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Polyamines are required for normal growth in sinorhizobium meliloti

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JournalMicrobiology (Reading, England)
DateAccepted/In press - 19 Jan 2018
DateE-pub ahead of print - 12 Feb 2018
DatePublished (current) - 1 Apr 2018
Issue number4
Volume164
Number of pages14
Pages (from-to)600-613
Early online date12/02/18
Original languageEnglish

Abstract

Polyamines (PAs) are ubiquitous polycations derived from basic L-amino acids whose physiological roles are still being defined. Their biosynthesis and functions in nitrogen-fixing rhizobia such as Sinorhizobium meliloti have not been extensively investigated. Thin layer chromatographic and mass spectrometric analyses showed that S. meliloti Rm8530 produces the PAs, putrescine (Put), spermidine (Spd) and homospermidine (HSpd), in their free forms and norspermidine (NSpd) in a form bound to macromolecules. The S. meliloti genome encodes two putative ornithine decarboxylases (ODC) for Put synthesis. Activity assays with the purified enzymes showed that ODC2 (SMc02983) decarboxylates both ornithine and lysine. ODC1 (SMa0680) decarboxylates only ornithine. An odc1 mutant was similar to the wild-type in ODC activity, PA production and growth. In comparison to the wild-type, an odc2 mutant had 45% as much ODC activity and its growth rates were reduced by 42, 14 and 44% under non-stress, salt stress or acid stress conditions, respectively. The odc2 mutant produced only trace levels of Put, Spd and HSpd. Wild-type phenotypes were restored when the mutant was grown in cultures supplemented with 1mM Put or Spd or when the odc2 gene was introduced in trans. odc2 gene expression was increased under acid stress and reduced under salt stress and with exogenous Put or Spd. An odc1 odc2 double mutant had phenotypes similar to the odc2 mutant. These results indicate that ODC2 is the major enzyme for Put synthesis in S. meliloti and that PAs are required for normal growth in vitro.

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© 2018 The Authors.This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details

    Research areas

  • Homospermidine, Norspermidine, Ornithine decarboxylase, Polyamines, Putrescine, S. meliloti, Spermidine

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