Escherichia coli in the context of "Gut flora"

A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in Jain literature authored in 6th-century BC India. The scientific study of microorganisms began with their observation under the microscope in the 1670s by Anton van Leeuwenhoek. In the 1850s, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis, cholera, diphtheria, and anthrax.

Microorganisms are extremely diverse, representing most unicellular organisms in all three domains of life: two of the three domains, Archaea and Bacteria, only contain microorganisms. The third domain, Eukaryota, includes all multicellular organisms as well as many unicellular protists and protozoans that are microbes. Some protists are related to animals and some to green plants. Many multicellular organisms are also microscopic, namely micro-animals, some fungi, and some algae.

Regulation of gene expression, or gene regulation, includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA). Sophisticated programs of gene expression are widely observed in biology, for example to trigger developmental pathways, respond to environmental stimuli, or adapt to new food sources. Virtually any step of gene expression can be modulated, from transcriptional initiation, to RNA processing, and to the post-translational modification of a protein. Often, one gene regulator controls another, and so on, in a gene regulatory network.

Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed. Although as early as 1951, Barbara McClintock showed interaction between two genetic loci, Activator (Ac) and Dissociator (Ds), in the color formation of maize seeds, the first discovery of a gene regulation system is widely considered to be the identification in 1961 of the lac operon, discovered by François Jacob and Jacques Monod, in which some enzymes involved in lactose metabolism are expressed by E. coli only in the presence of lactose and absence of glucose.

Filamentation is the anomalous growth of certain bacteria, such as Escherichia coli, in which cells continue to elongate but do not divide (no septa formation). The cells that result from elongation without division have multiple chromosomal copies.

In the absence of antibiotics or other stressors, filamentation occurs at a low frequency in bacterial populations (4–8% short filaments and 0–5% long filaments in 1- to 8-hour cultures). The increased cell length can protect bacteria from protozoan predation and neutrophil phagocytosis by making ingestion of cells more difficult. Filamentation is also thought to protect bacteria from antibiotics, and is associated with other aspects of bacterial virulence such as biofilm formation.

A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.

Some examples of facultatively anaerobic bacteria are Staphylococcus spp., Escherichia coli, Salmonella, Listeria spp., Shewanella oneidensis and Yersinia pestis. Certain eukaryotes are also facultative anaerobes, including pupfish, fungi such as Saccharomyces cerevisiae and many aquatic invertebrates such as nereid polychaetes.

Kashechewan First Nation, locally known as Kash, is a Cree First Nation located on the northern shore of the Albany River in Northern Ontario, Canada, within territory covered by Treaty 9. The community is located on the west coast of James Bay. Kashechewan came into being when most of the Anglican families of Fort Albany on the south shore of the river moved north in 1958–1961. Kashechewan was granted its own band council under the Indian Act in 1977, though the two still share a reserve, Fort Albany 67. The population was estimated to be about 2,000 as of 2024, according to the CBC, and as of October 2024, the total population of Kashechewan and Fort Albany, which are reported together by CIRNAC, was 5,597.

The First Nation was the subject of international media attention due to the discovery of E. coli in the community's water in October 2005, which brought popular consciousness to the health, housing, and economic crises facing the community.