This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: stachydrine catabolism
|Superclasses:||Degradation/Utilization/Assimilation → Amines and Polyamines Degradation|
Some taxa known to possess this pathway include : Sinorhizobium meliloti Rm2011
Expected Taxonomic Range: Proteobacteria
Betaines are quarternary amine derivatives of amino acids that can serve as osmoprotectants. Stachydrine, known as N, N-dimethyl proline or proline betaine, can be used by Sinorhizobium meliloti Rm2011 as a carbon and nitrogen source and as an osmoprotectant [Goldmann91]. In the absence of osmotic stress, Sinorhizobium meliloti Rm2011 can degrade stachydrine, whereas stachydrine degradation in osmotically stressed cells is strongly reduced, resulting in accumulation of the osmoprotectant [Gloux89].
Stachydrine is proposed to undergo two sequential demethylations, the first demethylation produces N-methyl proline and the subsequent demethylation produces proline, which then enters general metabolism [Goldmann94, Burnet00, Phillips98a]. The degradation of stachydrine is similar to glycine betaine degradation, which also involves two sequential demethylations and produces monomethyl glycine [Smith88a]. The initial demethylation of stachydrine is proposed to be catalyzed by a Rieske type iron-sulfur monooxygenase system, similar to those involved in aromatic hydrocarbon degradation [Burnet00]. The second demethylation step is proposed to be catalyzed by an enzyme showing homology to oxidoreductase flavoproteins [Phillips98a].
The stc2, 3, and 4 genes, which appear to encode for the monooxygenase system that catalyzes the initial demethylation of stachydrine, are intermingled with the nodulation and nitrogen fixation function on the symbiotic plasmid, pSym [Goldmann94]. The stc2, 3, and 4 genes appear to have a functional role in nodulation, as Stc- mutants exhibited delayed and reduced nodulations [Goldmann94]. However, the stc genes do not appear to be regulated by the nod gene regulatory system, since the stc genes are inducible when nodD functions are inactivated and they are transcribed in the opposite direction of the nod genes [Goldmann94].
The stcD gene, which appears to encode for the oxidorectuase flavoprotein that catalyzes the second demethylation, is not located on the pSym plasmid [Phillips98a], unlike the stc2, 3, and 4 genes.
Burnet00: Burnet MW, Goldmann A, Message B, Drong R, El Amrani A, Loreau O, Slightom J, Tepfer D (2000). "The stachydrine catabolism region in Sinorhizobium meliloti encodes a multi-enzyme complex similar to the xenobiotic degrading systems in other bacteria." Gene 2000;244(1-2);151-61. PMID: 10689197
Goldmann91: Goldmann, A., Boivin, C., Fleury, V., Message, B., Lecoeur, L., Maille, M., Tepfer, D. "Betaine Use by Rhizosphere Bacteria: Genes Essentional for Trigonelline, Stachydrine, and Carnitine Catabolism in Rhizobium meliloti are Located on pSym in the Symbiotic Region." Mol. Plant Microbe Interact. (1991) 4: 571-578.
Goldmann94: Goldmann A, Lecoeur L, Message B, Delarue M, Schoonejans E, Tepfer D "Symbiotic plasmid genes essential to the catabolism of proline betaine, or stachydrine, are also required for efficient nodulation by Rhizobium meliloti." FEMS Microbiology Letters 115: 305-312 (1994).
Phillips98a: Phillips DA, Sande ES, Vriezen JAC, de Bruijn FJ , Le Rudulier D , Joseph CM (1998). "A new genetic locus in sinorhizobium meliloti is involved in stachydrine utilization." Appl Environ Microbiol 64(10);3954-60. PMID: 9758825
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