Culturing is a foundational technique in biology that involves growing living cells, tissues, or microorganisms in a controlled, artificial environment. This process, often referred to as in vitro growth, allows scientists to study biological processes, isolate specific organisms, and manufacture complex biological products. Researchers prompt proliferation by providing a precise mixture of nutrients and maintaining specific physical conditions.
Essential Requirements for Biological Growth
Successful culturing relies on establishing three controlled conditions: a sterile environment, a specialized nutrient source, and specific physical parameters. A sterile environment is maintained through aseptic technique, which uses sterilized equipment and practices like working under a laminar flow hood. This prevents contamination from airborne microbes that would compete with the desired material.
Culture media, a liquid or gel, provides the necessary chemical components for growth and division. This complex solution contains a carbon source, such as glucose, for energy, along with nitrogen sources, vitamins, and minerals. The specific formulation of the media must be tailored to the cell type being grown, as different organisms have unique nutritional needs.
The final requirement involves the control of physical factors, typically managed using an incubator. Human and mammalian cells are grown at \(37^circ text{C}\), mirroring the body’s internal temperature. The media’s \(text{pH}\) must also be maintained within a narrow range, a balance often regulated by controlling the atmospheric concentration of carbon dioxide inside the incubator.
Methods for Cultivating Microorganisms
Microorganisms are commonly grown using two forms of media: liquid broths and solid agar plates. Liquid broth cultures grow large volumes of an organism for analysis or industrial purposes, resulting in a cloudy suspension of cells. Solid media, made by adding a solidifying agent like agar, allows for the physical separation and isolation of individual cells.
The streak plating method is the primary technique used to separate a single species from a mixed microbial sample. This procedure uses a sterile inoculating loop to physically dilute the sample across the surface of an agar plate in defined sections. The loop is sterilized between each section, progressively reducing the number of organisms transferred.
This methodical dilution results in the final sections containing single, isolated cells that grow into discrete, visible colonies. Since each colony originates from a single precursor cell, picking one yields a pure culture, necessary for accurate identification and study. Colonies grown on solid media can then be transferred to liquid broth for mass production or used for diagnostic testing.
Growing Specialized Cells and Tissues
Culturing cells derived from multicellular organisms requires a higher level of specificity than microbial culture. Researchers often use primary cells, which are freshly isolated from living tissue and maintain physiological relevance. These cells have a limited lifespan and can only divide a finite number of times before undergoing senescence.
For long-term or large-scale studies, researchers often rely on immortalized cell lines, which have been genetically modified to proliferate indefinitely. Examples include the widely used HeLa cells, which are easy to maintain and offer a consistent model for experimentation. Unlike many microorganisms, most specialized cells are anchorage-dependent and must adhere to a treated plastic or glass surface to survive and grow.
The media for specialized cell culture is significantly more complex, often requiring the addition of fetal bovine serum (FBS) or engineered growth factors. This serum supplies the cells with hormones, attachment factors, and other proteins that trigger growth and division, which must be carefully balanced with the controlled \(5%\) \(text{CO}_2\) atmosphere provided by the incubator. Beyond growing simple cell monolayers, advanced techniques like tissue culture allow for the creation of three-dimensional structures, such as organoids, which better mimic the architecture and function of native organs.
Practical Applications of Culturing
The ability to grow and manipulate living biological systems in the laboratory translates into profound real-world applications across medicine and industry. In diagnostic medicine, culturing a patient sample, such as blood or urine, is the most direct way to identify the specific pathogen responsible for an infection. Once the organism is isolated, scientists perform antimicrobial susceptibility testing, where the pathogen is exposed to various antibiotics on an agar plate to determine which medication will be most effective for treatment.
Culturing also serves as a fundamental platform for biomedical research, providing model systems to study complex diseases. For instance, cancer cell lines are routinely used to screen thousands of potential drug compounds in a highly controlled setting, helping researchers understand disease mechanisms and test new therapies before moving to animal models. This allows for the rapid assessment of a compound’s toxicity and effectiveness against human cells.
On an industrial scale, large-volume culturing is the backbone of modern biotechnology and pharmaceutical manufacturing. Many vaccines, including those for polio and hepatitis B, are produced by growing the target virus in vast quantities of animal cell cultures. Furthermore, therapeutic proteins, such as monoclonal antibodies used to treat autoimmune diseases and cancer, are synthesized by genetically engineered cell lines, which are grown in massive bioreactors to produce these life-saving medicines.