Browsing tag: bakterie Gram-ujemne


Osmoadaptation and potassium transport systems in Gram-negative bacteria
W. Małek, S. Wdowiak-Wróbel , M. Targońska, M. Kalita, S. Gnat

1. Wstęp. 2. Systemy transportu K+ do komórki bakteryjnej. 2.1. System Trk. 2.2. System Ktr. 2.3. System Kdp. 2.4. System Kup. 3. Systemy wypływu K+ z komórki bakteryjnej. 4. Regulacja systemów transportu K+ do komórki bakteryjnej. 4.1. Kontrola systemów transportu K+ na poziomie ich aktywności. 4.2. Osmotyczna regulacja transportera Kdp na poziomie transkrypcji. 5. Podsumowanie

Abstract: Potassium (K+) is the major intracellular cation in bacterial cells. It plays a key role in maintaining the cell turgor, pH, adaptation to osmotic conditions, enzyme activation, and gene expression. The intracellular concentration of K+ is generally much higher than that in a growth medium and bacteria use a number of transporters and efflux pumps to maintain respective K+ concentration in cytoplasm. The best characterized K+ uptake systems in Gram-negative bacteria are: Trk, Kup, Ktr, and Kdp. Under hyperosmotic stress, in potassium-replete media at neutral and alkaline pH, the Trk system is the main K+ importer. It is a low – affinity, multiunit protein complex encoded by constitutively expressed genes that are. Under acidic conditions, when the activity of Trk is insufficient, a single component, i.e. the constitutive Kup transporter, with the affinity for K+ similar to that of the Trk system, is thought to be important. The Ktr transporter, resembling that of the Trk system, is composed of a membrane-spanning protein and a peripheral membrane-associated nucleotide – binding subunit. The Kdp-ATPase is a high affinity K+ uptake system that is expressed at very low potassium concentrations in the environment and in response to a decrease in cell turgor. Turgor, which is a signal and end the resulte of K+ import, is involved not only in the regulation of the Kdp transporter expression but also in the control of the activity of potassium uptake systems.

1. Introduction. 2. K+ uptake systems in bacterial cells. 2.1. Trk system. 2.2. Ktr system. 2.3. Kdp system. 2.4. Kup system. 3. K+ efflux systems in bacterial cells. 4. Regulation of K+ uptake systems. 4.1. Control of K+ uptake system activities. 4.2. Osmotic regulation of Kdp expression. 5. Summary

Bakteriocyny bakterii Gram-ujemnych – struktura, mechanizm działania i zastosowanie

Bacteriocins of Gram-negative bacteria – structure, mode of action and potential applications
U. Błaszczyk, J. Moczarny

1. Wprowadzenie. 2. Klasyfikacja bakteriocyn bakterii Gram-ujemnych. 3. Produkcja kolicyn przez bakterie kolicynogenne. 3.1. Synteza kolicyn. 3.2. Eksport kolicyn z komórek producenta. 4. Mechanizmy działania kolicyn. 4.1. Translokacja. 4.2. Efekt letalny kolicyn. 5. Charakterystyka i podział mikrocyn. 5.1. Struktura i genetyka wybranych mikrocyn. 5.1.1. MccE492. 5.1.2. MccJ25. 5.1.3. MccC7-C51. 5.2. Mechanizmy działania mikrocyn. 5.2.1. MccE492. 5.2.2. MccJ25. 5.2.3. MccC7-C51. 6. Potencjalne zastosowanie kolicyn i mikrocyn. 7. Podsumowanie

Abstract: Bacteriocins are a diverse group of ribosomally synthesized peptides or proteins secreted by bacteria, which help them to compete in their local environments for the limited nutritional resources. Bacteriocins kill or inhibit the growth of other bacteria. Generally, these molecules have a narrow spectrum of antibacterial activity, but some of them demonstrate a broad spectrum of action. Bacteriocins from Gram-negative bacteria are divided into two main groups: high molecular mass proteins (30–80 kDa) known as colicins, and low molecular mass peptides (between 1–10 kDa) termed microcins. Colicins are produced by Escherichia coli strains harbouring a colicinogenic plasmid. Such colicinogenic strains are widespread in nature and are especially abundant in the gut of animals. The biosynthesis of colicins is mediated by the SOS regulon, which becomes activated in the response to DNA damage. The colicin synthesis is lethal for the producing cells as a consequence of the concomitant biosynthesis of the colicin lysis protein. Microcins are usually highly stable molecules, which are resistant to proteases, extreme pH values and temperatures. They are produced by enteric bacteria under stress conditions, particularly nutrient depletion. Microcins are encoded by gene clusters carried by plasmids or in certain cases by the chromosome. In this review, we have summarized the most important information about structure and properties of bacteriocins from Gram-negative bacteria, their diverse mechanisms of action and potential application as food preservatives and in livestock industry.

1. Introduction. 2. Classification of bacteriocins from Gram-negative bacteria. 3. Production of colicins by colicinogenic bacteria. 3.1. Colicin synthesis. 3.2.  Export of colicins from bacteriocin-producing cells. 4. Modes of colicin action. 4.1. Translocation. 4.2. Lethal effect of colicins. 5. Characteristics and classification of microcins. 5.1. Structure and genetics of selected microcins. 5.1.1. MccE492. 5.1.2. MccJ25. 5.1.3. MccC7-C51. 5.2. Mechanisms of action of microcins. 5.2.1. MccE492. 5.2.2. MccJ25. 5.2.3. MccC7-C51. 6. Potential applications of colicins and microcins. 7. Summary