Plasmid in the context of "DNA virus"

Virulence is a pathogen's or microorganism's ability to cause damage to a host.

In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to cause disease—is determined by its virulence factors. In the specific context of gene for gene systems, often in plants, virulence refers to a pathogen's ability to infect a resistant host. Virulence can also be transferred using a plasmid.

In molecular biology and genetics, transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). For transformation to take place, the recipient bacterium must be in a state of competence, which might occur in nature as a time-limited response to environmental conditions such as starvation and cell density, and may also be induced in a laboratory.

Transformation is one of three processes that lead to horizontal gene transfer, in which exogenous genetic material passes from one bacterium to another, the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium). In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium.

In molecular cloning, a vector is any particle (e.g., plasmids, cosmids, Lambda phages) used as a vehicle to artificially carry a foreign nucleic sequence – usually DNA – into another cell, where it can be replicated and/or expressed. A vector containing foreign DNA is termed recombinant DNA. The four major types of vectors are plasmids, viral vectors, cosmids, and artificial chromosomes. Of these, the most commonly used vectors are plasmids. Common to all engineered vectors are the origin of replication, a multicloning site, and a selectable marker.

The vector itself generally carries a DNA sequence that consists of an insert (in this case the transgene) and a larger sequence that serves as the "backbone" of the vector. The purpose of a vector which transfers genetic information to another cell is typically to isolate, multiply, or express the insert in the target cell. All vectors may be used for cloning and are therefore cloning vectors, but there are also vectors designed specially for cloning, while others may be designed specifically for other purposes, such as transcription and protein expression. Vectors designed specifically for the expression of the transgene in the target cell are called expression vectors, and generally have a promoter sequence that drives the expression of the transgene. Simpler vectors called transcription vectors are only capable of being transcribed but not translated: they can be replicated in a target cell but not expressed, unlike expression vectors. Transcription vectors are used to amplify their insert.

Bacillus cereus biovar anthracis is a variant of the Bacillus cereus bacterium that has acquired plasmids similar to those of Bacillus anthracis. As a result, it is capable of causing anthrax. In 2016, it was added to the CDC's list of select agents and toxins.

Bacillus cereus biovar anthracis infection has caused significant mortality in numerous mammalian species, including chimpanzees.

Extrachromosomal DNA (abbreviated ecDNA) is any DNA that is found off the chromosomes, either inside or outside the nucleus of a cell. Most DNA in an individual genome is found in chromosomes contained in the nucleus. Multiple forms of extrachromosomal DNA exist, and, while some of these serve important biological functions, they can also play a role in diseases such as cancer.

In prokaryotes, nonviral extrachromosomal DNA is primarily found in plasmids, whereas, in eukaryotes extrachromosomal DNA is primarily found in organelles. Mitochondrial DNA is a main source of this extrachromosomal DNA in eukaryotes. The fact that this organelle contains its own DNA supports the hypothesis that mitochondria originated as bacterial cells engulfed by ancestral eukaryotic cells. Extrachromosomal DNA is often used in research into replication because it is easy to identify and isolate.

A microbiome (from Ancient Greek μικρός (mikrós) 'small' and βίος (bíos) 'life') is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps et al. as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity". In 2020, an international panel of experts published the outcome of their discussions on the definition of the microbiome. They proposed a definition of the microbiome based on a revival of the "compact, clear, and comprehensive description of the term" as originally provided by Whipps et al., but supplemented with two explanatory paragraphs, the first pronouncing the dynamic character of the microbiome, and the second clearly separating the term microbiota from the term microbiome.

The microbiota consists of all living members forming the microbiome. Most microbiome researchers agree bacteria, archaea, fungi, algae, and small protists should be considered as members of the microbiome. The integration of phages, viruses, plasmids, and mobile genetic elements is more controversial. Whipps's "theatre of activity" includes the essential role secondary metabolites play in mediating complex interspecies interactions and ensuring survival in competitive environments. Quorum sensing induced by small molecules allows bacteria to control cooperative activities and adapts their phenotypes to the biotic environment, resulting, e.g., in cell–cell adhesion or biofilm formation.

Virulence factors (preferably known as pathogenicity factors or effectors in botany) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the following:

• colonization of a niche in the host (this includes movement towards and attachment to host cells)
• immunoevasion, evasion of the host's immune response
• immunosuppression, inhibition of the host's immune response (this includes leukocidin-mediated cell death)
• entry into and exit out of cells (if the pathogen is an intracellular one)
• obtain nutrition from the host

Specific pathogens possess a wide array of virulence factors. Some are chromosomally encoded and intrinsic to the bacteria (e.g. capsules and endotoxin), whereas others are obtained from mobile genetic elements like plasmids and bacteriophages (e.g. some exotoxins). Virulence factors encoded on mobile genetic elements spread through horizontal gene transfer, and can convert harmless bacteria into dangerous pathogens. Bacteria like Escherichia coli O157:H7 gain the majority of their virulence from mobile genetic elements. Gram-negative bacteria secrete a variety of virulence factors at host–pathogen interface, via membrane vesicle trafficking as bacterial outer membrane vesicles for invasion, nutrition and other cell-cell communications. It has been found that many pathogens have converged on similar virulence factors to battle against eukaryotic host defenses. These obtained bacterial virulence factors have two different routes used to help them survive and grow: