Microbial cell structure, growth, bacterial gene transfer, and viruses.
Binary fission is the asexual reproduction method by which most bacteria duplicate. A single circular chromosome is copied, the cell elongates, and a protein‑based Z‑ring constricts the middle, producing two genetically identical daughter cells.
Transduction is the bacteriophage‑mediated transfer of DNA between bacteria. In generalized transduction any part of the donor genome can be moved, while specialized transduction transfers only specific genes located next to the prophage integration site.
Bacterial conjugation is a direct, pilus‑mediated transfer of genetic material—usually a plasmid—from a donor (F⁺) cell to a recipient (F⁻) cell. This process spreads traits such as antibiotic resistance and underpins many laboratory tools for genetic engineering.
Bacterial chromosomes are essential, single circular DNA molecules that carry the core genetic information, while plasmids are smaller, often circular DNA elements that replicate independently and usually hold non‑essential traits such as antibiotic resistance. Understanding their structural and functional distinctions reveals how bacteria store vital genes and acquire new capabilities.
Bacteriophages can reproduce by either the lytic cycle, which kills the host cell by bursting it, or the lysogenic cycle, in which the viral genome integrates into the bacterial chromosome and replicates silently until induction. The two strategies differ in timing, genetic integration, and ecological impact.
Gram‑positive and Gram‑negative bacteria differ mainly in the structure of their cell envelope: Gram‑positives have a thick peptidoglycan layer and no outer membrane, while Gram‑negatives possess a thin peptidoglycan layer, an outer membrane with lipopolysaccharide, and a periplasmic space. These differences affect staining, antibiotic entry, and immune recognition.
Bacterial transformation is the process by which a competent cell directly absorbs free DNA from its environment, incorporates it into its genome, and expresses the new genes. It can occur naturally under specific conditions or be induced artificially for laboratory purposes.
Bacterial populations grown in a closed system pass through four predictable phases—lag, logarithmic (log), stationary, and death. Each phase reflects a distinct balance between cellular processes such as nutrient uptake, biosynthesis, and waste accumulation, and together they form the classic bacterial growth curve used in microbiology labs.
Food spoilage occurs when biological, enzymatic, or chemical changes make food unacceptable to eat. The primary drivers are microorganisms—bacteria, yeasts, and molds—along with the food’s own enzymes and environmental factors such as temperature and oxygen.
Bacteria exchange genetic material without sex through three main processes—transformation, transduction, and conjugation—collectively called horizontal gene transfer. These mechanisms generate diversity, spread traits such as antibiotic resistance, and shape microbial evolution.