Bacterial plasma membranes are somewhat simpler than those of most eukaryotes. Along with phospholipids, eukaryotic cells include cholesterol and other large, flat, largely non-polar substances that help maintain and stiffen the membrane. Bacteria are cholesterol-free. Additionally, eukaryotes usually include a large number of complex lipoproteins (proteins with associated lipids) and glycoproteins (proteins with sugars attached). These derivatized proteins fulfill a number of the same functions as the cell wall and capsule in bacteria. Additionally, eukaryotes have a complex internal membrane system comprised of the Golgi apparatus, endoplasmic reticula, vesicles, mitochondria, and a nuclear membrane. None of these are present in Eubacteria. Certain bacteria contain tiny folds in their plasma membranes, which allow for the performance of certain specialized processes, such as the ATP-driven active transport of ions noted above, as well as photosynthesis in blue-green algae. There are no cytoplasmic membranes, though. Thus, the cytoplasm is a pretty homogenous solution devoid of structure. It does feature a variety of cytoplasmic inclusions that serve as storage for a variety of essential metabolites. These include phosphate metachromatic granules, glycogen (a glucose polymer), starch and salt grains, and poly(3-hydroxyalkanoate), the bacterial analogue of fat.
Despite the lack of a nucleus, the chromosome is often restricted to a tiny part of the cell called the nucleoid and is connected to the inner membrane. Bacterial genomes are much smaller than those of eukaryotes. E. coli, for example, contains 4.6 million base pairs of DNA, compared to three billion in humans. As is the case with eukaryotes, the DNA is tightly wound to fit within the cell. However, unlike in eukaryotes, the DNA is not bound to histone proteins. Much of our knowledge about DNA replication comes from studies of bacteria, notably E. coli, and the mechanics of this process are addressed elsewhere in this wiki. In contrast to eukaryotic replication, bacterial replication starts at a single point and progresses in both directions around the circle. Two circular chromosomes are formed as a consequence, which are split during cell division. Plasmids reproduce similarly.
While this results in an average of 1.3 bacteria per human cell, the quantities may vary greatly across individuals and can fluctuate dramatically with each defecation. They estimate that each human has between 30 and 50 trillion bacterial cells. Women may also have a larger ratio of bacterial cells to human cells due to a deficiency of human cells, particularly red blood cells. While this research excludes fungus, viruses, and archaea, all of which contribute to the human microbiome and so increase the ratio of microbes to human cells, the often quoted ratio of 10:1 for bacterial cells to human cells is most likely inaccurate. While I will no longer be able to use this amusing fact in my descriptions of the microbiome, this does not diminish the critical role of bacterial cells in human health.
Bacteria are exceptional in their capacity to destroy a wide array of chemical substances. Microorganisms classified into highly specialized groups play a critical role in the mineralization of particular kinds of organic molecules. The breakdown of cellulose, one of the most prevalent components of plant tissues, is mostly facilitated by aerobic bacteria of the genus Cytophaga. Bacteria that are capable of digesting petroleum hydrocarbons are often utilized to clean up oil spills. Following the 1989 Exxon Valdez oil disaster, several beaches in Prince William Sound were fertilized in an effort to promote the development of such bacteria. These attempts were successful on beaches that were not heavily oiled. Bacteria degrade organic stuff in sewage and agricultural wastes, preventing it from polluting the environment. Apart from organic matter, bacteria are capable of degrading metal cyanides from industrial sites, assisting in the cleanup of radioactive waste, recovering metal from low-grade ores, and degrading some insecticides.
