types of bacteria, and some will multiply inside the cytoplasm of other cells. These are different from pathogenic bacteria, which are dangerous to eukaryotic host organisms. Mutualists will grow on, in, or near other organisms for the mutual survival of the two organisms. For example, certain anaerobes require methanogenic Archaea (and vice versa) to survive. The Archaea species consumes hydrogen as part of their metabolic processes, while anaerobes require a low hydrogen environment in order to survive. Humans have numerous symbiotic or mutualistic bacteria that make vitamins and contribute to essential functions in the gut.
CLASSIFYING BACTERIA There is a wide diversity of bacteria, which can be classified on the basis of their metabolism, their cell structure, or on differences in certain cellular components. Modern ways of classifying bacteria involve looking at the genetics of the different species and is, in fact, how many different organisms are now classified. Historically, the term “bacteria” was applied to any single-celled prokaryote. Now, using genetics, there have been two domains identified: Bacteria and Archaea—two separate domains that have evolved from a common primordial ancestor. As it turns out, Archaea are closer to eukaryotes than they are to bacteria genetically. This has led to a three-domain system among cellular organisms, which are Bacteria, Archaea, and Eukarya. The Gram stain will characterize different bacteria into four main groups. This is just based on the characteristics of the cell wall. There are Gram-positive cocci, Grampositive bacilli, Gram-negative cocci and Gram-negative bacilli. Some organisms are not classified at all by this Gram-staining process and are considered “acid-fast” by virtue of other types of stains. Still other organisms are characterized by their ability to grow in certain media or through serological techniques. There are also the classifications of aerobic bacteria versus anaerobic bacteria. Using the standard in today’s modern medicine, which is to use the polymerase chain reaction in order to identify bacterial species and to classify them according to their genome, bacteria are now classified genomically rather than on the basis of their morphology, staining abilities, or metabolism. This has led to the identification of
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