Microbiology Terms Starting With B

Bacillus is both a general term for a rod-shaped bacterium and the formal genus name for a group of gram-positive, endospore-forming bacteria common in soil, food, and clinical microbiology.

In morphology, bacillus describes a bacterial cell with a rod-like shape, as opposed to cocci, which are spherical, or spirilla, which are spiral-shaped. Taxonomically, Bacillus with a capital B refers to a specific genus of aerobic or facultatively anaerobic, spore-forming bacteria. The species Bacillus subtilis is a major model organism for studying bacterial chromosome replication, cell division, and sporulation, while Bacillus anthracis causes anthrax and produces environmentally persistent endospores.

Bacillus thuringiensis produces insecticidal crystal proteins used in biological pest control, showing that the same genus contains research tools, agricultural allies, and serious pathogens.

Bacteria are single-celled prokaryotic microorganisms with peptidoglycan-containing cell walls, no membrane-bound nucleus, and diverse metabolisms that allow them to inhabit nearly every environment on Earth.

Bacteria reproduce mainly by binary fission, and fast-growing species such as Escherichia coli can divide in about 20 minutes under ideal laboratory conditions. Their compact genomes, plasmids, and capacity for horizontal gene transfer allow rapid adaptation to antibiotics, immune pressure, and changing environments. Bacteria occupy habitats ranging from boiling hydrothermal vents and acid mine drainage to Antarctic ice, plant roots, and the human gut.

A minority cause disease, but most are harmless or beneficial, recycling nutrients, fixing nitrogen, fermenting foods, synthesizing vitamins, and shaping immune development in animals.

Bacterial Metabolism is the full set of chemical reactions bacteria use to obtain energy, acquire carbon, build cellular components, and maintain life under specific environmental conditions.

Bacterial metabolism is far more diverse than animal metabolism because bacteria use many different energy sources, carbon sources, and terminal electron acceptors. Aerobic heterotrophs oxidize organic compounds with oxygen, while anaerobic respirers use nitrate, sulfate, iron, or carbon dioxide when oxygen is absent. Phototrophic bacteria capture light energy, chemolithotrophs oxidize inorganic chemicals such as ammonia or hydrogen sulfide, and fermenters generate ATP without an external electron acceptor.

This diversity drives major biogeochemical cycles, including carbon fixation, nitrification, sulfur oxidation, methane production, and decomposition in soils, oceans, sediments, and host-associated microbiomes.

Bacteriophage is a virus that infects bacteria, replicating inside bacterial cells and often shaping bacterial evolution through lysis, lysogeny, and horizontal gene transfer.

A bacteriophage attaches to specific receptors on the bacterial surface, injects its genetic material, and then follows either a lytic or lysogenic pathway. During the lytic cycle, the phage redirects host machinery to make viral components and bursts the cell to release new particles. Lysogenic infection instead places the phage genome in the bacterial chromosome as a prophage, where it is copied with the host until induction triggers lytic replication.

Phages are the most abundant biological entities in many environments, influence marine nutrient cycling by killing bacteria, and are being investigated as targeted therapies for antibiotic-resistant infections.

Binary Fission is the asexual division process in which one prokaryotic cell replicates its chromosome, segregates the copies, and splits into two daughter cells.

Binary fission begins when the bacterial chromosome starts replication at the origin and newly copied DNA moves toward opposite regions of the elongating cell. The tubulin-like protein FtsZ assembles into a Z-ring at midcell and recruits the divisome, the protein machinery that builds the septum. Peptidoglycan synthesis closes the septum, membranes constrict, and the parent cell separates into two daughters that are usually genetically identical unless mutation or horizontal gene transfer has occurred.

Growth rate depends strongly on species and environment, ranging from minutes in very fast-growing bacteria to many hours in slow pathogens such as Mycobacterium tuberculosis.

Biofilm is a structured microbial community attached to a surface and embedded in a self-produced extracellular matrix of polysaccharides, proteins, lipids, and extracellular DNA.

Biofilm formation begins when planktonic cells attach reversibly to a surface, strengthen that attachment, form microcolonies, and secrete an extracellular polymeric matrix. Cells inside the biofilm experience gradients of oxygen, nutrients, pH, and waste products, so microbes only micrometers apart can behave very differently. Biofilm cells are commonly 10 to 1,000 times more tolerant of antibiotics than free-living cells because the matrix slows penetration, cells grow more slowly, and stress-response pathways are activated.

Clinically important biofilms form on teeth, catheters, prosthetic joints, heart valves, and cystic fibrosis airways, where they contribute to chronic and recurrent infections.

Biosafety Cabinet is a ventilated laboratory enclosure that uses controlled airflow and HEPA filtration to reduce worker, sample, and environmental exposure to infectious aerosols.

A Class II biosafety cabinet draws room air inward through the front opening, passes air through high-efficiency particulate air filters, and directs clean air over the work surface while exhausting filtered air. HEPA filters remove 99.97 percent of particles that are 0.3 micrometers in diameter, including most bacteria-containing droplets and many aerosolized particles. Class I cabinets protect the worker and environment but not the sample, Class II cabinets protect all three, and Class III cabinets are sealed gloveboxes used for the highest-risk agents.

Good technique includes slow arm movements, uncluttered work surfaces, verified airflow, and sterile disposable tools or approved electric sterilizers rather than open flames, which can disrupt airflow and create fire hazards.

Broad-Spectrum Antibiotic is an antimicrobial drug active against many bacterial groups, often including both gram-positive and gram-negative species.

Broad-spectrum antibiotics target bacterial processes shared across many taxa, such as protein synthesis, DNA replication, or cell wall assembly. They are valuable for empiric treatment when a serious infection must be treated before culture results identify the causative organism. Their breadth also creates tradeoffs, because they disrupt normal microbiota and can select for resistant organisms across many bacterial species at once.

Fluoroquinolones, tetracyclines, third-generation cephalosporins, and carbapenems are common broad-spectrum classes, though the exact spectrum varies by drug and by local resistance patterns.