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Contact-dependent Growth Inhibition
Contact-dependent growth inhibition (CDI) is a phenomenon where a bacterial cell may deliver a polymorphic toxin molecule into neighbouring bacterial cells upon direct cell-cell contact, causing growth arrest or cell death. Discovery CDI is now a blanket term to describe interbacterial competition that relies on direct cell-cell contact in bacteria. However, the phenomenon was first discovered in 2005 in the isolate EC93 of ''Escherichia coli'' found in rat intestine, and, in this case, was mediated by a Type V secretion system. This isolate dominated the rat's gut flora and appeared to be particularly good at outcompeting lab strains of ''E. coli'' when grown in co-culture''.'' The novel part of this discovery was the fact that the inhibitory effects of the isolated ''E. coli'' appeared to require direct cell-cell contact. Before CDI was discovered in this isolate, the only systems known to mediate direct interbacterial competition by intoxication were toxins secreted into the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymorphic Toxins
Polymorphic toxins (PTs) are multi-domain proteins primarily involved in competition between bacteria but also involved in pathogenesis when injected in eukaryotic cells. They are found in all major bacterial clades. Bacteria live in complex multispecies communities such as biofilms and human-associated microbiotas. The dynamics and structure of these communities are greatly influenced by interbacterial competition through the secretion of toxic effectors. Bacteria have evolved several systems to outcompete their neighbors by poisoning them through a contact-dependent killing (including effectors of type V and VI secretion systems) or the release of soluble toxins (including colicins) in the environment. Definition Polymorphic toxins are bacterial exotoxins which share common features regarding their domain architecture. Each family of PTs is defined by a conserved N-terminal region associated with diverse C-terminal (CT) toxic domains, which can be found in several other PT fa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connections". Pearson Education. San Francisco: 2003. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: ''Bacteria'' (formerly Eubacteria) and ''Archaea'' (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, Eukaryota. In the study of the origins of life, prokaryotes are thought to have arisen before eukaryotes. Besides the absence of a nucleus, prokaryotes also lack mitochondria, or most of the other membrane-bound organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components within the cytop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guanosine Pentaphosphate
(p)ppGpp, guanosine pentaphosphate and tetraphosphate, also known as the "magic spot" nucleotides, are alarmones involved in the stringent response in bacteria that cause the inhibition of RNA synthesis when there is a shortage of amino acids. This inhibition by (p)ppGpp decreases translation in the cell, conserving amino acids present. Furthermore, ppGpp and pppGpp cause the up-regulation of many other genes involved in stress response such as the genes for amino acid uptake (from surrounding media) and biosynthesis. Discovery ppGpp and pppGpp were first identified by Michael Cashel in 1969. These nucleotides were found to accumulate rapidly in ''Escherichia coli'' cells starved for amino acids and inhibit synthesis of ribosomal and transfer RNAs. It is now known that (p)ppGpp is also produced in response to other stressors including carbon and phosphate starvation. Historically, literature surrounding (p)ppGpp have given conflicting findings and information on its role in bacte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clone (cell Biology)
A clone is a group of ''identical'' cells that share a ''common ancestry'', meaning they are derived from the same cell. Clonality implies the state of a cell or a substance being derived from one source or the other. Thus there are terms like ''polyclonal''—derived from many clones; ''oligoclonal''—derived from a few clones; and ''monoclonal''—derived from one clone. These terms are most commonly used in context of antibodies or immunocytes. Contexts This concept of clone assumes importance as all the cells that form a clone share common ancestry, which has a very significant consequence: shared genotype. # One of the most prominent usage is in describing a clone of B cells. The B cells in the body have two important phenotypes (functional forms)—the antibody secreting, terminally differentiated (that is, they cannot divide further) plasma cells, and the memory and the naive cells—both of which retain their proliferative potential. # Another important area where one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Persister Cells
Persister cells are subpopulations of cells that resist treatment, and become antimicrobial tolerant by changing to a state of dormancy or quiescence. Persister cells in their dormancy do not divide. The tolerance shown in persister cells differs from antimicrobial resistance in that the tolerance is not inherited and is reversible. When treatment has stopped the state of dormancy can be reversed and the cells can reactivate and multiply. Most persister cells are bacterial, and there are also fungal persister cells, yeast persister cells, and cancer persister cells that show tolerance for cancer drugs. History Recognition of bacterial persister cells dates back to 1944 when Joseph Bigger, an Irish physician working in England, was experimenting with the recently discovered penicillin. Bigger used penicillin to lyse a suspension of bacteria and then inoculate a culture medium with the penicillin-treated liquid. Colonies of bacteria were able to grow after antibiotic exposure. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with water (hydrolysis) using amylase enzymes as catalyst, which produces constituent sugars (monosaccharides, or oligosaccharides). They range in structure from linear to highly branched. Examples include storage polysaccharides such as starch, glycogen and galactogen and structural polysaccharides such as cellulose and chitin. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct properties from their monosaccharide building blocks. They may be amorphous or even insoluble in water. When all the monosaccharides in a polysaccharide are the same type, the polysaccharide is called a homopolysaccharide or homoglycan, but when more t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pilus
A pilus (Latin for 'hair'; plural: ''pili'') is a hair-like appendage found on the surface of many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some researchers reserve the term ''pilus'' for the appendage required for bacterial conjugation. All conjugative pili are primarily composed of pilin – fibrous proteins, which are oligomeric. Dozens of these structures can exist on the bacterial and archaeal surface. Some bacteria, viruses or bacteriophages attach to receptors on pili at the start of their reproductive cycle. Pili are antigenic. They are also fragile and constantly replaced, sometimes with pili of different composition, resulting in altered antigenicity. Specific host responses to old pili structures are not effective on the new structure. Recombination genes of pili code for variable (V) and constant (C) regions of the pili (similar to immunoglobulin diversity). As the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPSs). The cells within the biofilm produce the EPS components, which are typically a polymeric conglomeration of extracellular polysaccharides, proteins, lipids and DNA. Because they have three-dimensional structure and represent a community lifestyle for microorganisms, they have been metaphorically described as "cities for microbes". Biofilms may form on living or non-living surfaces and can be prevalent in natural, industrial, and hospital settings. They may constitute a microbiome or be a portion of it. The microbial cells growing in a biofilm are physiologically distinct from planktonic cells of the same organism, which, by contrast, are single cells that may float or swim in a liquid medium. Biofilms can form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bacillus Subtilis
''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus'', ''B. subtilis'' is rod-shaped, and can form a tough, protective endospore, allowing it to tolerate extreme environmental conditions. ''B. subtilis'' has historically been classified as an obligate aerobe, though evidence exists that it is a facultative anaerobe. ''B. subtilis'' is considered the best studied Gram-positive bacterium and a model organism to study bacterial chromosome replication and cell differentiation. It is one of the bacterial champions in secreted enzyme production and used on an industrial scale by biotechnology companies. Description ''Bacillus subtilis'' is a Gram-positive bacterium, rod-shaped and catalase-positive. It was originally named ''Vibrio subtilis'' by Christian Gottfried Ehrenberg, and renamed ''B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homologous Recombination
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may be also RNA in viruses). Homologous recombination is widely used by cells to accurately DNA repair harmful breaks that occur on both strands of DNA, known as double-strand breaks (DSB), in a process called homologous recombinational repair (HRR). Homologous recombination also produces new combinations of DNA sequences during meiosis, the process by which eukaryotes make gamete cells, like sperm and egg cells in animals. These new combinations of DNA represent genetic variation in offspring, which in turn enables populations to adapt during the course of evolution. Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses. Horizontal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
N-terminus
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amine group is bonded to the carboxylic group of another amino acid, making it a chain. That leaves a free carboxylic group at one end of the peptide, called the C-terminus, and a free amine group on the other end called the N-terminus. By convention, peptide sequences are written N-terminus to C-terminus, left to right (in LTR writing systems). This correlates the translation direction to the text direction, because when a protein is translated from messenger RNA, it is created from the N-terminus to the C-terminus, as amino acids are added to the carboxyl end of the protein. Chemistry Each amino acid has an amine group and a carboxylic group. Amino acids link to one another by peptide bonds which form through a dehydration reaction that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gram-positive Bacteria
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Conversely, gram-negative bacteria cannot retain the violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells, making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain (sa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
