Gram-negative bacteria in the context of "Citrobacter"

Yersinia pestis (Y. pestis; formerly Pasteurella pestis) is a gram-negative, non-motile, coccobacillus bacterium without spores. It is related to pathogens Yersinia enterocolitica, and Yersinia pseudotuberculosis, from which it evolved. Yersinia pestis is responsible for the disease plague, which caused the Plague of Justinian and the Black Death, one of the deadliest pandemics in recorded history. Plague takes three main forms: pneumonic, septicemic, and bubonic. Y. pestis is a facultative anaerobic parasitic bacterium that can infect humans primarily via its host the Oriental rat flea (Xenopsylla cheopis), but also through aerosols and airborne droplets for its pneumonic form. As a parasite of its host, the rat flea, which is also a parasite of rats, Y. pestis is a hyperparasite.

Y. pestis was discovered in 1894 by Alexandre Yersin, a Swiss/French physician and bacteriologist from the Pasteur Institute, during an epidemic of the plague in Hong Kong. Yersin was a member of the Pasteur school of thought. Kitasato Shibasaburō, a Japanese bacteriologist who practised Koch's methodology, was also engaged at the time in finding the causative agent of the plague. However, Yersin actually linked plague with a bacillus, initially named Pasteurella pestis; it was renamed Yersinia pestis in 1944.

Cyanobacteria (/saɪˌænoʊbækˈtɪəriə/ sy-AN-oh-bak-TEER-ee-ə) are a group of autotrophic gram-negative bacteria of the phylum Cyanobacteriota that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" (from Ancient Greek κύανος (kúanos) 'blue') refers to their bluish green (cyan) color, which forms the basis of cyanobacteria's informal common name, blue-green algae.

Cyanobacteria are probably the most numerous taxon to have ever existed on Earth and the first organisms known to have produced oxygen, having appeared in the middle Archean eon and apparently originated in a freshwater or terrestrial environment. Their photopigments can absorb the red- and blue-spectrum frequencies of sunlight (thus reflecting a greenish color) to split water molecules into hydrogen ions and oxygen. The hydrogen ions are used to react with carbon dioxide to produce complex organic compounds such as carbohydrates (a process known as carbon fixation), and the oxygen is released as a byproduct. By continuously producing and releasing oxygen over billions of years, cyanobacteria are thought to have converted the early Earth's anoxic, weakly reducing prebiotic atmosphere, into an oxidizing one with free gaseous oxygen (which previously would have been immediately removed by various surface reductants), resulting in the Great Oxidation Event and the "rusting of the Earth" during the early Proterozoic, dramatically changing the composition of life forms on Earth. The subsequent adaptation of early single-celled organisms to survive in oxygenous environments likely led to endosymbiosis between anaerobes and aerobes, and hence the evolution of eukaryotes during the Paleoproterozoic.

Escherichia coli (/ˌɛʃəˈrɪkiə ˈkoʊlaɪ/ ESH-ə-RIK-ee-ə KOH-lye) is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are part of the normal microbiota of the gut, where they constitute about 0.1%, along with other facultative anaerobes. These bacteria are mostly harmless or even beneficial to humans. For example, some strains of E. coli benefit their hosts by producing vitamin K₂ or by preventing the colonization of the intestine by harmful pathogenic bacteria. These mutually beneficial relationships between E. coli and humans are a type of mutualistic biological relationship—where both the humans and the E. coli are benefitting each other. E. coli is expelled into the environment within fecal matter. The bacterium grows massively in fresh fecal matter under aerobic conditions for three days, but its numbers decline slowly afterwards.

Some serotypes, such as EPEC and ETEC, are pathogenic, causing serious food poisoning in their hosts. Fecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease. This transmission method is occasionally responsible for food contamination incidents that prompt product recalls. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination. A growing body of research, though, has examined environmentally persistent E. coli which can survive for many days and grow outside a host.

Pseudomonadota (synonym "Proteobacteria") is a major phylum of gram-negative bacteria. They include pathogenic and free-living (non-parasitic) genera. The phylum comprises six classes Acidithiobacillia, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Hydrogenophilia, and Zetaproteobacteria. The Pseudomonadota are widely diverse, with differences in morphology, metabolic processes, relevance to humans, and ecological influence.

Vibrio cholerae is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimp, and other shellfish. Some strains of V. cholerae are pathogenic to humans and cause a deadly disease called cholera, which can be derived from the consumption of undercooked or raw marine life species or drinking contaminated water.

V. cholerae was first described by Félix-Archimède Pouchet in 1849 as some kind of protozoa. Filippo Pacini correctly identified it as a bacterium and from him, the scientific name is adopted. The bacterium as the cause of cholera was discovered by Robert Koch in 1884. Sambhu Nath De isolated the cholera toxin and demonstrated the toxin as the cause of cholera in 1959.

Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria (Chromatiales, in part) and purple non-sulfur bacteria. Purple bacteria are anoxygenic phototrophs widely spread in nature, but especially in aquatic environments, where there are anoxic conditions that favor the synthesis of their pigments.

Enterobacteriaceae is a large family of Gram-negative bacteria. It includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but one classification places it in the order Enterobacterales of the class Gammaproteobacteria in the phylum Pseudomonadota. In 2016, the description and members of this family were emended based on comparative genomic analyses by Adeolu et al.

Enterobacteriaceae includes, along with many harmless symbionts, many of the more familiar pathogens, such as Salmonella, Escherichia coli, Klebsiella, and Shigella. Other disease-causing bacteria in this family include Enterobacter and Citrobacter. Members of the Enterobacteriaceae can be trivially referred to as enterobacteria or "enteric bacteria", as several members live in the intestines of animals. In fact, the etymology of the family is enterobacterium with the suffix to designate a family (aceae)—not after the genus Enterobacter (which would be "Enterobacteraceae")—and the type genus is Escherichia.

Plant pathology or phytopathology is the scientific study of plant diseases caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Plant pathology involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.