--- title: "Microbiology" description: "20 topics in Science, in the order they build on each other." canonical: https://lightmysky.com/learn/science/areas/microbiology source: https://lightmysky.com/learn/science/areas/microbiology.md retrieved: 2026-09-02 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Microbiology 20 topics in Science, in the order they build on each other. Page: https://lightmysky.com/learn/science/areas/microbiology - [Bacterial Cell Envelopes and What the Gram Stain Reveals](https://lightmysky.com/learn/science/bacterial-cell-envelopes-and-what-the-gram-stain-reveals-mt_Q5zM0oO3Vu): Bacteria differ in how their wall is built: a thick peptidoglycan layer outside the membrane, or a thin one sandwiched under a second outer membrane. The stain that separates the two works because those structures hold or release dye differently, which is why it predicts so much else. - [Archaea: Different Membranes, Extreme Habitats, Separate Domain](https://lightmysky.com/learn/science/archaea-different-membranes-extreme-habitats-separate-domain-mt_isKmuoGgAn): Archaea build their membrane lipids with ether links and branched chains rather than ester links and straight chains, which holds up under heat, salt and acid. Their transcription and translation machinery is closer to ours than to that of bacteria, which is why they are a separate domain. - [Microbial Growth: Generation Time, Growth Curves and Continuous Culture](https://lightmysky.com/learn/science/microbial-growth-generation-time-growth-curves-and-continuous-culture-mt_ltzgjIBytk): A population that doubles at a fixed interval grows exponentially, so counts are handled on a log scale and generation time is read from the slope. A closed flask passes through lag, exponential, stationary and death phases, while a chemostat holds a culture in one phase by feeding it steadily. - [Controlling Growth: What Sterile Means and How It Is Achieved](https://lightmysky.com/learn/science/controlling-growth-what-sterile-means-and-how-it-is-achieved-mt_j1kqpjUMzk): Heat, radiation, filtration and chemicals each kill or remove microbes by a particular mechanism, and each has organisms it handles badly. Killing follows a rate rather than an instant, so sterilisation is defined by how far the count is driven down. - [Metabolic Diversity: Choosing an Electron Donor and Acceptor](https://lightmysky.com/learn/science/metabolic-diversity-choosing-an-electron-donor-and-acceptor-mt__2yCr9OSIn): Microbes are classified by where they get carbon, where they get energy and what they pass electrons to at the end. The energy available depends on the gap between donor and acceptor, which is why oxygen respirers outgrow the alternatives when oxygen is present. - [Virus Structure and Classification by Genome Type](https://lightmysky.com/learn/science/virus-structure-and-classification-by-genome-type-mt_u2-ecQEwwn): A virus is a genome in a protein coat, sometimes wrapped in a membrane taken from a host. Grouping viruses by whether the genome is DNA or RNA, single or double stranded, and which way it reads predicts what has to happen first inside the cell. - [Viral Life Cycles: Lysis, Lysogeny and Latency](https://lightmysky.com/learn/science/viral-life-cycles-lysis-lysogeny-and-latency-mt_OI8-dySb5A): A virus can replicate at once and burst the cell, or integrate and be copied quietly with the host genome until conditions change. The choice is a regulated decision, not an accident, and it explains why some infections recur years later. - [Bacteriophages as Predators and as Laboratory Tools](https://lightmysky.com/learn/science/bacteriophages-as-predators-and-as-laboratory-tools-mt_vOnjSpXjrj): Phages shape bacterial populations in the wild and were the system in which much of molecular genetics was first worked out. Their specificity for a host strain is what makes them useful for typing bacteria and for delivering genes. - [Operon Logic: Induction, Repression and Feedback on Transcription](https://lightmysky.com/learn/science/operon-logic-induction-repression-and-feedback-on-transcription-mt_yNvJjGMSJQ): Bacteria group related genes under one promoter and switch the whole set on or off with a repressor or activator that senses a small molecule. Whether the default is on or off depends on whether the pathway breaks something down or builds it. - [Horizontal Gene Transfer: Uptake, Contact and Delivery](https://lightmysky.com/learn/science/horizontal-gene-transfer-uptake-contact-and-delivery-mt_mrmn0_nQf7): Bacteria acquire genes from other cells by taking up free DNA, by direct contact through a pilus, or by delivery inside a phage particle. Because transfer crosses species lines, a bacterial family tree drawn from one gene can disagree with one drawn from another. - [Plasmids, Mobile Elements and How Resistance Spreads](https://lightmysky.com/learn/science/plasmids-mobile-elements-and-how-resistance-spreads-mt_Vk0qOY64qv): Many resistance genes sit on plasmids and transposons that move between replicons and between cells, often several at once on one element. That is why resistance spreads faster than any single bacterial lineage could carry it. - [CRISPR: A Bacterial Defence Turned into a Tool](https://lightmysky.com/learn/science/crispr-a-bacterial-defence-turned-into-a-tool-mt_0joPWRvOLw): Bacteria keep fragments of past invaders in an array and use transcripts of those fragments to guide a nuclease to matching sequences. Supplying a guide of our own choosing turns the same system into a way of cutting a chosen site in any genome. - [Pathogenesis: Adhesion, Invasion and Virulence Factors](https://lightmysky.com/learn/science/pathogenesis-adhesion-invasion-and-virulence-factors-mt_8SPj_E5foc): Causing disease takes a sequence of steps: reaching a surface, sticking to it, getting past defences and obtaining nutrients such as iron. Each step depends on specific molecules, and losing one of them can make a pathogen harmless. - [Exotoxins, Endotoxin and How Damage Is Actually Done](https://lightmysky.com/learn/science/exotoxins-endotoxin-and-how-damage-is-actually-done-mt_RhMqBY_YhR): Some damage comes from secreted proteins with precise targets inside host cells, and some from a membrane component released when Gram-negative cells break up. The two differ in specificity, in potency and in whether heat destroys them. - [Antimicrobial Targets, Resistance Mechanisms and Selective Toxicity](https://lightmysky.com/learn/science/antimicrobial-targets-resistance-mechanisms-and-selective-toxicity-mt_fta5Ty8Liu): A useful drug hits something the microbe has and we do not, such as the wall, the ribosome or a folate enzyme. Resistance arises by changing the target, destroying the drug, pumping it out or keeping it from entering, and the drug does not create those changes but selects for them. - [Epidemiology: Incidence, the Reproduction Number and Tracking an Outbreak](https://lightmysky.com/learn/science/epidemiology-incidence-the-reproduction-number-and-tracking-an-outbreak-mt_f2tT08sEki): How fast a disease spreads is summarised by the average number of new cases one case produces, and that number falls as susceptible people run out or are protected. Incidence and prevalence answer different questions, and confusing them misreads an outbreak. - [Applied Microbiology: Fermentation, Bioremediation and Host Microbiomes](https://lightmysky.com/learn/science/applied-microbiology-fermentation-bioremediation-and-host-microbiomes-mt_WcfGvV_dD9): Microbial metabolism is put to work to make foods and medicines, to break down pollutants and to keep host surfaces occupied by harmless residents. In each case the practical question is which conditions favour the organism we want over the ones we do not. - [Synthetic Circuits: Switches, Oscillators and Why They Misbehave in Cells](https://lightmysky.com/learn/science/synthetic-circuits-switches-oscillators-and-why-they-misbehave-in-cells-mt_xRJGSHidqo): A toggle switch and a ring oscillator are built from the same motifs found in natural networks, then fail in ways the design did not predict. This stop treats retroactivity, competition for shared resources and mutation as engineering constraints. - [Metabolic Engineering: Redirecting Flux Through a Production Host](https://lightmysky.com/learn/science/metabolic-engineering-redirecting-flux-through-a-production-host-mt_fjz3EA-dDa): Making a host produce a chosen molecule means moving carbon and reducing power away from growth without killing the cell. This stop designs that trade using pathway balance, branch-point control and regulation that switches on at the right time. - [The Host Microbiome: Composition, Causation and Intervention](https://lightmysky.com/learn/science/the-host-microbiome-composition-causation-and-intervention-mt_-F8lNccQCU): Sequencing a community gives composition, and composition on its own cannot say what causes what. This stop moves from a survey to a causal claim using gnotobiotic transfer, controlled intervention and a stated mechanism.