time between the same points of the life cycle in two successive generations.

• The bacterial cell cycle involves the formation of new cells through the replication of DNA and partitioning of cellular components into two daughter cells.

• In prokaryotes, reproduction is always asexual,

• Most bacteria have a single circular chromosome; however, some exceptions exist.

• The most common mechanism of cell replication in bacteria is a process called binary fission

• Before dividing, the cell grows and increases its number of cellular components. Next, the replication of DNA starts at a location on the circular chromosome called the origin of replication, where the chromosome is attached to the inner cell membrane. Replication continues in opposite directions along the chromosome until the terminus is reached.

• The center of the enlarged cell constricts until two daughter cells are formed, each offspring receiving a complete copy of the parental genome and a division of the cytoplasm (cytokinesis)

• This process of cytokinesis and cell division is directed by a protein called FtsZ. FtsZ assembles into a Z ring on the cytoplasmic membrane

• The divisome activates to produce a peptidoglycan cell wall and build a septum that divides the two daughter cells.

• This definition is not practical for bacteria, which may reproduce rapidly or remain dormant for thousands of years.

• In prokaryotes (Bacteria and Archaea), the generation time is also called the doubling time and is defined as the time it takes for the population to double through one round of binary fission.

• Before dividing, the cell grows and increases its number of cellular components. Next, the replication of DNA starts at a location on the circular chromosome called the origin of replication, where the chromosome is attached to the inner cell membrane.

• The Z ring is anchored by FtsZ-binding proteins and defines the division plane between the two daughter cells.

• Additional proteins required for cell division are added to the Z ring to form a structure called the divisome.

• The daughter cells are separated by the division septum, where all of the cells’ outer layers (the cell wall and outer membranes, if present) must be remodeled to complete division.

• Microorganisms grown in closed culture (also known as a batch culture), in which no nutrients are added and most waste is not removed, follow a reproducible growth pattern referred to as the growth curve.

• The culture density is defined as the number of cells per unit volume.

• The culture density is defined as the number of cells per unit volume

• culture density is also a measure of the number of cells in the population.