Presence of a gene encoding choline sulfatase in Sinorhizobium meliloti bet operon: choline-O-sulfate is metabolized into glycine betaine.
نویسندگان
چکیده
Glycine betaine is a potent osmoprotectant accumulated by Sinorhizobium meliloti to cope with osmotic stress. The biosynthesis of glycine betaine from choline is encoded by an operon of four genes, betICBA, as determined by sequence and mutant analysis. The betI and betC genes are separated by an intergenic region containing a 130-bp mosaic element that also is present between the betB and betA genes. In addition to the genes encoding a presumed regulatory protein (betI), the betaine aldehyde dehydrogenase (betB), and the choline dehydrogenase (betA) enzymes also found in Escherichia coli, a new gene (betC) was identified as encoding a choline sulfatase catalyzing the conversion of choline-O-sulfate and, at a lower rate, phosphorylcholine, into choline. Choline sulfatase activity was absent from betC but not from betB mutants and was shown to be induced indifferently by choline or choline-O-sulfate as were the other enzymes of the pathway. Unlike what has been shown in other bacteria and plants, choline-O-sulfate is not used as an osmoprotectant per se in S. meliloti, but is metabolized into glycine betaine. S. meliloti also can use this compound as the sole carbon, nitrogen, and sulfur source for growth and that depends on a functional bet locus. In conclusion, choline-O-sulfate and phosphorylcholine, which are found in higher plants and fungi, appear to be substrates for glycine betaine biosynthesis in S. meliloti.
منابع مشابه
Molecular characterization of the bet genes encoding glycine betaine synthesis in Sinorhizobium meliloti 102F34.
As a first step towards the elucidation of the molecular mechanisms responsible for the utilization of choline and glycine betaine (betaine) either as carbon and nitrogen sources or as osmoprotectants in Sinorhizobium meliloti, we selected a Tn5 mutant, LTS23-1020, which failed to grow on choline but grew on betaine. The mutant was deficient in choline dehydrogenase (CDH) activity, failed to ox...
متن کاملFunctional expression of Sinorhizobium meliloti BetS, a high-affinity betaine transporter, in Bradyrhizobium japonicum USDA110.
Among the Rhizobiaceae, Bradyrhizobium japonicum strain USDA110 appears to be extremely salt sensitive, and the presence of glycine betaine cannot restore its growth in medium with an increased osmolarity (E. Boncompagni, M. Osteras, M. C. Poggi, and D. Le Rudulier, Appl. Environ. Microbiol. 65:2072-2077, 1999). In order to improve the salt tolerance of B. japonicum, cells were transformed with...
متن کاملOccurrence of choline and glycine betaine uptake and metabolism in the family rhizobiaceae and their roles in osmoprotection
The role of glycine betaine and choline in osmoprotection of various Rhizobium, Sinorhizobium, Mesorhizobium, Agrobacterium, and Bradyrhizobium reference strains which display a large variation in salt tolerance was investigated. When externally provided, both compounds enhanced the growth of Rhizobium tropici, Sinorhizobium meliloti, Sinorhizobium fredii, Rhizobium galegae, Agrobacterium tumef...
متن کاملBetS is a major glycine betaine/proline betaine transporter required for early osmotic adjustment in Sinorhizobium meliloti.
Hybridization to a PCR product derived from conserved betaine choline carnitine transporter (BCCT) sequences led to the identification of a 3.4-kb Sinorhizobium meliloti DNA segment encoding a protein (BetS) that displays significant sequence identities to the choline transporter BetT of Escherichia coli (34%) and to the glycine betaine transporter OpuD of Bacillus subtilis (30%). Although the ...
متن کاملUptake of glycine betaine and its analogues by bacteroids of Rhizobium meliloti.
Bacteroids isolated from alfalfa nodules induced by Rhizobium meliloti 102F34 transported glycine betaine at a constant rate for up to 30 min. Addition of sodium salts greatly increased the uptake activity, whereas other salts or non-electrolytes had less effect. The apparent Km for glycine betaine uptake was 8.3 microM and V was about 0.84 nmol min-1 (mg protein)-1 in the presence of 200 mM-Na...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Proceedings of the National Academy of Sciences of the United States of America
دوره 95 19 شماره
صفحات -
تاریخ انتشار 1998