Eubacteria, often referred to as “true bacteria,” represent a vast and diverse domain of life characterized by their prokaryotic cell structure. These single-celled organisms lack a membrane-bound nucleus and other complex organelles found in plants and animals. The genetic material consists primarily of a single, circular chromosome located in the cytoplasm’s nucleoid region. This simple organization dictates a method of multiplication fundamentally different from sexual reproduction. Eubacterial multiplication is overwhelmingly asexual, meaning a single parent cell gives rise to genetically identical offspring, allowing for rapid population growth in favorable conditions.
The Primary Method of Multiplication: Binary Fission
The primary mechanism by which eubacteria increase their numbers is called binary fission, a process of simple cell division that does not involve the formation of a spindle apparatus. This asexual reproduction starts with the duplication of the cell’s genetic material, specifically the circular chromosome. Replication begins at a specific site on the chromosome known as the origin of replication, and as the DNA copies, the two resulting origins move toward opposite ends of the cell.
As DNA replication proceeds, the cell begins to elongate, physically pushing the newly synthesized chromosomes apart. This elongation ensures each half of the dividing cell will receive a full copy of the genetic blueprint. Once the chromosomes are separated and positioned at the cell poles, a protein complex begins to assemble at the cell’s midpoint. This complex involves a tubulin-like protein called FtsZ, which forms a ring structure precisely where the division will occur.
The FtsZ ring acts as a scaffold for the synthesis of a new cell wall and cell membrane, which collectively form an inward-growing partition known as the septum. This septum progressively pinches the parent cell in two, eventually resulting in the cleavage of the cytoplasm. The final step sees the complete formation of the new cell wall, which separates the single parent into two separate and typically identical daughter cells. This entire cycle can be remarkably fast; under optimal conditions, some bacteria can complete binary fission and double their population in as little as twenty minutes, leading to exponential growth.
Mechanisms for Genetic Exchange
Although binary fission produces genetically identical cells, eubacteria possess mechanisms to acquire new traits and introduce genetic variation through horizontal gene transfer (HGT). Unlike vertical gene transfer (the passing of genes from parent to offspring), HGT involves the movement of genetic material between organisms of the same generation. This process is not a form of multiplication, as it does not increase the cell count, but it is a powerful driver of bacterial evolution and adaptation.
One method is conjugation, which requires direct physical contact between a donor and a recipient cell. The donor bacterium uses a specialized appendage, known as a conjugation pilus, to establish a bridge between the two cells. Through this bridge, a copy of a small, independently replicating piece of DNA called a plasmid is transferred. These plasmids frequently carry genes that confer a selective advantage, such as resistance to antibiotics.
A second mechanism is transformation, where a bacterial cell takes up “naked” DNA directly from its surrounding environment. This environmental DNA is typically released when another bacterial cell dies and lyses. Only certain bacteria, termed “competent” cells, are naturally able to bind and transport this external genetic material across their cell membrane. Once inside, the new DNA fragment may be incorporated into the host cell’s own chromosome.
The third form of horizontal gene transfer is transduction, which relies on a bacteriophage (a virus that specifically infects bacteria) as the vehicle for DNA transport. When a phage replicates inside a host bacterium, it can sometimes accidentally package a fragment of the host’s bacterial DNA into its viral capsid. This phage then injects the bacterial DNA into a new recipient cell, effectively moving genes from one bacterium to another. These three methods allow for the rapid spread of traits throughout a bacterial population.
Survival Through Endospore Formation
Beyond multiplication and genetic exchange, some eubacteria have developed a specialized strategy for long-term survival in harsh conditions. This is the process of sporulation, which results in the formation of a highly resistant, dormant structure called an endospore. Endospore formation is initiated when the bacterium senses unfavorable environmental changes, such as a lack of necessary nutrients, extreme temperatures, or desiccation.
The process is not a form of reproduction because a single vegetative cell produces only one endospore, meaning there is no increase in cell number. Instead, the bacterium compartmentalizes its genetic material into a specialized spore structure within the original mother cell. This core is surrounded by several protective layers, including a spore coat and a thick cortex layer.
The core is kept in a state of extreme dehydration and contains large amounts of dipicolinic acid, which helps stabilize the DNA against heat damage. These modifications make the endospore one of the most durable cell types in nature. When environmental conditions become favorable again, the endospore can rapidly revert to an active, multiplying vegetative cell in a process known as germination.