by number of bacteria, plants, and ..
Synthesis of glycine betaine from exogenous choline in the moderately halophilic bacterium …
Cocamidopropyl betaine - Wikipedia
In this thesis, the glycine betaine synthesis in two extremely halophilic bacteria Actinopolyspora halophila and Ectothiorhodospira halochloris is investigated.A.
In the extreme halophytic phototrophic bacterium , glycinebetaine is not synthesized from choline, but rather by direct -methylation of the amino acid, glycine (Galinksi and Truper, 1994; Nyyssola et al, 2000; 2001):(where SAM = -adenosylmethionine, and SAHC = -adenosylhomocysteine).
Regulatory Factors Associated with Synthesis of the Osmolyte ..
Microorganisms must be able to adapt to changes in the osmolarity of their environment. To adapt to these changes, bacteria accumulate some compounds, named compatible solutes, that confer protection against the deleterious effect of the low water activity (). Moderately halophilic bacteria are defined as those which can grow optimally between 0.5 and 2.5 M salt (). Among this heterogeneous group of microorganisms, Halomonas elongata has a very promising potential for use in biotechnology (), and since it can grow at a very wide range of salinities (from 0.5 to 3 M NaCl in a minimal medium) (), it is also a good model organism to study the molecular basis of prokaryotic osmoadaptation (). To cope with changes in the salt concentration of the environment, H. elongata is able to synthesize ectoine and hydroxyectoine (, ) and to take up a variety of organic compounds which can serve as osmoprotectants when present externally (). Accordingly, exogenous glycine betaine (called betaine hereafter), choline, and choline-O-sulfate have been demonstrated to play an osmoprotective role in H. elongata (). Many organisms, including gram-positive (, ) and gram-negative () bacteria, as well as higher plants (, ), can generate betaine for osmoprotection by oxidation of choline. We have investigated the transport of choline and its conversion to the osmoprotectant compound betaine in the moderately halophilic bacterium H. elongata. The role of salinity and betaine in the regulation of this osmoprotective mechanism has also been investigated.
Synthesis of the osmoprotectant glycine betaine from the exogenously provided precursor choline or glycine betaine aldehyde confers considerable osmotic stress tolerance to Bacillus subtilis in high-osmolarity media. Using an Escherichia coli mutant (betBA) defective in the glycine betaine synthesis enzymes, we cloned by functional complementation the genes that are required for the synthesis of the osmoprotectant glycine betaine in B. subtilis. The DNA sequence of a 4.1-kb segment from the cloned chromosomal B. subtilis DNA was established, and two genes (gbsA and gbsB) whose products were essential for glycine betaine biosynthesis and osmoprotection were identified. The gbsA and gbsB genes are transcribed in the same direction, are separated by a short intergenic region, and are likely to form an operon. The deduced gbsA gene product exhibits strong sequence identity with members of a superfamily of specialized and nonspecialized aldehyde dehydrogenases. This superfamily comprises glycine betaine aldehyde dehydrogenases from bacteria and plants with known involvement in the cellular adaptation to high-osmolarity stress and drought. The deduced gbsB gene product shows significant similarity to the family of type III alcohol dehydrogenases. B. subtilis mutants with defects in the chromosomal gbsAB genes were constructed by marker replacement, and the growth properties of these mutant strains in high-osmolarity medium were analyzed. Deletion of the gbsAB genes destroyed the choline-glycine betaine synthesis pathway and abolished the ability of B. subtilis to deal effectively with high-osmolarity stress in choline- or glycine betaine aldehyde-containing medium. Uptake of radiolabelled choline was unaltered in the gbsAB mutant strain. The continued intracellular accumulation of choline or glycine betaine aldehyde in a strain lacking the glycine betaine-biosynthetic enzymes strongly interfered with the growth of B. subtilis, even in medium of moderate osmolarity. A single transcription initiation site for gbsAB was detected by high-resolution primer extension analysis. gbsAB transcription was initiated from a promoter with close homology to sigma A-dependent promoters and was stimulated by the presence of choline in the growth medium.
stress in enteric bacteria has ..
Glycine betaine is a solute which is able to restore and maintain the osmotic balance of living cells. In this thesis, the glycine betaine synthesis in two extremely halophilic bacteria Actinopolyspora halophila and Ectothiorhodospira halochloris is investigated.
The data presented in this work indicate that the de novo synthesis of glycine betaine proceeds via the threefold methylation of glycine. S-adenosylmethionine acts as the methyl group donor in the reactions. The genes encoding this pathway were cloned and successfully expressed in Escherichia coli. In E. halochloris, glycine sarcosine N-methyltransferase (GSMT) and sarcosine dimethylglycine N-methyltransferase (SDMT) catalyze the reaction sequence. In A. halophila all three methylation reactions appear to be catalyzed by a fusion protein. The methyltransferases from the two bacteria show high sequence homology.
Synthesis of Glycine Betaine from Exogenous Choline in the ..
MetaCyc glycine betaine biosynthesis IV (from glycine)
Department of Horticulture and Landscape Architecture
Betaine in human nutrition
Department of Horticulture and Landscape Architecture : ..
Cellular absorption of betaine has been described in many organisms from bacteria to ..
Pathway of proline synthesis in bacteria
Several osmolytes have been identified in methanogens, including α-glutamate, dimethylglycine, betaine, β-glutamate, β-glutamine, 1,3,4,6-tetracarboxyhexane, N-acetyl-β-lysine, and di-myo-inositol-1,1-phosphate (, , , , , , ). Among these, betaine is a widely adopted osmolyte which has a crucial osmoprotective function in plants, animals, and eubacteria (, , ). A study by Pollard and Wyn Jones () demonstrated that intracellularly accumulated betaine up to 500 mM had no inhibitory effect on the cell. Moreover, their work also showed the ability of betaine to prevent the inhibition by NaCl of malate dehydrogenase activity in Horleum vulgare (). Uptake or transport of betaine and its precursors as compatible solutes under osmotic stress are common phenomena among many organisms (, , , , , , , , ). However, only three microorganisms have demonstrated the capability for de novo synthesis of betaine: the halophilic methanogen Methanohalophilus portucalensis FDF1, the extremely haloalkalophilic sulfur bacterium Ectothiorhodospira halochloris, and the salt-tolerant cyanobacterium Aphanothece halophytica (–, , , , ).
Glycine Betaine Biosynthesized from Glycine Provides …
De novo synthesis of betaine in M. portucalensis FDF1 was originally confirmed by growing the cells in a defined medium that contained methanol and 15NH4Cl instead of 14NH4Cl. The 1H-decoupled 15N NMR spectrum of the extract from these cells indicated incorporation of the label into betaine (). The intracellular level of betaine increased with an increase in the external salt concentration, implying that it functions as an osmolyte (). The turnover rate of betaine measured by 13CH3OH pulse-12CH3OH chase experiments was low (0.022 h−1), which is consistent with its role as an osmolyte (). Although unable to synthesize betaine de novo, most eubacteria can accumulate it by taking up choline and converting it to betaine (, ). The steps involved in the uptake of choline and its enzymatic conversion into betaine in Escherichia coli and other organisms have also been extensively studied (, , , , , ). Previous studies have demonstrated that M. portucalensis possesses a high-affinity and highly specific betaine transport system (); however, it does not internalize choline (data not shown). This feature suggests that betaine accumulation through a choline uptake and oxidation process is unlikely to occur in this halophilic methanogen.
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