There are five types of microbes. Bacteria are single-celled organisms that move around using their flagella, which are thin protrusions that look like a whip or tail. Protozoa feed on other microbes by engulfing the organisms or absorbing them through their cells. Viruses consist of genetic material coated in a shell. These microbes take over their host cells so they can reproduce. The fungi group includes molds, mushrooms and yeast. These organisms range in size from one single cell to very large chains of cells. Algae live in the water or in very moist land environments. These organisms produce their own food using energy from the sun.
Bacteria come in three major shapes: rod, spiral and round. Some bacterial organisms join together to make chains or clusters. Scientists use protein typing, staining and other laboratory procedures to identify specific types of bacteria. Protozoa consist of a single cell with a nucleus, an organelle surrounded by membranes. These microbes do not have cell walls. Some protozoa reproduce asexually, which means they do not require a partner to reproduce. Instead, the organism splits in two, separates into a number of cells or forms buds that break off of the parent cell. In protozoa that reproduce sexually, two cells fuse together during fertilization.
Scientists identify viruses by looking for specific characteristics. These microbes do not contain their own cell organelles or cytoplasm. They rely on their host cells to create and assemble new viral components instead of reproducing on their own. Most viruses contain DNA or RNA, but they rarely contain both of these nucleic acids. Scientists classify algae according to the pigments that give them color. Rhodophyta, known as red algae, contain phycobilin pigments, have no flagella and have a cell wall that consists of calcium carbonate. Brown algae, members of the division Phaeophyta, have carotenoid and xanthophyll pigments. These microbes have flagella and their cell walls consist of alignic acid, cellulose and sulfated polysaccharides. Chlorophyta, or green algae, also contain carotenoid and xanthophyll pigments. Some of these microbes have flagella, but others do not. Their cell walls consist of polysaccharides and cellulose.
Each of the five microbes benefits plants or animals in some way. Beneficial bacteria help the body function as it should. Lactobacillus acidophilus, for example, aids in normal digestion. Protozoa cause diseases in humans, but they help some insects break down cellulose in their digestive tracts. Fungi provide a food source for humans in the form of mushrooms. Penicillin, derived from Penicillum fungi, fights some bacterial infections. Viruses also cause diseases in humans, but researchers use viral organisms to develop vaccines and research the effects of viruses on the human body, resulting in better treatments for viral infections. Algae give off oxygen consumed by plants and animals. Algae also produce energy, which makes them a contender in the race to reduce greenhouse gases and produce cleaner energy.
Harmful bacteria, also known as pathogenic bacteria, cause infections in humans. Examples of these diseases include food poisoning, cholera, tetanus and bacterial pneumonia. Protozoa can enter the water supply and cause diseases such as babesiosis, amoebic dysentery, toxoplasmosis, giardial enteritis and coccidiosis. Humans sometimes develop fungal infections when they come into contact with fungi. Fungi cause ringworm, athlete's foot and yeast infections. Because viruses use host cells to replicate, they take over healthy cells and can cause serious illnesses. Examples of viral infections include HIV, viral meningitis, influenza, human papillomavirus, rabies and rotavirus. Algae also cause some diseases in humans. These conditions include amnesiac shellfish poisoning, protothecosis, ciguatera and paralytic shellfish poisoning.