Mineral salts are simple, inorganic substances made up of metallic chemical elements, such as iron, sodium, potassium, calcium and magnesium, or of non-metallic elements, such as chlorine and phosphorus.
They can be found in their non-solubilized form as a part of structures in an organism, like the calcium in bones. They can also be found solubilized in water as ions: such as, the sodium and potassium cations within cells.
The most important inorganic substances for living organisms are water, mineral salts, carbon dioxide and molecular oxygen. (There are several other inorganic substances without which cells would die.)
Inorganic substances, such as water, mineral salts, molecular oxygen and carbon dioxide, are small molecules made up of few atoms. Organic substances, in general, such as glucose, fatty acids and proteins, are much more complex molecules made of sequences of carbons bound in carbon chains. The capacity of carbon to form chains is one of the main chemical facts that allowed for the emergence of life on the planet.
The chemical elements that make up the majority of the molecules of living organisms are oxygen (O), carbon (C), hydrogen (H) and nitrogen (N).
Pathogenic bacteria have characteristics known as virulence factors, which help them to parasite their hosts. Some bacteria have fimbriae, cilium-like structures that hook the bacterial cell onto the host tissue. Some bacteria are specialized in intracellular parasitism. Others secrete toxins, molecules that cause disease. In some cases, bacterial population growth causes food poisoning by toxins. Generally, bacterial disease is caused by bacterial population growth resulting in the invasion and destruction of tissues or by bacterial toxins that contaminate an organism.
Bacteria are used by industry in various ways. Some vaccines are made of attenuated pathogenic bacteria or antigens present in bacteria. One of the most ancient uses of bacteria is the fermentation of milk to produce yogurt, cheese and curds (even before people knew of the existence of bacteria, these microorganisms were already used to make those products). Some methods of antibiotic production involve bacteria. Recombinant DNA technology (genetic engineering) allows the industrial production and commercialization of human proteins, such as insulin for diabetics, which is synthesized by mutant bacteria. Some bacteria can produce fuel, like methane gas.
Some human diseases caused by bacteria are tuberculosis, pertussis, diphtheria, bacterial meningitis, gonorrhea, syphilis, the bubonic plague, leptospirosis, cholera, typhoid fever, Hansen’s disease, trachoma, tetanus and anthrax.
Bacteria are responsible for the decomposition process at the end of food chains and food webs. In this process, they also release useful gases and nutrients for other living organism. Bacteria that live within the digestive tracts of ruminants and some insects digest cellulose for these animals. Some bacteria also participate in the nitrogen cycle, carrying out the fixation of nitrogen, nitrification and denitrification, almost always in a mutualistic ecological interaction with plants. Bacteria present within living organisms, such as those that live inside the bowels, compete with other pathogenic bacteria, therefore helping to control the population of noxious agents. There are also bacteria that cause diseases and bacteria used in the production of medical drugs.
The excessive Growth or mass destruction of bacteria can impact entire ecosystems. For example, when a river is polluted by organic material, the population of aerobic bacteria increases since the organic material is food for them. This large number of bacteria then exhausts the oxygen dissolved in the water and other aerobic organisms (like fish) experience mass death.
These are three types of archaebacteria. Halophilic archaebacteria only survive in salt-rich environments (even the salinity of the sea is not enough for them). Thermoacidophilic archaebacteria are characterized by living in high temperatures and low pHs. Methanogen archaebacteria are those that release methane gas (CH₄). They are found in swamps.
Prokaryotic organisms are classified into two main groups: archaebacteria and bacteria (the latter is also known as eubacteria).
Compared to bacteria, archaebacteria present basic differences, such as the chemical composition of their plasma membrane and cell wall and different enzymes related to DNA and RNA metabolism.